Diagnosis of

External Parasites

Asst. Prof. Dr.Iman Daham Al-Maula

Department of Internal & Preventive Medicine

College of Veterinary Medicine

1: Many arthropods function indirectly in disease in

that transmit, but do not produce disease condition.

2: Some may inflict their injury by bit, stings, or

other activities and other species are parasites.

3: Some are both parasites and mechanical and or

biological vectors of disease.

4: To diagnose an ectoparasitic infestation the

technician must be able to collect the ectoparasites

and their, identify the organism involved.

Arthropods divided in to:

1- Arachnids

2- Insect

* Arachnids include:

A-Aragasidae

B-Ixodidae

C-Mite

Mite:

The common geniuses of the mites include:

Sarcoptes, Psoroptes, Chiropters, Notoedres, Otodectes, Demoded and

Ceyletialla.

* Definitive diagnosis of mite include condition may be made by finding

parasites or their eggs.

Because of the location of these organism intimately associated with or in the

skin, scrapings of

* The infected area must be made it is best to scrape at the edge of the lesion

rather than the

Center because organisms are more commonly found around the periphery

to make an

Adequate examination, the skin must be scraped even to draw blood .if tissue

is dry or scaly,

Use a small amount of oil or glycerin on the scraping instrument.

Diagnosis of mite by two techniques:

1- Direct methods:

2- Digestion-Concentration techniques.

* Direct methods:

Mix the scrapings with oil on a microscope slide. apply coverslip

and examination, if material

Is too dense for ready examine. Add one or two drops of a (10

percent solution of potassium hydroxide), allow to stand a few

minutes then examination.

This procedure will clear debris and mite, then parasites may be

seen more easily.

Digestion- concentration techniques:

1- mix scraping with -5-percent (KOH 5%)-digesting solution-use about -10-

volumes of solution To -1-volume of detritus.

2- heat gently in a beaker or flask covered by a funnel, the condensate should

return to the digesting solution.

3- when hair has dissolved, remove mixture from heat and allow to cooling.

4- centrifuge and discard supernatant fluid.

5- resuspend sediment in water and centrifuge again.

6- dicard supernatant fluid and examine sediment, if no parasites are found,

concentrate .

7- resuspend sediment in saturated sucrose solution.(concentration

solution)and centrifuge.

8- remove parasites from top of solution with a wire loop or other implement.

* Sarcoptes scabiei

Is a minute parasite, roughly circular in outline. All the legs of

both sexes are short and the third and fourth pairs do not project

beyond the margin of the body.

The females bear on either side

of the mid-line anteriorly three

short spines and posteriorly

six longer spines with bifid tips,

in addition to a few hairs.

* Life cycle:

The female burrows in to the skin and lays forty to fifty eggs, in

the tunnel it forms.

The eggs hatch in3-5 days

to produce a six legged

larva, larva development

the nymph , there are two

nymphal stages, nymphs

have four pair of legs no

genital aperture finally,

Male and female are

produced.

**Pathogenesis:

The parasites pierce the skin to suck lymph and may also feed

on young epidermal cells.

Their activities produce a marked irritation which causes intense

itching and scratching, which

Aggravates the condition. The resulting inflammation of the skin

is accompanied by an exudate

Which coagulates and forms crusts on the surface, proliferation of

connective tissue, with the result that the skin becomes much

thickened and wrinkled, there is a concomitant loss of hair which

may be very wide spread.

* Demodex. spp.

Demodex is very specialized group of parasitic mites, live in the

hair follicles and sebaceous glands of various mammals causing

démodé tic or follicular mange.

Occur on different species of

host, such as:

* Demodex canis.

* Demodex ovis.

* Demodex caprae.

* Demodex bovis

Demodex bovis

The parasites are elongate, they have head, thorax, which hears

four pairs of stumpy legs and elongate abdomen and the mouth

parts consist of paired pulps and chelicerae and an unpaired

hypostome.

* Life cycle:

Develop in the skin of the host

The larva has three pairs of legs

And three nymph stages.

* Pathogenesis:

The mite enters the hair follicles

and sebaceous gland, producing a

chronic inflammation with proliferation

and thickening of the epidermis and

loss of hair. A secondary bacterial

invasion usually by Staphylococci,

frequently takes and leads to the

formation of pustules or abscesses,

the infection may be spread by

wandering of the parasites. Connect

of different part of the body or wrong

treatment death is due to toxemia or

emaciation.

* Psoroptes:

This genus contains a number of parasite, unlike the species of

the Sarcoptidae are specific to their hosts. These parasites live on

the skin of the body well covered with hair or wool or in the ears of

their hosts.

Psoroptes ovis

Psoroptes equi

Psoroptes natalensis in cattle.

* Psoroptes ovis:

Is the cause of sheep scab, the parasite cannot be transmitted to

other species of animals. The mites are oval and a white body

with brownish legs, the larvae has three pairs of legs and the

other stages four pairs. The larvae has two long bristles on the

third pair, the nymph pubescent females and vigorous females

has bristles on the third pair and suckers on the fourth, the third

pair of the male is long and suckered, while the fourth pair is very

short and bears only hairs.

* Life cycle:

The eggs are laid on the skin at edges of the lesion and hatch

normally in 1-3 days- larvae- hatching nymph stages- male and

females. (Picture 3)

* Pathogenesis:

The mites puncture the

epidermis to suck lymph and

stimulate local reaction in the

form of a small inflammatory

swelling richly infiltrated with

serum. The latter exudes on the

surface and coagulates, thus

forming a crust. The altered

condition cause the wool to

become loose and to fall out or it

is pulled out by the sheep in

biting and scratching the lesion,

which itches severely.

B- Ixodidae:

There are two groups:

* Hard ticks

* Soft tick

Hard ticks of this family possess a hard chitinous shield or scutum

which extends over the whole dorsal surface of the male and

covers only a small portion behind the head in the larva, nymph

and female.

Life cycle:

The ixodidae laid their eggs under stones and clods of soil, the

eggs are small, The newly hatched larvae or seed tick climb on to

grass and wait there till a suitable host passes. After having

engorged the larvae moults and become a nymph, the nymph

engorged and moults to become an imago, after hardening of the

integument, and after copulation on the ground. On the host

females engorge, drop of and seek a sheltered spot to lay, the

males remain much longer on the host than the females.

According to the NO.of hosts ticks can be classified in to 3 groups:

* One-host ticks

* Two- host ticks

* Three- host ticks

* One host ticks:

All three instars engorged on the some animal, the two ecdyses

also taking place on the host.e. g:

Boophilus annulatus.

* Two host ticks:

The larva engorges and moults on the host and the nymph drops

off after also a having engorged, it moults in the ground and the

imago seeks a new host. e. g Rhipicephalus bursa.

* Three host ticks:

These require a different host for every instar they drop off each

time after having engorged and moult on the ground. E. g Ixodes ricinus. (picture-4).

* Insects:

Like mite and ticks also belong to the phylum Arthropods- all

insects have bodies composed of three parts:

1- Head. 2- Thorax (which bears the legs). 3- Abdomen.

* Lice:

Are wingless, dorsoventrally flattened, and divided in to two types.

A- Mallophaga, biting or chewing lice.

B- Anoplura, sucking lice.

Lice and their eggs on large mammals may be detected by visual

examination, a magnifying lens or dissecting microscope will aid

the observation.

* Effects of Lice on their host.

1- The chief effects of lice on their hosts are due to the irritation

they cause.

2- They are most numerous in the winter, possibly because of

longer hair on the host coat, close contact of animals and also

lack of general vigour.

3-The host become restless and do not feed or sleep well and

they may injure themselves or damage their, feathers, hair or wool

by biting and scratching the part of their bodies irritated by lice.

4- fall in The egg production of birds and milk production of cattle

5- Produce wounds or bruises on the animal.

6- In sheep the wool is damaged it is also soiled by the feces of

the lice.

Diagnosis:

Is easily made by finding

the lice, especially when

the animal is standing in

the sunlight.

* Fleas:

These are not only effects on their hosts, but as carriers of

disease, most important in dog, cat and poultry.

* Morphology:

Fleas are dark brown, wingless insects, with laterally compressed

bodies which have a glossy surface.

* Life cycle:

Both sexes are blood suckers, and only the adult are parasitic

Eggs- Larvae- Nymph- Adults.e. g. Ctenocephalides. This is only

important genus in the dog and cat. (Picture 6).

E. g: 1- Ctenocephalides canis

2- Ctenocephalides felis

**This two type occur in dog and cat.

Both species can act as intermediate hosts for the common

Tapeworm of dog and cat:

1- Dipylidium caninum

2- Dipetalonema reconditam

* Pathogenesis:

Hypersensitivity to the bites of fleas is a common problem in

dogs and cat. Aradioimmuno assay has been developed to detect

allergen-specific antibodies (IgE and IgG) in serum, but it is not

yet in general use. Dogs and cats parasitized by helminthes often

have high levels of IgE and that fact may complicate serological

assessment of fleas- induced hypersensitivity. The adult contains

the Cysticercoid. Bite causes in dog and cat Dermatitis.

*Larval flies:

The critical aspects of Myiasis, as to lesion and symptom, will

vary with the body part affected, species of fly involved, and No.of

Maggots present.

1- Intestinal myiasis: are not specific

2- Cutaneous myiasis: may present problems insofar as specific

diagnosis is concerned.

3- Nasal myiasis: may cause obstruction of the nasal passages,

severe irritation, and some cases facial edema.

4- Aura myiasis: particularly when the middle ear is involved,

may lead to brain damage.

5-Ophthalmo myiasis: will lead not only to severe irritation and

pain but sometimes to blindness.

Finding and identifying the larvae responsible maggots may be

removed from the lesion.

Although the wide variety of adults flies that may attack or worry

animals, several flies are common and serious parasites of

domestic animals. (Picture 7).

1- Oestrus ovis: the nasal bot of sheep and goats.

2- Hypoderma bovis: the warble fly of cattle.

3- Gastrophilius intestinals and Gastrophilus nasanlis: the

Horse stomach bots.

4- Cochliomyia hominivorax: the larvae of the Screw worm, if

collected in 70% alcohol for identification.