Clinical Parasitology

Infestation

the presence of ectoparasites on their host

Infection

the presence of endoparasites in their host

From which 6 groups do most of the important parasites that affect domestic animals come from?

insects, arachnids, nematodes, tapeworms, trematodes, and protozoans

Vector

an animal that transfers an infective agent from one host to another

Insect life cycle

four stages: egg, larva, pupa, adult

Arachnid life cycle

four stages: egg, larva, nymph, and adult

Ticks are an example of what kind of parasite?

an ectoparasitic arachnid

Which parasites are generally small, wormlike organisms covered by a tough skin called a cuticle?

nematodes (roundworms)

Nematode life cycle

3 stages: egg, four larval phases, and adult

What kind of parasites are nematodes?

endoparasites

Which parasites are flat, ribbonlike worms with no digestive tract?

Tapeworms (cestodes)

Describe parts of tapeworm

• scolex = head

• proglottids = many segments of body

Tapeworm life cycle

3 stages: egg, larva, and adult

All _______ are endoparasites, and as adults always live in host’s digestive tract.

tapeworms

Which parasites are flat, leaf shaped worms with a mouth and gut, but no anus?

Trematodes (flukes)

Parasitic trematode life cycle:

complex: egg, several larval stages (some of which are endoparasites of snails) and adult

Protozoans

large group of single-celled animals made up of many different types of organisms

• endoparasites as adults

Diagnostic stage of a parasite

the life-cycle stage the vet uses to identify the parasite that has infected an animal

What are the diagnostic stages for parasites in the gastrointestinal tract?

eggs of the worms and the cysts of the protozoa in the feces

What to look for to decide if what you are looking at is parasite eggs and not plant debris?

parasite eggs and cysts have a regular outline and will contain an embryo or cells

Nematode larvae can be distinguished in photos because:

they will have a head and tail and will contain an intestine + other organs

Describe eggs of Toxocara canis or Toxocara cati (look similar but cat one is smaller)

They have a rough shell and a brown central mass that fills most of the shell

Toxocara canis

roundworm of dogs

Describe Toxascaris leonina eggs comapred to Toxocara eggs

• surface is smoother and the central mass doesn’t fill all of the space in the shell as compared to Toxocara

• same color as Toxocara when unstained

Toxacaris leonina

an ascarid/roundworm that can be found in both dogs and cats

Describe Trichuris vulpis eggs

• It’s a symmetrical lemon-shaped egg with a plug at either end.

• The whipworm egg has a smooth shell and is about 80 μm long.

Trichuris vulpis

whipworm of dogs

Describe Eucoleus aerophilus eggs

• smaller egg, more oval, and less symmetrical than the whipworm (Trichuris vulpis)

• has rough, pitted shell

Eucoleus aerophilus

lungworm whose egg is found in both dogs and cats

Describe Ancylostoma eggs

egg has very thin shell and mass of cells in center

Ancylostoma

hookworm of dogs and cats

Identify the parasite, it is commonly found in the stomach contents of small animals.

Toxocara cati

- a common nematode w “wings” along the head, like other ascarids of dogs and cats.

Identify the parasite which is commonly found in the stomach contents of small animals.

Physaloptera

• stomach worm of dogs and cats

• unique head that looks like it has been pulled back into body, forming a collar

Which parasites are sometimes found during fecal exams of dogs and cats, when the feces is fresh?

larval nematodes such as

• Strongyloides stercoralis

• lungworms, such as Eucoleus aerophila

Which parasites are sometimes found during the fecal exams of dogs and cats, particularly in feces more than 24 hours old?

larval nematodes, specifically hookworm larvae which have hatched from their eggs

Identify the parasite and its characteristics

1st stage larvae of Strongyloides stercoralis

• nematode that lives in small intestine wall of dogs and cats

• tapered tail

• oval-shaped group of cells near center of worm

The larvae of FIlaroides is very similar to the larvae of which other parasite?

the larva of the cat lungworm Aleurostrongylus.

Identify the parasite and its characteristics:

first-stage larva of the dog lungworm Filaroides.

• very similar to the larva of the cat lungworm Aleurostrongylus.

• Both have a small notch in the tail (arrow) which allows you to tell them apart from Strongyloides

Why are the eggs of Dipylidium caninum distinctive?

bc they’re found in packets containing 10 to 30 eggs

Which animals is Dipylidium caninum seen in?

it is a common tapeworm in dogs, but also seen in cats

Taenia

tapeworms common in cats, but also seen in dogs

Which parasite does the egg belong to?

Taenia - tapeworms

In both Taenia and Dipylidium infections, the terminal segment of the worm is called the _____________, and contains the eggs. It drops off and passes out with the feces.

proglottid

Which part of Taenia and Dipylidium drop off and pass out with the feces?

proglottid (terminal segment of the worm)

Identify the parasite and which part it is, the arrows are pointing to its two genital openings:

Proglottids of Dipylidium caninum

Identify the parasite and which part it is, the arrows are pointing to its one genital opening:

Taenia taeniaeformis Proglottids

• cat tapeworm

Identify the parasite

cysts of Giardia, found in both dogs and cats and extremely small

Identify the parasite

oocyst of Isospora canis

• coccidian parasite of dogs

• one central mass in young cyst and 2 in older

Identify the parasite

oocyst of Toxoplasma gondii

• coccidian parasite of cats

• one central mass in young cyst and 2 in older

Trichomonas sp. has no cyst stage, how is this protozoan then diagnosed?

through a direct smear of diarrhea

Identify the parasite

Trichomonas sp.

• protozoan that lives in the large intestine of cats and dogs.

Which parasite is being described?

Lives in the large intestine of cats and dogs, measures 15 to 20 μm long and is pear-shaped. It has several flagella (hairlike projections) coming out of its front end and an undulating membrane running the length of the body (arrow).

Trichomonas sp.

Identify the parasite and describe where is it found/what it infects:

Babesia canis

• found in blood of small animals

• infects red blood cells

All bird red blood cells have a ________.

nucleus

Identify the parasite and describe where is it found/what it infects:

Haemoproteus sp.

• protozoan parasite that infects blood cells of birds

Which parasite is a nematode that lives in the hearts of dogs and causes serious disease?

Dirofilaria immitis

• heartworm found free in the blood of dogs

Identify the parasite

Dirofilaria immitis

• heartworm found free in blood of dogs (not in blood cells)

• When killed in formalin (part of the concentration process), these microfilaria have a straight or slightly curved body.

Identify the parasite

Acanthocheilonema reconditum

• filarial worm that can be found free in blood of dog

• a nematode which lives in skin and causes no disease

Which nematode lives in the skin of dogs and causes no disease, but looks similar to Dirofilaria immitis and is also found free in the blood?

Acanthocheilonema reconditum

Single-celled animal

Protozoan

Leaf-shaped worm with a mouth

Trematode

Flat, ribbonlike worm with no digestive tract

Tapeworm

Small, cylindrical worm covered with a cuticle

Nematode

Adult parasite with eight legs and two body parts

Arachnid

Adult parasite with six legs and three body parts

Insect

Myiasis

general term for disease caused by larval flies

Chewing/biting lice

have mouthparts made for chewing their food, feed on skin and hair

One-host tick

spends all three of its feeding stages on one host

Two-host tick

stays on one host for two of its life stages and then feeds on a second host during its third feeding life stage

three-host tick

feeds on three different hosts, one for each life stage.

Mites can cause a skin disease called ______

mange