Veterinary Parasitology- The Practical Veterinarian

Copyright 2001 by ButterworthHeinemann

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Library of Congress Cataloging-in-Publication DataBallweber, Lora Rickard, 1958

Veterinary parasitology / Lora Rickard Ballweber.p. ; cm. (Practical veterinarian)

Includes bibliographical references and index.ISBN 0-7506-7261-7 (alk. paper)

1. Veterinary parasitology. I. Title. II. Series.[DNLM: 1. Parasitic Diseases, AnimalHandbooks. SF 810.A3 B193v 2001]SF810.A3 B35 2001]636.089696dc21 00-063083

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Series Preface

The Practical Veterinarian series was developed to helpveterinary students, veterinarians, and veterinary techni-cians find answers to common questions quickly. Unlikelarger textbooks, which are filled with detailed informa-tion and meant to serve as reference books, all the booksin The Practical Veterinarian series are designed to cut tothe heart of the subject matter. Not meant to replace thereference texts, the guides in our series complement thelarger books by serving as an introduction to each topicfor those learning the subject matter for the first time oras a quick review for those who already have masteredthe basics of each subject.

The titles for the books in our series are selected toprovide information for the most common subjects onewould encounter in veterinary school and veterinarypractice. The authors are experienced and establishedclinicians who can present the subject matter in an easy-to-understand format. This helps both the first-time stu-dent of the subject and the seasoned practitioner toassess information often difficult to comprehend.

It is our hope that the books in The Practical Veteri-narian series will meet the needs of readers and serve asa constant source of practical and important informa-tion. We welcome comments and suggestions that will

vii

help us improve future editions of the books in thisseries.

Shawn P. Messonnier, D.V.M.

viii Series Preface

Preface

Unknowingly, I was first exposed to the discipline of vet-erinary parasitology as a youngster when my grandfa-ther, Roy V. Stambaugh, gave me his copy of a 1923USDA publication on the diseases of horses. In thumb-ing through it, I came upon an illustration of bots thatwere living in the stomach of the horse. While repulsed,I was at the same time fascinated that such a lifestyle wasoccurring with apparently little harm to the horse! Per-haps that is why, years later, I chose to accept an assist-antship to study for a Masters in parasitology ratherthan ruminant nutrition, and I have thoroughly enjoyedveterinary parasitology over essentially the past 20 years.As first a student and now a veterinary medical educator,I have seen numerous reference materials on this sub-ject. Many texts have become standards in the requiredbook list, but the most common complaint from veteri-nary students is they are not user-friendly and are tooverbose. Therefore, I was delighted to have the oppor-tunity to write a text that I hope is user-friendly. The out-line format was chosen because it is designed to presentinformation in a succinct, easy-to-read, and readilyaccessible format, thus, making this a quick referenceguide to the nuts and bolts of the parasites of veterinaryimportance designed for the veterinary medical student.

ix

When designing this book, I was confronted withthe same question we are all confronted with in ourcourses: what material to include. The first decision waswhether to limit it to the usual dogs, cats, horses, etc., orto include birds, reptiles, rodents, and other small mam-mals. Shear volume of material made the choice formeit would have to be limited to traditional domesti-cated animals (including poultry) with a few rodentsand small mammals included in the arthropod section.Next was which actual parasites to include. Decisionshere were governed by whether the parasite is common,has dire consequences if missed, or possesses someunique attribute or ability. Some parasites are encoun-tered so infrequently that inclusion in a quick referenceguide is not feasible. Others, such as Spirocerca lupi, areincluded because of a unique attribute; in this case, itsassociation with neoplasia. Still others, such as Acan-thocheilonema (=Dipetalonema) reconditum, are includedbecause of the difficulty in differentiating diagnosticstages from those of other, more pathogenic parasites;in this case, distinguishing microfilariae from those pro-duced by the heartworm, Dirofilaria immitis. Althoughsome parasites near and dear to me were not included,I believe that those essential to a veterinary medical education are.

The book begins with an introduction explainingsome basic concepts of parasitology and taxonomic clas-sification. Chapter 2 is devoted solely to ectoparasites.Chapter 3 is an introductory chapter to the endopara-

x Preface

sites, describing the characteristics and generalized lifecycles of each group (protozoans, nematodes, cestodes,digenetic trematodes, acanthocephalans). Host-parasitelists are provided here as well. The subsequent chaptersdescribe the parasites according to body organ system.Chapters 4 to 6 describe the parasites of the gastroin-testinal tract, Chapter 7 describes the cardiopulmonarysystem, and Chapter 8 covers the remaining organ sys-tems. Geographic distribution and relative significanceto both veterinary medicine and public health areincluded for each parasite as a guide to the student as tothe general importance of the parasite.

Information related to treatment of helminths hasbeen summarized in tables for approved compoundsavailable in the United States. Dosages and treatmentschedules should be verified on package inserts prior touse. In cases where approved drugs are not available,information on types and dosages of drugs used suc-cessfully is included within the text. However, thereader is reminded that this constitutes extra-label druguse and it is the responsibility of the attending veteri-narian to determine the dosage and best treatment forthe animal. Always be aware of contraindications; forexample, many collies and dogs of related herdingbreeds may suffer potentially fatal idiosyncratic reac-tions to ivermectin at doses as low as 100 mg/kg.

I would like to acknowledge Dr. Robert Bergstromwho offered me that assistantship in veterinary para-sitology those many years ago and fostered my fascina-

Preface xi

tion with this subject. I would also like to thank Dr. EricHoberg and past and present colleagues at MississippiState University, including Drs. Carla Siefker, AlanRathwell, Harry Jacobson, George Hurst, CarolynBoyle, Sharon Black, Terry Engelken, and Linda Pote,for their help and stimulating discussions over the pastfew years. Finally, I express sincere appreciation to myhusband for his patience and understanding when Ineeded to be working rather than fishing, and to therest of my family who do not know exactly what it is Ido, but have always supported my decision to do it.

L.R.B.

xii Preface

1Introduction

Symbiosis refers to any association, either temporary orpermanent, that exists between two organisms of differ-ent species. There are several types of symbiotic relation-ships, including predator-prey, phoresis, mutualism,commensalism, and parasitism. In the predator-prey rela-tionship, the association is one that is very short andresults in harm (i.e., death) to one member while bene-fiting the other. Phoresis refers to a relationship in whichone member of the association is mechanically carriedabout by the second member with no harm inflicted oneither. Mutualism refers to a relationship in which bothmembers of the association benefit as a result of the rela-tionship. Commensalism refers to a relationship in whichone member of the association benefits while the second

1

member receives neither benefit nor harm. Finally, para-sitism refers to a relationship in which one member ofthe associationthe parasitelives in or on the sec-ondthe host. The parasite derives nutritional benefitfrom the host and is usually considered harmful to thehost, although the degree of harm can vary greatly. It isthe parasites and parasitic diseases of domestic animalsthat we refer to as the discipline of veterinary parasitol-ogy, the subject of this book.

To understand parasites and the diseases they cause,one must first understand what a species is and the con-cepts of classification. Although not perfect, the mostwidely accepted definition of a species is an interbreedingpopulation that is reproductively isolated from other suchpopulations. For example, horses are host to manyspecies of small strongyles. As many as 1520 species ofthese parasites may be found living in the colon of thesame horse at the same time, yet they cannot interbreedand are, thus, separate species. We recognize the fact thatmany of these species are related, some more closely thanothers, by considering them to be in the same genus or inclosely related genera within the same family. These rela-tionships, then, are the basis of the Linnaean system ofclassification. There are millions of organisms on earth,each of which may have a different common name in dif-ferent regions of the world. Conversely, the same com-mon name may be used in different regions of the worldto refer to different species. In order to bring about sta-bility and universality, a system of classification has been

2 Introduction

devised in which all organisms are given a Latin binomial.This consists of a genus name (capitalized) followed bythe species name (lowercase). Both genus and speciesnames are italicized. Each species refers to a specificorganism and both genus and species names are givenwhen referring to that particular organism, for example,Dirofilaria immitis for the heartworm of dogs. Similarspecies are grouped within the same genus, similar gen-era within the same family, similar families within thesame order, similar orders within the same class, similarclasses within the same phylum, and similar phylagrouped together in the same kingdom. In order tocommunicate with colleagues, it is important to at leastlearn the species names of the parasites.

Identification is the process of determining to whichof these taxonomic groups an organism belongs. It is,generally, based on morphologic characteristics that areused to describe a certain species, genus, family, etc.Diagnosis, on the other hand, usually refers to the processof determining the cause of a disease. In this book, theterm diagnosis is used to refer to the process of deter-mining the presence of or how to identify a particularparasite species and not the determination of the causeof the clinical signs present. For example, diarrhea in ayoung calf may have a bacterial or viral cause and havelittle or nothing to do with the coccidial infection pres-ent. However, identification of oocysts in the feces maylead the uninitiated to misdiagnose coccidiosis. Alwaysrememberinfection does not equal disease.

Introduction 3

2Arthropods

Ectoparasites, most of which are arthropods, are thoseparasites that live on the body of the host. Some spendtheir entire life on the host, others spend only parts oftheir life on the host, while still others only occasionallyvisit the host. The ectoparasites most veterinarians dealwith directly are those that live all or much of their lifeon the host. Those that are periodic visitors to the hostare not usually on the animals when presented to thepractitioner. Although called upon to treat the effects ofthese periodic parasites, most veterinarians are notdirectly involved in their control. Consequently, thischapter focuses on those parasites spending all or muchof their life on the host with only brief mention of theperiodic parasites.

5

Classification of the ArthropodsKingdom: AnimaliaPhylum: ArthropodaClass: Arachnida (scorpions, spiders, mites, and

ticks)Order: Acarina (mites and ticks)Class: Insecta (insects)Order: Mallophaga (chewing or biting lice)

Anoplura (sucking lice)Siphonaptera (fleas)Diptera (two-winged flies)

Importance Intermediate hosts for various parasites.

Vectors for bacteria, viruses, and other pathogens.

Direct causal agents of disease.

Produce venoms that may be toxic.

Morphology Arachnids: body divided into two parts (cephalotho-

rax [fusion of head and thorax] and abdomen) orcompletely fused; adults with four pairs of legs;antennae absent; wingless.

6 Arthropods

Insects: body divided into three parts (head, thorax,abdomen); adults with three pairs of legs; antennaepresent; wings present or absent.

Ticks (Arachnida)Ticks are divided into two families: the Argasidae (softticks) and the Ixodidae (hard ticks). Table 21 outlinesthe important characteristics of each family.

Life Cycle

Simple metamorphosis with larval and nymphalstages resembling adults.

Separate sexes with females laying eggs off the host.

Larva (six legs, no reproductive organs) hatches,feeds on host and molts to nymph.

Nymph (eight legs, no functional reproductiveorgans) feeds on host and molts to another nymph(soft ticks) or adult (hard ticks).

Soft ticks have two or more nymphal stages; hardticks have only one.

All adult hard ticks feed on blood whereas not alladult soft ticks do.

Soft ticks tend to live inside (burrows, dens, hutches,etc.), feed rapidly, and spend relatively little time onthe host. Hard ticks tend to live outdoors, feedslowly, and spend longer time on the host.

Arthropods 7

8 Arthropods

Tab

le 2

1Im

port

ant C

hara

cter

istic

s of

Sof

t and

Har

d Ti

cks

Char

acte

rA

rgas

idae

(So

ft T

icks

)Ix

odid

ae (

Har

d T

icks

)

Scut

um

Abse

ntPr

esen

t

mal

es

cove

rs e

ntire

dor

sal

surfa

ce

fe

mal

es

cove

rs p

art o

f dor

sal

surfa

ce

Mou

thpa

rtsH

idde

n w

hen

view

ed fr

om th

e do

rsal

sur

face

Visi

ble

whe

n vi

ewed

from

the

dors

al s

urfa

ce

Feed

ing

Larv

ae fe

ed s

low

ly, o

ver s

ever

al

days

; nym

phs

and

adul

ts fe

ed

quic

kly,

sev

eral

tim

es

Larv

ae, n

ymph

s, a

nd a

dults

feed

on

ce, r

equi

ring

seve

ral d

ays

to

repl

etio

n Li

fe s

tage

sEg

g, la

rva,

two

or m

ore

nym

phs,

ad

ult

Egg,

larv

a, n

ymph

, adu

lt

Most ticks cannot tolerate direct sunlight, dryness,or excessive rainfall; tick activity decreases duringthe cold months and increases during spring, sum-mer, and fall.

Hard ticks can be classified as either one-host (allstages on one host), two-host (two stages on one host),or three-host (all stages on different hosts) ticks.

Common Soft Ticks in North America

ARGAS SPP. In the United States, distributed along the Gulf of

Mexico and the Mexican border.

Parasitize wild and domestic birds, occasionallyhumans.

Active primarily in evening hours.

Annoyance leads to decreased egg production;heavy infestations may cause anemia.

Development from egg to adult may take as little as30 days; may survive months (larvae, nymphs) ormore than 2 years (adults) without a blood meal.

OTOBIUS MEGNINI (SPINOSE EAR TICK) Generally distributed throughout North America.

Parasitize cattle, horses, other domestic animals, andhumans.

Arthropods 9

One-host tick in which larvae and nymphs feed inthe ear canal; unfed nymphs can survive as long as 2months.

Adults have vestigial mouthparts and do not feed;therefore, adult females lay a single clutch of eggs.

Common Hard Ticks in North America

RHIPICEPHALUS SANGUINEUS (BROWN DOG TICK) Three-host tick with all stages preferring dogs; can

feed on humans.

Originally found in the tropics; cannot overwinter incold, temperate regions but will survive indoors inthese areas; found in most of the United States andparts of southeast Canada.

Egg to egg development may be completed in as lit-tle as 2 months; unfed adults may survive for over ayear.

Transmit Babesia canis, Erlichia canis, possibly Hepato-zoon americanum.

AMBLYOMMA SPP. Two species are commonAmblyomma americanum

(lone star tick) and Amblyomma maculatum (Gulfcoast tick).

Both are three-host ticksadults prefer feeding onlarger animals (cattle and other livestock) and

10 Arthropods

other stages prefer feeding on foxes and similar-sized animals.

In the United States, A. maculatum is distributedalong Atlantic and Gulf coastal areas, whereas A.americanum is distributed in the southeastern region,into the Midwest and on the Atlantic coast.

Ambylomma americanum can produce severe anemiaand may transmit tularemia, Rocky Mountain spot-ted fever, and Lyme disease.

Amblyomma maculatum produces painful bite woundsthat swell and may become secondarily infected;implicated as a cause of tick paralysis; transmit Hepa-tozoon americanum.

DERMACENTOR SPP. Dermacentor variabilis (American dog tick)disjunct

populations occur across the United States, intoCanada, and Mexico.

Dermacentor andersoni (Rocky Mountain wood tick)widely distributed across western United States andCanada.

Both are three-host tickslarvae and nymphs preferfeeding on small rodents, adults prefer larger ani-mals (including dogs and humans).

Both can transmit Rocky Mountain spotted fever,tularemia, and can cause tick paralysis.

Arthropods 11

IXODES SPP. Several species or subspecies found across the

United States.

Three-host tick with larvae and nymphs preferringsmall rodents and adults preferring deer.

Transmits Lyme disease.

Other Important Genera

BOOPHILUS SPP. Two species of importance in North America

Boophilus microplus and Boophilus annulatus (Ameri-can cattle tick).

One-host ticks with B. annulatus preferring cattleand B. microplus preferring large animals in general(cattle, goats, deer, etc.).

Has been eradicated from the United States and,therefore, if encountered must be reported to stateand federal authorities.

Boophilus annulatus transmits Texas cattle fever (Babesiabigemina); both can transmit Anaplasma marginale.

HAEMAPHYSALIS SPP. Important parasite of wild mammals and birds;

rarely of dogs, cats, or humans.

Three-host ticks distributed from Alaska toArgentina.

12 Arthropods

Diagnosis

Ticks should be collected carefully in order to keep themouthparts intact. Preserving intact specimens in 70%ethanol or isopropyl alcohol is recommended, although5% formalin will do. The specific identification of tickscan be challenging, particularly if dealing with larval ornymphal forms. However, adults can be identified togenus using the shape of their capitulum and length oftheir mouthparts, the presence or absence of markings onthe scutum, and body structures. Table 22 presents keymorphologic characteristics that can be used to distin-guish the North American genera of hard ticks.

Treatment and Control

For dogs, dichlorvos, carbaryl, fipronil, and selamectincan be used. Fipronil on cats is highly effective. Flea andtick collars are available for dogs and cats. To control R.sanguineus indoors, spray building with Diazinon.Remove vegetation and debris from bed and yards todecrease tick survival. Spray or dust with acaricide to killthose that remain.

For lactating dairy cattle, coumaphos and dichlorvoscan be used. These and malathion may be used in non-lactating beef and dairy cattle. Coumaphos is effectivefor horses. Environmental modification for livestock isoften impractical.

Insecticidal dusts or emulsion concentrates are usedin the treatment of O. megnini infestations.

Arthropods 13

14 ArthropodsTa

ble

22

Key

Mor

phol

ogic

Cha

ract

eris

tics

Use

d to

Dis

tingu

ish

the

Nor

th A

mer

ican

G

ener

a of

Har

d Ti

cks

and

Boo

philu

s

Gen

us

An

al G

roov

e*

* Loc

atio

n of

gro

ove,

if p

rese

nt, i

n re

latio

n to

anu

s.

Bas

is C

apit

uli

or

Mou

thp

arts

Eyes

Scu

tal

Mar

kin

gsFe

stoo

ns

Ixod

esAn

terio

rM

outh

parts

long

Abse

ntIn

orna

te

Inor

nate

= n

o w

hite

mar

ks o

n th

e sc

utum

; orn

ate

= w

hite

mar

ks p

rese

nt o

n sc

utum

.

Abse

nt

Rhip

icep

halu

sPo

ster

ior

Hex

agon

al b

asis

ca

pitu

liPr

esen

tIn

orna

tePr

esen

t

Ambl

yom

ma

Post

erio

rM

outh

parts

muc

h lo

nger

than

ba

sis

capi

tuli

Pres

ent

Orn

ate

Pres

ent

Der

mac

ento

rAb

sent

Rect

angu

lar b

asis

ca

pitu

liPr

esen

tO

rnat

ePr

esen

t

Hae

ma-

phys

alis

Post

erio

rSe

cond

pal

pal s

eg-

men

t ar

ed la

t-er

ally

Abse

ntIn

orna

tePr

esen

t

Boo

philu

sAb

sent

Hex

agon

al b

asis

ca

pitu

li, s

hort

mou

thpa

rts

Pres

ent

Inor

nate

Abse

nt

Mites (Arachnida)Mites can be divided into two major groups: sarcopti-form and nonsarcoptiform mites. The sarcoptiformmites can be subdivided into those that burrow or tunnelwithin the epidermis and those that do not. Sarcopti-form mites are distinguished from nonsarcoptiformmites by possessing a round to oval-shaped body. Thelegs of sarcoptiform mites also have pedicels (stalks) atthe tips that may be long or short. If long, they may bejointed or unjointed. Suckers may be present at the tip ofthe stalk. These characteristics are very important foridentification. Although geographic distribution varieswith species of mite, in general, mites are found through-out the world.

Life Cycle

Simple metamorphosis with larval and nymphalstages resembling adults.

Separate sexes with females laying eggs on the host.

Larva (six legs) hatches, may or may not feed, andmolts to nymph.

Nymph (eight legs) feeds on host and molts toanother nymph (sarcoptiform mites living on sur-face) or adult (burrowing sarcoptiform mites; non-sarcoptiform mites).

Except for some mites of birds, mites tend to spendentire life on the host; for most mites, transmission

Arthropods 15

is primarily by direct contact although fomites canplay a role.

Sarcoptiform Mites

TUNNELING SARCOPTIFORM MITES Table 23 presentsthe host spectrum and characteristic lesions of the com-mon tunneling sarcoptiform mites.

SURFACE-DWELLING SARCOPTIFORM MITES Table 24presents the host spectrum and characteristic lesions of thecommon surface-dwelling sarcoptiform mites.

Non-Sarcoptiform Mites

DEMODEX SPP. These host-specific mites live in the hairfollicles and sebaceous glands of humans and mostdomestic animals. In most animals, these mites are con-sidered normal, nonpathogenic fauna of the skin. How-ever, particularly in the dog, serious disease can result.Transmission is by direct contact. The cigar-shaped bodymakes these mites easily recognizable.

Demodex canis Localized demodecosis: patchy alopecia, especially

of the muzzle, face, and bony projections on extrem-ities; nonpruritic; most recover spontaneously;recurrence is rare.

16 Arthropods

Arthropods 17

Tab

le 2

3H

ost,

Spec

ies,

Key

Cha

ract

eris

tics,

and

Les

ions

Cau

sed

by T

unne

ling

Sarc

optif

orm

Mite

s

Mit

eH

ost

Lesi

ons

Com

mon

Sit

esO

ther

Sarc

opte

s sc

abei

v.

cani

s

Dog

sIn

itial

ly

eryt

hem

a-to

us, t

hen

papu

lar;

beco

min

g cr

usty

, thi

ck-

ened

with

al

opec

ia,

prur

itis

Ears

, lat

eral

el

bow

s,

vent

ral

abdo

men

Zoon

otic

Sarc

opte

s sc

abei

v. s

uis

Pigs

Ina

mm

atio

n,

eryt

hem

a,

alop

ecia

, w

ith in

tens

e pr

uriti

s

Hea

d (e

ars,

no

se, e

yes)

in

itial

ly;

spre

ads

to

neck

, sho

ul-

ders

, bac

k

Zoon

otic

(con

tinue

s)

18 Arthropods

Tab

le 2

3(C

ontin

ued)

Mit

eH

ost

Lesi

ons

Com

mon

Sit

esO

ther

Not

oedr

es c

ati

Cat

s Ra

bbits

Yello

w c

rust

s,

thic

kene

d sk

in,

alop

ecia

Star

ts o

n ea

rs;

spre

ads

to

face

, nec

k,

paw

s, a

nd

hind

quar

-te

rs

Mos

t com

mon

ca

use

of fe

line

scab

ies

Trix

acar

us

cavi

aeG

uine

a pi

gsD

ry, s

caly

ski

n w

ith a

lope

-ci

a, d

erm

ati-

tis, e

xtre

me

prur

itis

Back

, nec

k,

shou

lder

sIn

fest

atio

ns c

an

lead

to

anor

exia

an

d de

ath

Cne

mid

ocop

tes

mut

ans

Poul

try

Wild

bird

sH

yper

kera

tosi

s w

ith le

gs

beco

min

g th

icke

ned,

de

form

ed

Legs

Com

mon

na

me:

sca

ly

leg

Arthropods 19

Cne

mid

ocop

tes

pila

e C

. jam

aice

nsis

Para

keet

s C

anar

ies

Leg

lesi

ons

as

for C

. m

utan

s;

crus

ty m

ass

on b

eak

Shan

ks a

nd

pads

of f

eet,

cere

, ven

t ar

ea, b

ack

Com

mon

na

me

for

faci

al le

sion

s =

sca

ly fa

ce

Cne

mid

ocop

tes

galli

nae

Poul

try

Pige

ons

Ina

mm

atio

n,

prur

itis;

fe

athe

rs

brea

k ea

sily

Back

, top

of

win

g, b

reas

t, th

ighs

, ven

t ar

ea

Bird

s m

ay

activ

ely

pull

out f

eath

ers

20 Arthropods

Tab

le 2

4H

ost,

Spec

ies,

Key

Cha

ract

eris

tics,

and

Les

ions

Cau

sed

by S

urfa

ce-

Dw

ellin

g Sa

rcop

tifor

m M

ites

Mit

eH

ost

Lesi

ons

Com

mon

Sit

esO

ther

Psor

opte

scu

nicu

liRa

bbits

Drie

d cr

ust i

n pi

nna;

bro

wn

disc

harg

e; o

ti-tis

med

ia m

ay

resu

lt

Ears

Can

als

o be

fo

und

on

hors

es, g

oats

, sh

eep

Psor

opte

s bo

vis

Cat

tlePr

uriti

c ar

eas

con-

sist

ing

of p

ap-

ules

, cru

sts,

th

icke

ned

skin

With

ers,

bac

k,

rum

pRe

porta

ble

and

quar

antin

able

Psor

opte

s ov

isSh

eep

Extre

mel

y pr

uriti

c;

cons

tant

rub-

bing

lead

s to

se

lf-m

utila

-tio

n; w

ool f

alls

ou

t; sk

in

Woo

led

area

s of

th

e bo

dyH

as b

een

erad

i-ca

ted

from

th

e U

nite

d St

ates

Arthropods 21

beco

mes

th

icke

ned,

cr

acks

, ble

eds

easi

ly; s

heep

be

com

e de

bil-

itate

d an

d ca

n di

eC

horio

ptes

sp

p.Ru

min

ants

H

orse

sSk

in b

ecom

es

thic

kene

d,

crus

ty; n

ot

over

ly p

rurit

ic

Skin

of l

ower

hi

nd le

gs, t

ail-

head

, esc

utch

-eo

n

Repo

rtabl

e in

so

me

stat

es

Oto

dect

es

cyan

otis

Dog

s C

ats

Ferre

ts

Inte

nsel

y pr

uriti

c;

muc

h da

rk

ceru

men

pro

-du

ced;

hea

d sh

akin

g ca

n ca

use

hem

atom

a of

th

e au

ral

pinn

a

Exte

rnal

ear

, ear

ca

nal;

has

been

foun

d ar

ound

the

base

of t

he

tail

If un

treat

ed, p

er-

fora

tion

of

the

tym

pani

c m

embr

ane

can

occu

r

Generalized demodecosis: occurs as a result of animmunodeficiency; diffuse alopecia, erythema, andsecondary bacterial infections; pruritic; rancid odor;difficult to ameliorate; poor prognosis.

Other Species These species are usually nonpatho-genic; however, lesions have been associated withinfestations. As for the dog, concomitant diseases areusually present with severe infestations.

Demodex cati and D. gatoi (cat) can cause alopecia, ery-thema, scaly or crusty dermatitis on face, neck, and ears.

Demodex bovis (cattle) and D. caprae (goats) can causepinhead and larger-sized pustules; found on theshoulders, trunk, and lateral aspect of the neck.

Demodex ovis (sheep) can cause localized, scalylesions; rare.

Demodex phylloides (pigs) can cause pustules aroundthe eyes and on the snout; can spread to ventral sur-face of the body.

Demodex caballi and D. equi (horses) may producepruritis, alopecia with scaling, or pustules; starts onthe neck or withers, spreading to head, forelimbs,and back.

Demodex aurati and D. criceti (hamsters, gerbils) cancause alopecia with scaling or scabs; found on therump and back (hamster) or face (gerbil).

22 Arthropods

PNEUMONYSSOIDES (=PNEUMONYSSUS) CANINUM Oval, pale yellow; 1.01.5 mm in length; all legs are

on the anterior half of the body.

Lives in nasal and paranasal sinuses of dogs; preva-lence in the United States is unknown.

Generally thought to be nonpathogenic; has beenassociated with sneezing, sinusitis, labored breath-ing, and disorders of the central nervous system (aresult of the sinusitis).

CHEYLETIELLA SPP. Species include Cheyletiella blakei (cats), C. parasitivo-

rax (rabbits), and C. yasguri (dogs).

Up to 386 266 m in size; have large hook-likeaccessory palpi on anterior end.

Mites are very motile; resemble moving flakes ofdandruff (common name: walking dandruff).

Causes a dry, scaly dermatitis; mild alopecia; perhapsskin thickening.

May infest humans causing a mild dermatitis.

DERMANYSSUS GALLINAE (RED MITE OF POULTRY) ANDORNITHONYSSUS SYLVIARUM (NORTHERN FOWL MITE)

Morphologically similar; approximately 1 mm inlength.

Parasitize chickens, wild birds; occasionally humans.

Arthropods 23

Ornithonyssus sylviarum usually found on birds, butalso can be found in nests and poultry houses; D. gal-linae usually found off birds.

Feeding activities cause irritation, weight loss, decreasedegg production, and anemia; may lead to death.

Diagnosis

The experienced clinician often can make an accurate diag-nosis based on the typical distribution and manner of thespread of lesions. However, a positive diagnosis depends onrecovery and identification of the mites. Skin scrapings,deep enough to draw blood, are the most common diag-nostic tool. Some mites are extremely difficult to find; there-fore, negative skin scrapings are inconclusive and animalsshould be examined repeatedly. Scrapings should be at themargins of active lesions. Additionally, for Demodex spp.,areas of normal skin should be scraped to determine if theinfection is generalized. For Cnemidocoptes spp., remove andexamine the underside of a loose scale. A strong hand lensmay be used to view Cheyletiella on the animal.

Table 25 presents a key to differentiate the commonsarcoptiform mites. Characteristic morphologic features ofnonsarcoptiform mites have already been presented.


Dogs and cats: oral or SQ ivermectin at 0.20.4 mg per kgor topical ivermectin at 0.5 mg per kg is effective against sar-

24 Arthropods

coptic mange in dogs. Clip hair and remove crusty materialwith keratolytic shampoo first. Ivermectin at 0.3 mg per kgand doramectin at approximately 0.3 mg per kg has beeneffective against notoedric mange in cats. Otodectic acaria-sis in dogs and cats requires a thorough cleaning of the earcanal followed by acaricidal otic solutions. Selamectin isapproved for use against this parasite. Oral (three treat-ments at weekly intervals) or SC (two treatments at 2 weeksapart) ivermectin at 0.20.4 g per kg is effective in dogs.Ivermectin at 0.20.5 g per kg administered orally, SC, ortopically is effective in cats. Treatment intervals for oral andSC in cats is as for dogs; use a minimum of two treatmentsgiven 2 weeks apart for pour-on. For demodectic mange indogs, the localized form has been treated with 1% rotenone

Arthropods 25

Table 25 Key to the Genera of Common Sarcoptiform Mites

1a. Short, unjointed pedicels. . . . . . . . . . . . . . . . . . . . . . . . . 2 1b. Long pedicels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2a. Pedicels on rst, second, and fourth pairs of legs of

females and all legs of males; body of males with large, posterior lobes . . . . . . . . . . . . . . . . . . . . . . . . . .Chorioptes

2b. Pedicels on rst and second pairs of legs of females and all legs of males; body of male with small, posterior lobes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Otodectes

3a. Long, jointed pedicels . . . . . . . . . . . . . . . . . . . . Psorpotes 3b. Long, unjointed pedicels . . . . . . . . . . . . . . . . . . . . . . . . . 4 4a. Anus at posterior margin of body . . . . . . . . . . . Sarcoptes 4b. Anus on dorsal surface of body . . . . . . . . . . . . Notoedres

ointment or 5% benzoyl peroxide once or twice daily. Donot use Amitraz for treatment of the localized form. How-ever, Amitraz is approved and recommended for use againstthe generalized form. Continue treatment until no livemites are found on two successive skin scrapes. Daily oralivermectin at 0.6 mg per kg until resolution of infection (4months) and daily oral milbemycin oxime at 0.523.8 mgper kg for varying periods has also been used with mixedsuccess. For P. caninum, milbemycin oxime at 0.51.0 mgper kg orally once a week for 3 weeks was effective. ForCheyletiella, acaricidal shampoos approved for use on dogsor cats are effective as is fipronil in dogs. Ivermectin at0.20.4 mg per kg every 7 (orally) or 14 (SQ) days for 68weeks or pour-on ivermectin at 0.5 mg per kg given 2 weeksapart has also been used. Be sure to treat premises withresidual acaricidal spray.

Ruminants: acaricides effective against lice are alsogood for chorioptic mange in cattle. Eprinomectin isapproved for use in lactating dairy cattle. Sarcopticmange is reportable in cattle; should it occur, treatmentand control requirements will be outlined at that time.Psoroptic mange is also reportable and treatment andcontrol requirements will be outlined at that time.

Horses: lindane applied two times at weekly intervalshas been effective. Thoroughly clean stall and associatedequipment (e.g., feed buckets, curry combs).

Pigs: ivermectin at 0.3 mg per kg SQ is used againstsarcoptic mange.

Birds: efforts against D. gallinae are directed towards theenvironment. Periodic removal of litter and nest materials,

26 Arthropods

thorough cleaning, and high-pressure application ofresidual acaricides are recommended. For control of O.sylviarum, spray birds with appropriate ectoparasiticidesuch as malathion, carbaryl, or permethrin. As with allmedications, read and follow label directions. Cnemido-coptic mites may be treated with ivermectin at 0.2 mg perkg, administered parenterally or orally.

Guinea pigs: T. caviae can be treated with two dosesof ivermectin at 0.20.5 mg per kg SQ or orally, given 1week apart.

Rabbits: P. cuniculi can be treated with two injectionsof ivermectin at 0.20.4 mg per kg given 2 weeks apart.

Lice (Insecta)Lice are distributed across two orders, the Anoplura (suck-ing lice) and the Mallophaga (biting or chewing lice). Table26 outlines the important characteristics of each family.Although geographic distribution varies according to eachspecies of louse, in general, lice are distributed worldwide.

Life Cycle

Simple metamorphosis with nymphal stages resem-bling adults.

Spend entire life on the host; transmission primarilyby direct contact, but fomites can also play a role.

Separate sexes with adult females laying small(0.51.0 mm), whitish, oval eggs (nits); attachedfirmly to hair or feathers.

Arthropods 27

28 Arthropods

Tab

le 2

6Im

port

ant C

hara

cter

istic

s D

istin

guis

hing

the

Two

Ord

ers

of L

ice

Char

acte

rA

nop

lura

(Su

ckin

g Li

ce)

Mal

lop

hag

a (C

hew

ing

Lice

)

Col

orTe

nd to

be

gray

or r

ed d

epen

ding

on

how

muc

h bl

ood

has

been

in

gest

ed

Tend

to b

e ye

llow

Mou

thpa

rtsPi

erci

ng m

outh

parts

Che

win

g m

outh

parts

H

ead

Som

ewha

t poi

nted

, nar

row

er th

an

thor

axRo

unde

d he

ad, b

road

er th

an

thor

ax

Life

sta

ges

Egg,

thre

e ny

mph

s, a

dult

Egg,

thre

e ny

mph

s, a

dult

Atta

chm

ent

Tend

s to

rem

ain

atta

ched

to a

nim

alTe

nds

to b

e m

obile

, eas

y to

re

mov

e

Nymphs hatch from eggs; three nymphal stagesoccur prior to reaching the adult stage.

After mating, the adult female will lay eggs and thelife cycle begins again.

The time from egg to egg can take as little as 34 weeks.

Eggs generally do not hatch and neither nymphs noradults will live much longer than 1 week if removedfrom the host.

Common Lice

Lice are relatively host specific with most species ofanimals having some type of louse (common speciesand hosts are presented in Table 27); human lice(Phthirus pubis, Pediculus humanus) can occasionallybe found on dogs.

Sucking lice do not parasitize cats or birds.

Importance

Most lice problems manifest under crowded condi-tions, often in winter.

The presence of either type of louse can cause irri-tation, pruritis, scratching, licking, and restlessnessleading to loss of condition, poor weight gain,decreased milk production, etc.

Sucking lice can cause anemia.

Bite wounds can become secondarily infected.

Arthropods 29

30 ArthropodsTa

ble

27

Com

mon

Spe

cies

of C

hew

ing

(Ord

er: M

allo

phag

a) a

nd S

ucki

ng

(Ord

er: A

nopl

ura)

Lic

e As

soci

ated

with

Dom

estic

Ani

mal

s

Hos

tCh

ewin

g Lo

use

Suck

ing

Lou

se

Bird

sM

enop

on s

pp. (

poul

try)

Gon

oide

s sp

p. (

poul

try)

Col

umbi

cola

spp

. (pi

geon

s)

Non

e

Cat

sFe

licol

a su

bros

tratu

sN

one

Dog

sTr

icho

dect

es c

anis

Lino

gnat

hus

seto

sus

Swin

eN

one

Hae

mat

opin

us s

uis

Shee

pD

amal

inia

(=

Bov

icol

a) o

vis

Lino

gnat

hus

peda

lis (

also

goa

ts)

Lino

gnat

hus

ovill

us (

also

goa

ts)

Goa

tsD

amal

inia

(=

Bov

icol

a) c

apra

e D

amal

inia

(=

Bov

icol

a) li

mba

taLi

nogn

athu

s st

enop

sis

Lino

gnat

hus

afric

anis

Hor

ses

Dam

alin

ia (

=B

ovic

ola)

equ

iH

aem

atop

inus

asi

ni

Cat

tleD

amal

inia

(=

Bov

icol

a) b

ovis

Hae

mat

opin

us e

urys

tern

us

Lino

gnat

hus

vitu

liSo

leno

pote

s ca

pilla

tus

Rats

/mic

eN

one

Poly

plax

spi

nulo

sa/P

olyp

lax

serr

ata

Gui

nea

pigs

Glir

icol

a po

rcel

li G

yrop

us o

valis

Non

e

Ger

bils

Non

eH

oplo

pleu

ra m

erid

ioni

dis

Trichodectes canis is an intermediate host of Dipylidiumcaninum; Linognathus setosus is an intermediate hostfor Acanthocheilonema reconditum; Haematopinus suistransmits swine pox and probably Eperythrozoon.

Diagnosis

Lice and their eggs can be detected through carefulexamination of hair or feathers and are easily seen withthe naked eye. A hand-held magnifying lens may assist intheir visualization.


Dogs and cats: carbaryl shampoos, sprays, or dips, appliedin two treatments at 1 week intervals, are effective.

Beef and nonlactating dairy cattle: numerous sprays,dips, and pour-ons are available for use against lice as areinsecticidal ear-tags. Macrolide injectibles and pour-onshave excellent activity against anopluran infestations andpour-ons also work against mallophagans. If a herd has ahistory of infestation, fall treatment is recommended toavoid winter increase in lice populations. Beware of poten-tial host-parasite reactions to cattle grubs that may be con-currently in the esophagus or spinal canal (see Hypoderma).

Lactating dairy cattle: a few compounds that can beapplied as sprays or used in back rubbers or dust bags areavailable for this group of animals. Eprinomectin is alsoapproved and has no withdrawal time.

Arthropods 31

Pigs: injectible or premix formulations of avermectins orpour-on organophosphates are available for lice control.

Horses: two spray applications of coumaphos 2 weeksapart are effective. Dusting horses with a mixture of rotenoneand a synergized pyrethrin in winter may be less stressful.

Fleas (Insecta)Adult fleas are wingless, laterally compressed insects withpowerful hind legs allowing them to jump great dis-tances. They have piercing-sucking mouthparts thatenable them to feed on a hosts blood by piercing ablood vessel and imbibing the blood from the lumen.

Life Cycle

Complex metamorphosis with egg, maggot-like lar-val stages, pupa, and adults.

Adults are parasitic; other stages are found primarilyin the hosts environment.

Separate sexes with adult females laying small (about0.5 mm long), oval eggs on the host or in the envi-ronment.

Larvae hatch from eggs; three larval stages growingfrom about 2 mm to 5 mm in size, white, turningbrown after feeding (primarily on flea feces).

Third larval stage pupates; pupal stage is stage most resis-tant to environmental stress and chemical control efforts.

32 Arthropods

Heat, carbon dioxide, and movement stimulateadults to emerge from pupae.

Fleas tend to survive best in humid conditions.

Fleas Encountered in North America

CTENOCEPHALIDES FELIS AND CTENOCEPHALIDES CANIS Parasitize a wide variety of mammals; will feed on humans.

Ctenocephalides felis is the most commonly encountered fleaof cats and dogs.

Generally distributed throughout the United States, par-ticularly prevalent in humid areas.

Life cycle can take as little as 3 weeks or as long as 20months.

Feeding causes irritation resulting in the animal bit-ing and scratching; can cause anemia in very heavyinfestations.

Some animals become sensitized to the salivarysecretions resulting in an intensely pruritic reaction(flea-bite hypersensitivity or flea allergy dermatitis).

Intermediate host for Dipylidium caninum, Acan-thocheilonema reconditum; transmits Bartonella henselae(cat scratch fever).

ECHIDNOPHAGA GALLINACEA (STICKTIGHT FLEA) Parasitize poultry and other domestic birds; will feed

on dogs, cats, rabbits, horses, and humans.

Arthropods 33

Present in United States as far north as Kansas andVirginia.

Life cycle completed in 3060 days.

Females remain attached at site of feeding; causesswelling and ulceration; if near eyes, lesions maycause blindness.

XENOPSYLLA CHEOPIS (ORIENTAL OR TROPICAL RAT FLEA) Parasitize rats; will feed on humans.

Present in United States as far north as the northern-most states.

Life cycle completed in as little as 3 weeks.

Primary importance is as vector of plague (Yersinia pestis).

PULEX IRRITANS (HUMAN FLEA) Parasitize humans; will feed on dogs, cats, pigs, and

rats.

Life cycle takes about 1 month to complete.

This is a human parasite capable of transmittingplague; when recovered from a pet, must tactfullyexplain to the owners they are the reason the animalhas fleas.


Dogs and cats: lufenuron, fipronil, and imidaclopridhave dramatically changed flea control. All can be

34 Arthropods

administered at monthly intervals although lufenuronalso has a long-acting injectible formulation providingaction longer than a 1-month duration. Lufenuron doesnot kill adult fleas, but prevents eggs from hatching.Because the vast majority of all fleas are found in theenvironment as eggs, larvae, or pupae, environmentalcontrol should be considered in flea control programswith these or any other products. Numerous over-the-counter products are available as shampoos, collars, ortopicals, which provide adequate control when com-bined with proper environmental control programs.

Myiasis-Producing Flies (Insecta)The larvae of certain dipterans are capable of developingin the tissues of many domestic animals. This results in acondition called myiasis. There are two types of myiases:(1) facultative myiasislarvae are free-living, but canbecome parasitic under certain conditions; and (2) obligatory myiasislarvae are always parasitic, i.e., withouta proper host, the flies cannot complete their life cycle.

Life Cycle

Complex metamorphosis with egg, larval stages(instars), pupa, and adults.

Separate sexes with adult females laying eggs or lar-vae on host or in environment.

Larvae hatch from eggs; three larval stages (maggots).

Arthropods 35

Third larval stage pupates with adults emergingfrom pupae.

Obligatory Myiasis-Producing Flies

Adults of the obligatory myiasis-producing flies tend toresemble honeybees. They have only vestigial mouthpartsand, therefore, do not feed. They are quite annoying totheir hosts as the females buzz around the animal, layingher eggs. These flies are extremely host- and site-specific.Because they are so specific, the third-stage larvae can beprovisionally identified to genus based on host and sitealone. However, first- and second-stage larvae must be dif-ferentiated from larvae of the facultative myiasis- producing flies, particularly if in an abnormal host.

OESTRUS OVIS (SHEEP NASAL BOT) Females fly around nostrils of sheep and goats during

the hottest part of the day; deposit tiny, white to yellow,first-stage larvae; crawl into nasal sinuses, and developinto large (3 cm), dark brown third-stage larvae.

Third-stage larvae crawl out of the nostrils or aresneezed out; pupate in the ground; adults emerge36 weeks later; if begin pupating in fall, pupateoverwinter and adults emerge in spring; larvae canalso overwinter in nares of host.

Larvae produce a purulent rhinitis or sinusitis leading tohead shaking, restlessness, snorting; may lead to dam-age of cribriform plate and subsequent brain injury.

36 Arthropods

Diagnosis based on seeing large, dark brown larvaedropping out of nostrils; postmortem diagnosisachieved by sawing skull in half longitudinally, rins-ing key areas with water, and examining the rinsingsfor larvae with a magnifying lens.

Ocular myiasis of humans has been reported.

GASTEROPHILUS (OR GASTROPHILUS) SPP. (HORSE STOMACH BOT)

Three species in horsesG. nasalis, G. hemorrhoidalis,G. intestinalis.

Adult females attach elongate, operculated eggs tohairs of the intermandibular space (G. nasalis), thelips (G. hemorrhoidalis), or forelegs and shoulders (G.intestinalis) during late summer and early fall.

Eggs around the mouth hatch spontaneously; thoseelsewhere hatch in response to sudden warmth pro-vided by the breath of the horse.

Larvae penetrate and migrate in oral mucosa andtongue; eventually reach the stomach or duodenumand attach to the wall.

Third-stage larvae pass out in feces in spring; pupatein the soil for 39 weeks.

Generally considered benign parasites except forthe annoyance associated with the adults; mucosaland submucosal inflammation and mucosal ulcera-tion of the duodenum has been associated withinfections of G. nasalis in ponies.

Arthropods 37

Diagnosis is based on seeing eggs attached to hairsor distinctive third-stage larvae in feces; one can alsofind larvae at necropsy; usual attachment sites arethe first ampulla of the duodenum for G. nasalis, thenonglandular part of the stomach at the margo pli-catus or in the saccus cecus for G. intestinalis, theduodenum and rectum for G. hemorrhoidalis.

HYPODERMA SPP. (CATTLE GRUBS; HEEL FLIES) Two species infesting cattle and bisonH. bovis

(northern cattle grub), H. lineatum (common orsouthern cattle grub).

Hypoderma lineatum is present in the southern UnitedStates; both species are present in the northernUnited States and into Canada.

Entire life cycle of both species takes about 1 year tocomplete.

Adult H. lineatum becomes active with the start ofwarm weather, remaining active for about 2 months;H. bovis becomes active about the time H. lineatumstops, remaining active into summer.

Larvae hatch spontaneously, crawl down hair shaft,penetrate skin, and migrate through the subcuta-neous tissues.

Larvae, in 45 months, come to rest in either thesubmucosal connective tissue of the esophagus (H.lineatum) or the epidural fat (H. bovis); remain therefor about 3 months.

38 Arthropods

Resume migration to subcutaneous tissues of theback, cut breathing holes and increase in size as theydevelop to the third-stage larvae.

When fully developed, larvae exit through breathingholes, fall to ground, and pupate with adult fliesemerging in 45 weeks.

Egg-laying activity disturbs animals; they run aboutaimlessly (gadding) in an attempt to escape the flies;results in loss of production.

Larval infestation leads to carcass damage and dam-age to hide from the breathing holes; if animals aretreated when larvae are in resting sites (esophagus,spinal canal), signs of bloat/choke or central ner-vous system disease can result.

Diagnosis is made by finding either the eggs on hairsof the legs or the larvae in the back.

Infestations of horses and humans have beenreported, although rare.

COCHLIOMYIA HOMINOVORAX(AMERICAN PRIMARY SCREWWORM)

Only fly in North America attracted to unconta-minated skin wounds of domestic animals; willinfest any living warm-blooded animal (includinghumans) with a wound.

Adult females lay many eggs in batches of 15400 atthe edge of wounds.

Arthropods 39

Larvae hatch spontaneously and enter wound feed-ing on secretions and living flesh; become third-stage larvae in 57 days.

Larvae drop to ground, burrow in soil and pupate;adults emerge in one to several weeks.

Life cycle can be completed in as little as 24 days; lar-vae cannot overwinter where soil freezes.

Fatal if not treated; can kill a full-grown steer in 57days.

Massive eradication efforts used insecticidal treatmentof all infested animals and release of sterile flies to elim-inate this parasite from the United States and Mexico.Because females mate once and the wild population ofthe fly is relatively small, release of billions of sterilemales swamps the population and significantly reducesthe chance of a successful mating.

Occasionally reenters the United States in importedanimals; larvae encountered in wounds (particularlyof imported animals or animals in border areas withMexico) must be differentiated from facultative myi-asis-producing flies. If encountered, it must bereported to state and federal authorities.

CUTEREBRA SPP. Primarily parasites of rabbits and rodents; will infest

dogs and cats; although rare, most frequent cause ofendemic human myiasis in North America.

40 Arthropods

Adult females lay eggs near entrances to burrows oralong rabbit runs.

Larvae hatch in response to presence of animal,crawl into fur, and enter subcutaneous tissues of hostthrough natural body openings.

Cut breathing holes and develop to large (up to 3cm), black third-stage larvae in subcutaneous cysts.

In dogs and cats, generally found in neck and headregion in late summer and early fall; also found inaberrant sites including anterior chamber of the eyeand the brain.

Generally benign unless secondary bacterial infec-tion of cyst occurs or larvae migrate to aberrant sites.

Diagnosis is based on finding characteristic cysts withbreathing holes in which second- or third-stage lar-vae are usually present.

Facultative Myiasis-Producing Flies

GENERA OR SPECIES INVOLVED Lucilia (green or copper bottle flies)

Phoenicia (green bottle flies)

Phormia (black blow flies)

Calliphora (blue bottle flies)

Sarcophaga (flesh flies)

Cochliomyia macellaria (secondary screwworm)

Arthropods 41

IMPORTANCE Normally, adults lay eggs in carrion or feces; also

attracted by suppurative wounds, necrotic areas, skinsoiled with urine, feces, or vomitus (bacterial growthgenerates odors attractive to flies); condition calledfly strike or strike.

Females feed and lay eggs; larvae hatch; feed onnecrotic debris and exudates.

Larvae can cause further damage; some may invadehealthy subcutaneous tissue producing large cavitiesor tunnels; host becomes anorexic and weak.

Infestation can lead to death as a result of sep-ticemia, toxemia, or shock.

DIAGNOSIS Diagnosis of maggot infestation is not diffi-cult because the larvae are easily observed in the wound orwithin the hair coat. Species diagnosis, however, is depend-ent on morphologic characteristics of the larvae, particu-larly of the spiracular plates on the posterior end of thelarvae. Depending on the situation, larvae may need to bedifferentiated from those of Cochliomyia hominivorax. Inthat case, collect larvae, preserve in 70% ethanol, and sub-mit to proper authorities for identification.


For bots of sheep, horses, and grubs of cattle, avermectins areeffective. Treatment of cattle should be done immediatelyafter fly season ends but before the larvae reach the esopha-

42 Arthropods

gus or spinal cord; destruction of larvae in these tissuescauses severe inflammatory reactions and clinical signs cor-responding to the locality of the larvae. The danger periodfor treatment is estimated to be 68 weeks before the larvaeappear in the back, which occurs around mid-September inthe southern United States, late December in areas such asOhio, and late January in the more northern areas of theUnited States. Although adverse reactions are considered tobe rare occurrences these days, they must still be kept inmind in designing parasite control programs for cattle.

Infestations of C. hominivorax are reportable; shouldit occur, treatment and control requirements will be out-lined at that time.

Treatment of Cuterebra consists of manual extractionof the larva.

Treatment of facultative myiasis infestations includesdebriding area, applying appropriate insecticides, and, ifpresent, treating secondary bacterial infections.

Keds (Insecta)This is a group of dorso-ventrally flattened insects thatmay or may not have wings. Although there are numer-ous species of keds in North America, only one is gener-ally encountered in veterinary medicine.

Melophagus ovinus (Sheep Ked)

Entire life cycle spent on sheep or goats; transmis-sion is by direct contact although fed females maylive up to a week off the host.

Arthropods 43

No eggs present on host; larvae retained inabdomen until ready to pupate; time until adultemergence depends on ambient temperature.

Most numerous in cold months (fall, winter) withfewer present during warm months; more prevalentin northern United States and Canada.

Feed on blood which may cause anemia; bites arealso pruritic leading to biting, scratching, and rub-bing which damages wool; ked feces stains wool,decreasing value.

Coumaphos, malathion, and other insecticides areeffective against this parasite.

Biting Gnats and Mosquitoes (Insecta)These dipteran insects are periodic parasites; that is, theonly role vertebrate hosts have in the insects life cycle isas a food source for the adult females. However, theseinsects have a primary role as biological vectors of variousdisease-causing agents. Because the insects are only peri-odic parasites, they are usually not found on the animals.

Life Cycle

Complex metamorphosis with egg, up to five larvalstages, pupa, and adults.

Separate sexes with adult females laying eggs inaquatic or semi-aquatic habitats.

44 Arthropods

Larvae hatch from eggs; final larval stage pupates;adults emerge.

Adult females need bloodmeal for egg development;males do not feed on blood.

Simulium spp. (Black Flies; Buffalo Gnats)

Tiny flies (16 mm long) that tend to swarm;require well-aerated water for eggs; limits geo-graphic distribution to areas of swiftly runningwater.

Serrated, scissor-like mouthparts; lacerates tissue toform a pool of blood; bites very painful; ears, neck,and abdomen are favored feeding sites.

Swarming and biting can cause annoyance, resultingin decreased production in livestock.

Transmit Leucocytozoon spp. (hemoparasites of birds),Onchocerca gutterosa.

Culicoides spp. (No-See-Ums, Biting Midges)

Tiny gnats (13 mm long); habitat requirementsvary with species; strong fliers that tend to remainclose to breeding grounds; active at dusk or dawn.

Bites are very painful; favored feeding sites are eitheron dorsal or ventral aspect of host, depending onspecies involved.

Bites cause annoyance.

Arthropods 45

Allergic dermatitis in horses; begins as discretepapules on dorsum; areas of alopecia form as hairmats, crusts, then falls off; intensely pruritic leadingto scratching and rolling behavior which may lead toinjury or secondary infection.

Transmit bluetongue virus, Onchocerca cervicalis, Haemo-proteus, and Leucocytozoon spp. (hemoparasites of birds).

Anopheles spp., Aedes spp., Culex spp. (Mosquitoes)

Small flies (36 mm long) that tend to swarm; layeggs on water or in dry places that flood periodically;complete entire life cycle in as little as 12 weeks.

Have piercing-sucking mouthparts; pierces blood ves-sel and feeds from the lumen; bites can be painful.

Swarming and biting can cause annoyance leading todecreased production in livestock; rarely causes anemia.

Transmit eastern and western equine encephalitis,Plasmodium species (malaria), Dirofilaria immitis.


Because these pests are not found on the host exceptwhen feeding, insecticidal treatment is ineffective unlessrepeated every few days; this becomes too expensive andimpractical. Consequently, control is aimed at killingpre-adult stages.

46 Arthropods

Horse Flies, Deer Flies (Insecta)Like mosquitoes and biting gnats, horse flies and deerflies are periodic parasites in which only the adultfemales feed on blood.

Life Cycle

Complex metamorphosis with egg, larval stages,pupa, and adults.

Separate sexes with adult females laying eggs inaquatic or semi-aquatic habitats.

Larvae hatch from eggs, drop into the water or mud;first- and second-stage larvae do not feed; later stagesfeed on insect larvae, snails, young frogs, organicmatter, etc.; in temperate regions, larvae may over-winter and pupate the following spring.

Pupae are found in dry soil; adults are active onlyduring warmer months in temperate regions.

Adult females need blood for egg development;interrupted feedersfeeds several times in multiplesites on one or more hosts until replete; preferredfeeding sites are ventral abdomen, legs, neck, with-ers; prefers feeding on larger animals.

Genera Involved

Tabanus (horse flies)

Chrysops (deer flies)

Arthropods 47

Importance

Large flies (up to 3.5 cm with horse flies being big-ger than deer flies).

Bite very painful; scissor-like mouthparts lacerate tissueto form pool of blood; bite causes restlessness, annoy-ance, avoidance behavior, which interferes with grazingand resting resulting in decreased production.

Mechanical vectors of anaplasmosis, anthrax, equineinfectious anemia virus.

Tabanus spp. are intermediate hosts for Elaeophoraschneideri (arterial worm of deer, elk, sheep).


Difficult to kill or repel. Flies rarely enter roofed areas sostabling during hours of peak fly activity helps. Keepinganimals inside a fence 2.4 m in height with a 0.6 cm meshhelps reduce the attack rate. Keep grazing animals awayfrom the edge of wooded areas also helps reduce theattack rate.

Stable Flies, Horn Flies, Face Flies (Insecta)These flies are periodic parasites with different feedinghabits. Both male and female stable and horn flies feedon blood whereas only female face flies feed on mucus,saliva, and tears.

48 Arthropods

Life Cycle

Complex metamorphosis with eggs, larvae, pupae,and adults.

Separate sexes with adult females laying eggs indecaying organic matter (stable fly) or fresh cowmanure (horn fly, face fly).

Larvae hatch from eggs; final larval stage pupates;adults emerge.

Stomoxys calcitrans (Stable Fly)

Flies similar in size to house fly (67 mm long);piercing-sucking mouthparts.

Distributed primarily in central and southeasternUnited States.

Horse preferred host, but will feed on most domes-tic animals and humans; feed 12 times per daydepending on ambient temperature; feed primarilyon legs and flanks of cattle and horses, ears of dogs,ankles of humans.

Bites are painful; annoyance can lead to decreasedproduction in livestock.

Mechanical vectors of anthrax and equine infectiousanemia virus; intermediate host for Habronemamicrostoma (stomach nematode of horses).

Arthropods 49

Haematobia irritans (Horn Fly)

Dark-colored, small flies (36 mm long); piercing-sucking mouthparts.

Distributed throughout North America.

Feed on cattle; rarely on horses, sheep, dogs.

Adults spend most of life on host, leaving only to layeggs; adults cluster on shoulders, back, and sides; ifambient temperature < 70F, cluster around base ofhorns; if quite hot, cluster on ventral abdomen.

Irritation associated with feeding activities results inlost beef and/or dairy production; of all blood-suck-ing flies in the United States, this fly is most respon-sible for reduced weight gains and milk production.

Intermediate host for Stephanofilaria stilesi (filaridnematode of cattle).

Can cause a focal, midline dermatitis in horses.

Musca autumnalis (Face Fly)

Medium-sized flies (about 6 mm long); spongingmouthparts.

Generally distributed in North America except forthe southwestern United States; adults will hibernatein large groups inside buildings.

Feed on all types of livestock, horses, and bison.

Flies feeding activity is irritating to the host; canlead to decreased production.

50 Arthropods

Mechanical vectors of infectious keratoconjunctivitis(pinkeye).

Intermediate host for Thelazia spp. (eyeworms) ofcattle.


Treatment with insecticides is possible; read the labeland follow directions carefully. Insecticidal ear tags canbe effective fly control aids. Pour-on avermectins areeffective against horn flies

Arthropods 51

3Introduction to the Endoparasites

Endoparasites are those parasites that live within the bodyof the host. There are four major groups of endoparasitesnematodes, acanthocephalans, platyhelminths (trematodesand cestodes), and protozoans. Table 31 provides distin-guishing characteristics of the helminthic parasites.

NematodesAppearance and Morphology

Variable length, 1 mm to several meters.

Body covered with cuticle, may form specializedstructures (e.g., alae).

Usually sexually dimorphic with males smaller thanfemales.

53

54 Introduction to the Endoparasites Ta

ble

31

Cha

ract

eris

tics

of th

e M

ajor

Hel

min

th G

roup

s

Char

acte

rist

icP

hyl

um

Nem

ath

elm

inth

esA

can

thoc

eph

ala

Pla

tyh

elm

inth

es

Cest

odes

Trem

atod

es

Body

sha

peRo

und,

elo

n-ga

te, g

ener

ally

ta

perin

g at

bo

th e

nds,

not

se

gmen

ted

Roun

d, e

lon-

gate

, ant

erio

r w

ith s

piny

pr

obos

cis,

ap

pear

s to

be

segm

ente

d

Dor

so-v

en-

trally

at

-te

ned,

el

onga

te,

segm

ente

d

Dor

so-v

en-

trally

at

-te

ned,

leaf

-sh

aped

, not

se

gmen

ted

Coe

lem

Pseu

doco

elPs

eudo

coel

Acoe

lom

ate

Acoe

lom

ate

Dig

estiv

e tra

ctC

ompl

ete

(mou

th,

esop

hagu

s,

inte

stin

e, a

nus)

Abse

ntAb

sent

Inco

mpl

ete

(mou

th,

esop

hagu

s,

inte

stin

e)

Sexe

sD

ioec

ious

(s

epar

ate

sexe

s)

Dio

ecio

usM

onoe

ciou

s (h

erm

aphr

o-di

tic)

Mon

oeci

ous

(exc

eptio

ns)

Classification

Nematodes are divided among two classes: the Secer-nentea and the Adenophorea. The Adenophorea con-tains the whipworms, capillarids, and Trichinella spiralis,while the Secernentea contains the remainder of the par-asitic nematodes. Numerous advancements have beenmade in our understanding of the relationships of manyof these parasites. As a consequence, some nematodeshave been reassigned to different genera (Table 32).While some consider presenting current and future vet-erinarians with proper taxonomic nomenclature to beimpractical, others consider not to do so to be a disser-vice to their continuing education and development.Therefore, those changes in species level nomenclaturewhich have achieved general acceptance among the sci-entific community are presented herein. Tables 33, 34,35, 36, and 37 present the orders, families, andspecies of the parasitic nematodes by host group.

Life Cycle

All nematodes, whether parasitic or free-living, havethe same stages in the life cycle: egg, four larvalstages (L1 molts to L2 molts to L3 molts to L4), imma-ture adult (sometimes called L5), which matures intoadult.

Stages occurring in the external environment are sub-jected to stresses (temperature, desiccation, sunlight,etc.) that may kill or delay development (develop-

Introduction to the Endoparasites 55

56 Introduction to the Endoparasites

Tab

le 3

2Re

clas

sic

atio

n of

Som

e Pa

rasi

tes

Impo

rtan

t to

Vete

rinar

y M

edic

ine

Old

Nam

eN

ew N

ame

Inte

rmed

iate

/Pa

rate

nic

Hos

tD

en

itiv

e H

ost

Site

of

Infe

ctio

n

Cap

illar

iaae

roph

ilaEu

cole

usae

roph

ilus

Earth

wor

mC

anid

s, fe

lids,

m

uste

lids

Lung

s

Cap

illar

ia

bhm

iEu

cole

us

bhm

iN

one

know

nFo

x, d

ogN

asal

, par

ana-

sal s

inus

es

Cap

illar

ia p

lica

Pear

sone

ma

plic

aEa

rthw

orm

Can

ids,

mus

-te

lids

Urin

ary

blad

der

Cap

illar

ia

felis

cati

Pear

sone

ma

felis

cati

Earth

wor

mFe

lids

Urin

ary

blad

der

Cap

illar

ia

puto

riiAo

ncho

thec

apu

torii

Earth

wor

mM

uste

lids,

ra

ccoo

n,

pig,

cat

Stom

ach,

smal

l in

test

ine

Cap

illar

ia b

ovis

Aonc

hoth

eca

bovi

sN

one

know

nC

attle

Smal

l int

estin

e


Cap

illar

iaan

nula

tus

Euco

leus

an

nula

tus

Earth

wor

mC

hick

ens,

w

ild g

ame

bird

s

Esop

hagu

s,

crop

Cap

illar

ia

cont

ortu

sEu

cole

us

cont

ortu

sN

one

orea

rthw

orm

Wid

e va

riety

of

bird

sEs

opha

gus,

cr

op,

mou

th

Cap

illar

ia

obsi

gnat

aB

arus

capi

llaria

ob

sign

ata

Non

eW

ide

varie

ty

of b

irds

Smal

l int

estin

e

Dip

etal

onem

a re

cond

itum

Acan

tho-

chei

lone

ma

reco

nditu

m

Flea

s, li

ceC

anid

sSu

bcut

aneo

us

tissu

es

Toxo

cara

cat

iTo

xoca

ram

ysta

xRo

dent

sFe

lids

Smal

l int

estin

e

Ost

erta

gia

circ

umci

ncta

Tela

dors

agia

circ

umci

ncta

Non

eRu

min

ants

, es

peci

ally

sh

eep

Abom

asum

Bab

esia

equ

iTh

eile

ria e

qui

Ixod

id ti

cks

Hor

ses

Red

bloo

d ce

lls


ble

33

Cla

ssi

catio

n of

Nem

atod

es E

ncou

nter

ed in

Pig

s

Clas

sO

rder

Fam

ily

Spec

ies

Sece

rnen

tea

Rhab

ditid

aSt

rong

yloi

dida

eSt

rong

yloi

des

rans

omi

Stro

ngyl

ida

Tric

host

rong

ylid

aeH

yost

rong

ylus

rub

idus

St

rong

ylid

aeO

esop

hago

stom

um d

enta

tum

; O

. bre

vica

dum

Sy

ngam

idae

Step

hanu

rus

dent

atus

M

etas

trong

ylid

aeM

etas

trong

ylus

apr

i; M

. pud

en-

dode

ctus

; M. s

alm

i As

carid

ida

Asca

ridiid

aeAs

caris

suu

m

Spiru

rida

Spiro

cerc

idae

Asca

rops

stro

ngyl

ina

Phys

ocep

halu

s se

xala

tus

Aden

opho

rea

Enop

lida

Tric

hurid

aeTr

ichu

ris s

uis

Tric

hine

llida

eTr

ichi

nella

spi

ralis


Tab

le 3

4C

lass

ica

tion

of N

emat

odes

Enc

ount

ered

in H

orse

s

Ord

erFa

mil

ySp

ecie

s

Rhab

iditi

daSt

rong

yloi

dida

eSt

rong

yloi

des

wes

teri

Hal

icep

halo

bus

(=M

icro

nem

a) d

elet

rix*

Rhab

ditis

(=

Pelo

dera

) st

rong

yloi

des*

* Not

men

tione

d fu

rther

in th

is b

ook.

Stro

ngyl

ida

Dic

tyoc

aulid

aeTr

icho

stro

ngyl

idae

Dic

tyoc

aulu

s ar

nel

di

Tric

host

rong

ylus

axe

i St

rong

ylid

aeSt

rong

ylus

vul

garis

; S.

eden

tatu

s; S

. equ

inus

C

yath

osto

mum

spp

. and

ot

her s

mal

l stro

ngyl

es

Asca

ridid

aAs

carid

iidae

Para

scar

is e

quor

um

Oxy

urat

aO

xyur

idae

Oxy

uris

equ

i Sp

irurid

aH

abro

nem

atid

aeD

rasc

hia

meg

asto

ma

Hab

rone

ma

mus

cae;

H

. mic

rost

oma

Thel

aziid

aeTh

elaz

ia la

crym

alis

O

ncho

cerc

idae

Onc

hoce

rca

cerv

ical

is


Tab

le 3

5C

lass

ica

tion

of N

emat

odes

Enc

ount

ered

in R

umin

ants

Clas

sO

rder

Fam

ily

Spec

ies

Sece

rnen

taRh

abdi

tida

Stro

ngyl

oidi

dae

Stro

ngyl

oide

s pa

pillo

sus

Stro

ngyl

ida

Tric

host

rong

ylid

aeO

ster

tagi

a os

terta

gia;

* Te

lado

rsag

ia c

ircum

cinc

ta

Tric

host

rong

ylus

axe

i; T.

col

ubrif

orm

is

Hae

mon

chus

con

tortu

s;

H. p

lace

i C

oope

ria s

pp.

Mol

inei

dae

Nem

atod

irus

spp.

St

rong

ylid

aeO

esop

hago

stom

um r

adia

-tu

m; O

. ven

ulos

um;

O. c

olum

bian

um

Cha

berti

a ov

ina

Ancy

lost

omat

idae

Buno

stom

um

phle

boto

mum


* Sev

eral

oth

er s

peci

es o

f Ost

erta

gia

exis

t and

may

cau

se o

r con

tribu

te to

dis

ease

. N

ot m

entio

ned

furth

er in

this

boo

k.

Dic

tyoc

aulid

aeD

icty

ocau

lus

lar

ia;

D. v

ivip

arus

Pr

otos

trong

ylid

aeM

uelle

rius

capi

llaris

Pr

otos

trong

ylus

spp

. Sp

irurid

aTh

elaz

iidae

Thel

azia

skr

jabi

ni; T

. gul

osa

Gon

gylo

nem

atid

aeG

ongy

lone

ma

pulc

hrum

; G

. ver

ruco

sum

O

ncho

cerc

idae

Seta

ria la

biat

opap

illos

a O

ncho

cerc

a gu

ttero

sa;

O. l

iena

lis

Fila

riida

eSt

epha

nol

aria

stil

esi

Aden

opho

rea

Enop

lida

Tric

hurid

aeTr

ichu

ris b

ovis

; T. o

vis;

T.

skr

jabi

ni

Cap

illar

iidae

Aonc

hoth

eca

bovi

s


ble

36

Cla

ssi

catio

n of

Nem

atod

es E

ncou

nter

ed in

Dog

s an

d C

ats

Clas

sO

rder

Fam

ily

Spec

ies

Sece

rnen

tea

Rhab

ditid

aSt

rong

yloi

dida

eSt

rong

yloi

des

ster

cora

lis

Stro

ngyl

ida

Ancy

lost

omat

idae

Ancy

lost

oma

cani

num

; A.

tuba

efor

me;

A. b

razi

liens

eU

ncin

aria

ste

noce

phal

aM

olin

eida

eO

llula

nus

tricu

spis

* An

gios

trong

ylid

aeAl

euro

stro

ngyl

us a

bstru

sus

Angi

ostro

ngyl

us s

pp.*

Fila

roid

idae

Fila

roid

es o

sler

i; F.

hirt

hi*

Cre

noso

mat

idae

Cre

noso

ma

vulp

is*

Asca

ridid

aTo

xoca

ridae

Toxo

cara

can

is; T

. mys

tax

Asca

ridiid

aeTo

xasc

aris

leon

ina

Bay

lisas

caris

pro

cyon

is

Spiru

rida

Spiro

cerc

idae

Spiro

cerc

a lu

pi

Phys

alop

terid

aePh

ysal

opte

ra s

pp.

Thel

aziid

aeTh

elaz

ia c

alifo

rnie

nsis


* Not

men

tione

d fu

rther

in th

is b

ook.

Onc

hoce

rcid

aeD

irol

aria

imm

itis

Acan

thoc

heilo

nem

a re

cond

itium

Dra

cunc

ulid

aeD

racu

ncul

us in

sign

is

Aden

opho

rea

Dio

ctop

hym

ida

Dio

ctop

hym

a-tid

aeD

ioct

ophy

me

rena

le

Enop

lida

Tric

hurid

aeTr

ichu

ris v

ulpi

s; T

. cam

panu

la;

T. s

erra

ta

Cap

illar

iidae

Aonc

hoth

eca

puto

rii

Euco

leus

bh

mi;

Euco

leus

aer

ophi

lus

Pear

sone

ma

plic

a;

Pear

sone

ma

felis

cati


Tab

le 3

7C

lass

ica

tion

of N

emat

odes

Enc

ount

ered

in P

oultr

y an

d O

ther

G

allin

aceo

us B

irds

Clas

sO

rder

Fam

ily

Spec

ies

Sece

rnen

tea

Rhab

ditid

aSt

rong

yloi

dida

eSt

rong

yloi

des

aviu

m

Stro

ngyl

ida

Syng

amid

aeSy

ngam

us tr

ache

a H

eter

akid

aeH

eter

akis

gal

linar

um

Asca

ridiid

aeAs

carid

ia g

alli

Aden

opho

rea

Enop

lida

Cap

illar

iidae

Euco

leus

ann

ulat

us

Euco

leus

con

tortu

s B

arus

capi

llaria

obs

igna

ta

mental times presented throughout the book areminimum times required under optimal conditions).

For most parasitic nematodes, the third-stage larva isthe infective stage (i.e., the stage that initiates infectionin the definitive host); infective larvae cannot feed andare usually ensheathedthe third-stage larvae do notcompletely shed the cuticular sheath of the second-stage larvae until some point after being ingested; thesheath provides protection against adverse environ-mental conditions; after the infective L3 sheds thesheath of the L2, they are referred to as parasitic L3.

Transmission may be direct (no intermediate hostrequired) or indirect (intermediate host required orparatenic host involved).

Development to adulthood may proceed normallyor, under certain circumstances, larvae may arrestdevelopment and remain quiescient until reacti-vated at a later time.

Adults infect a variety of organs; larval migration may ormay not occur depending on species and site of infection.

Acanthocephalans (Thorny-Headed Worms)Appearance and Morphology

Variable length, 6 mm to 30+ cm.

Proboscis is retractable into body; body covered withtegument; absorbs nutrients.


Usually sexually dimorphic wi

Veterinary Parasitology- The Practical Veterinarian

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