Parasitology Review

Parasitology A PARASITE is an organism that lives

Inside a HOST(endoparasite) Or on a HOST(ectoparasite)

A HOST is any organism that another organism or bacteria lives in or on. Parasites benefit at the expense of the host. The host-parasite relationship may be benign,

irritating, or in many cases, pathogenic. Every animal is subject to parasitism by a number of

species

Parasite Examples

Parasite Negative Impact on Host Injury by entry Injury by migration Injury by residence Chemical or physiological injury Injury due to host reaction

Parasite Life Cycles

The life cycle is a never-ending chain of events that lead to the parasite constantly reproducing and re-infecting another animal.

There are two types of life cycles: Indirect - require different types of hosts or a vector

(intermediate host) for various stages of their life cycle. Direct - a life cycle in which a parasite is transmitted directly

from one host to the next without an intermediate host or vector of another species.

The Intermediate Host Required by some parasites

to complete their life cycle.

Advantages of an intermediate hosts include: increasing the spread of the parasite & protecting the parasite from spending too much time in the environment.

Types of Parasitism Facultative parasite- Able to live free living or

parasitic existence. Obligatory parasite- completely dependent on

host for existence. Aberrant parasite- found in locations in a host

where they don’t normally occur. Incidental parasite- host where does not normally

occur, generally not harmful . Periodic parasite- feeds on host but does not live

on them . Hyperparasite- parasite that parasitizes other

parasites.

Fecal Exam for Diagnosis of Parasites Can find eggs larvae, cysts and adult parasites in

feces. Examine feces grossly for consistency, color, blood,

mucus and parasites. May find parasites in GI tract (most common),

respiratory tract, reproductive tract, eyes, and skin. Fecal exams should always be done on freshest

samples possible. In large animals feces should be collected directly from

rectum. Samples not examined immediately should be

refrigerated.

Flotation Solutions

Flotation solution Specific gravity

Advantages Disadvantages

Sodium nitrate/fecasol

1.2 Floats common helminths and protazoa

Distorts Giardia cysts, not good for flukes, some tapeworms or nematodes

33% Zinc Sulfate 1.18 Preferred for Giardia and Lungworm

Not effective for tapeworm or flukes

Saturated Sodium chloride

1.2 Floats common helminthes and protozoa

Distorts Giardia cysts, not good for flukes, some tapeworms or nematodes

Saturated Magnesium sulfate

1.32 Floats common helminthes and protozoa

Distorts Giardia cysts, not good for flukes, some tapeworms or nematodes

Sheather’s sugar solution

1.25 Floats common helminthes and protozoa. Preferred for Cryptosporidium

Does not float most flukes, unusual tapeworms or nematodes, less sensitive for Giardia

Endoparasites Small Animals, Horse, Swine, and Ruminants

TrematodesCestodesNematodes Protozoans

Trematodes of Veterinary Significance Fasciola hepatica Paramphistomum cervi Paragonimus kellicotti

Examples of Common Endo- Parasites

A B C C C D

E F G

Your Turn – Complete The Life Cycle --Number 5 in the Discussion Forum

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Nematodes of Veterinary Significance Ascarids

Toxocara spp. Toxascaris spp. Ascaris spp. Parascaris equorum, oxyuris equi

Strongylus spp, Ancylostoma spp.,Bunostomum spp. Uncinaria

Syngamus spp. Oesophagostomum spp. Haemonchus spp. Ostertagia spp. Trichostrongylus spp.

Cooperia spp., Nematodirus spp, Dictyocaulus spp. Metastrongyloidea

Metastrongylus spp., Aelurostrongylus abstrusus

Heartworm Disease Dirofilaria immitis – Nematode Adult worms found in pulmonary artery and right

ventricles in dogs, cats and ferrets. Parasite has been known to be found in a variety of

ectopic sites. Clinical signs- Early infection may be asymptomatic.

Later disease will show weight loss, exercise intolerance coughing, advanced cases will show fever, ascites, cyanosis, collapse.

Cats clinical signs- May be asymptomatic, may have sporadic vomiting, cough, acute respiratory distress syndrome or sudden death.

Arthropods Parasites with jointed appendages or feet

Mites Sarcoptes scabei (scabies mites) Otodectes cynotis (ear mites) Demodex cani (hair follicle and sebaceous gland) Cheyletiella parasitivorax (walking dandruff mite) Trombicula (chiggers)

Ticks Soft ticks -- Argasidae Hard ticks – Ixodidae

Parasitic Insects

Fleas, Lice, and Flies

Fleas Lice-Mallophaga and Anoplura Flies-mosquitos, sandflies, biting flies, bot flies

Fleas Blood-sucking parasite

Dogs, cats, rodents, birds, people May cause anemia or flea-bite dermatitis (miliary

dermatitis) Ctenocephalides felis and C. canis

Intermediate host for other parasites Dipylidium caninum: tapeworm

Vector for disease Bubonic plague, tularemia

Flea Life Cycle

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