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6.02 Parasites - Internal

Parasitology

The study of organisms that live on or in other organisms to survive

Parasites – may invade internal or external parts of the animal

Most have one location they live in, and feed off the host Host – animal that is infected

Go through a life cycle: born as larvae grow and reproduce

Can invade digestive tract, skin, or muscles

Parasites

Endoparasites – live within the host Whipworms, hookworms, heartworms, coccidian,

tapeworms, and strogyles

Ectoparasites – live on the host Ticks, fleas, mites

Modes of Transmission

Direct – transmission occur when the parasite is passed directly from one host to another Animals ingest infected feces or vomit, parasites

enter skin through penetration, mothers pass it to offspring through placenta or milk

Indirect – transmission occurs when an animal ingests a paratenic host Paratenic host – animal that can harbor the

parasite without becoming infected. Parasite remains inactive until appropriate host ingests it Rodents, rabbits, birds, even flies

Damage Caused by Parasites

Ectoparasite

Damage and irritate skin

Cause restlessness, nervousness

Transmit infectious organisms

Draw blood

Endoparasite

Absorb food intended for host

Draw blood and lymph fluid

Damage tissue and cause internal bleeding

Create obstructions in intestines and circulatory system

Produce toxins

Internal Parasites

Occur in small and large animals

Many internal parasites invade the intestinal system causing vomiting and diarrhea

Diagnosed through fecal flotation

Roundworms (Ascarids)

Most common intestinal parasite in small and large animals

Most common internal parasite in puppies and kittens/often occur in young animals

Live in small intestines

Can lay up to 200,000 eggs a day

Diagnosed by finding eggs in feces Eggs are circular with dark circular centers

Roundworms – Life Cycle

Parasite enters body by direct or indirect means

Migrates through various organs to the lungs, and into trachea

From trachea it is swallowed and larva travel to small intestines where they mature to adults

Eggs are shed in the feces

Cycle begins again

Roundworms - Types

Toxascaris leonina Dog and cat Simplest life cycle Eggs hatch after ingested Eggs passed in feces After 3-6 days, they are infected in the environment Animals become infected if they eat something

contaminated with infected feces

Roundworms - Types

Toxocara canis Dog Complicated life cycle Hardy and resistant Animal can become infected by ingestion of eggs,

transport host, or by larvae entering animal while in uterus

Migrate through circulatory system Can encyst (become walled off or inactive) if enter

body tissues

Roundworm - Types

Toxocara cati Cat Similar to T. canis Infective eggs are swallowed; larvae hatch;

penetrate stomach wall Larvae migrate to liver, other tissues, and lungs

Roundworm - Types

Parascaris equorum In large animals

Swallowed in contaminated hay or water Young worms burrow through intestinal wall Mature in intestine and lay eggs that are passed in

feces

In small animals Infections will show signs of vomiting, diarrhea, and

bloated stomach Visible in feces

Roundworms – Clinical Signs

Small animal symptoms Vomiting, diarrhea, bloated stomach, visible

roundworms in feces, potbelly, coughing, anemia (in severe cases), dull coat

Large animal symptoms Abdominal pain (common cause of obstruction colic

in foals), coughing, diarrhea, visible roundworm in feces, potbelly, anemia (severe cases)

Roundworms - Zoonosis

Roundworms cause visceral larval migraines in humans

Tapeworms - Cestode

Common in both dogs and cats

Has a long, flat, segmented body

Head is called the scolex

Segments called proglottids Contain eggs and look like grains of rice when shed in

feces Can be seen around the anus of dogs or cats

Adults attach to wall of small intestines where they absorb nutrients

Feas are vectors for tapeworms so animals with a heavy flea infestation should be tested for tapeworm

Tapeworm - Types

Dipylidium caninum – dog and cat Can be up to 20” long Lives in small intestines

Taenia pisiformis – dog

Taenia taeniaeformis – cat

Tapeworm – Modes of Transmission/Clinical Signs

Modes of Transmission Indirect

Animals ingest a flea or other intermediate hosts such as rabbits, mice, or lice

Clinical Signs Poor hair coat, abdominal discomfort, visible

segments in feces

Tapeworm – Life Cycle

Intermediate host eats the eggs

Dog or cat eats intermediate host

Parasite larvae migrate to small intestines to mature

Ptoglottids are shed in feces

Life cycle begins again

Hookworms

Ancylostoma caninum

Destructive parasite of dogs and cats that feeds on wall of small intestines

Teeth-like structures or cutting plates – attach to wall of intestine and feed on animal blood

Parasite changes feeding sites frequently causing hemorrhaging that leads to anemia and protein loss

Death is common in untreated puppies

Hookworm – Life Cycle

4 – 6 weeks

Larvae are ingested, absorbed, or passed to the host by indirect means and migrate to lungs via bloodstream

From the lungs, larvae pass into trachea where they partially develop, coughed up and then swallowed to the small intestines

Larvae mature to adults, begin to feed, shed eggs in feces

Cycle starts again

Hookworm – Types/Modes of Transmission

Types Ancylostoma – common in warm climates Uncineria – common in northern U.S. & Canada

Modes of Transmission Direct

Ingestion, skin penetration, transmammary

Hookworm – Clinical Signs/Zoonosis

Clinical Signs Vomiting, diarrhea, anemia, weakness, black

darkened feces or blood in stool, dull coat, pale mucus membranes, anorexia

Cause cutaneous larval migraines in humans where larvae burrow through humans skin, most common in young children

Whipworm

Trichuris vulpis

Infect animals through ingesting contaminated food or water

Adults have whip-like shape

Attach to large intestines and cecum by threading their “whip” through intestinal lining

Very rare in cats

Adult whipworms are not visible in feces

Whipworm – Life Cycle

4 – 7 weeks

Eggs eaten by a host

Larvae hatch and begin their development in small and large intestines

Larvae mature to adults in cecum or large intestines

Eggs containing infective larvae are passed in feces

Cycle begins again

Whipworm – Types/Modes of Transmission

Types Trichuris vulpis

Modes of Transmission Direct

Ingestion of eggs

Whipworm – Clinical Signs

Diarrhea

Weight loss/emaciation

Possible blood in feces

Anemia

Dehydration

Death may occur in severe cases

Protozoa

Several different species commonly known as coccidian

Infection of protozoa is called coccidiosis

Coccidia infest walls of the intestines

Protozoa – Types/Modes of Transmission

Types Isospera – dog and cat Sarcocystis – dog and cat Toxoplasma gondii – cat

Modes of Transmission: Direct

Ingestion of eggs Indirect

Ingestion of infected animals

Protozoa – Life Cycle

Eggs or an infected animal ingested by host

Parasite’s cell wall is digested and enters epithelial cells of intestines where it begins to mature

During maturation, the eggs divide and develop into male and female

Fertilized female (oocyst) ruptures out of epithelial cell, passed in feces

Cycle begins again

Protozoa – Clinical Signs/Zoonosis

Clinical Signs: Diarrhea in puppies and kittens

Zoonosis Some species will cause disease in humans:

Toxoplasma gondii – causes abortions Giardia – “Beaver Fever” is transmitted in

contaminated food and water

Heartworm

Dirofilaria immitis

Affects heart and circulatory system of infected animals

Can affect dog, cats, ferrets, and even humans; although in humans the parasite is eliminated in the lungs

Adult heartworms live in the right side of the heart and in pulmonary artery

Worms are free living meaning they do not attach to the host’s body

Heartworm – Mode of Transmission

Mosquitoes are the vector

Heartworm is most prevalent in the southern states with warmer climates (larvae need warm temps to mature) and greater number of mosquitoes.

Heartworm – Life Cycle

Mosquito bites infected animal and picks up D. immitis microfilaria

Mosquito takes its next meal and microfilaria (larvae) passed to that animal

Microfilaria take 3 months to migrate to right side of heart During the 3 month migration, an infected animal shows no

clinical signs

Migration in the heart takes another 3 months

After 6-month migration and maturation period, adult heartworms begin producing microfilaria that are released into the bloodstream

Effects of Heartworm Disease

Damage to the pulmonary artery lining

Compromised blood flow

Fluid leaks from the lungs

Life span: Dogs – adults live about 5 years Cats – adults live only 1-3 years

Heartworms – Clinical Signs

Symptoms in dogs Dogs with a light infection may be asymptomatic,

but with increasing worms there will be exercise intolerance, difficulty breathing, deep cough, decreased appetite, weight loss

Symptoms in cats Typically show no signs, but may die suddenly Or may show signs similar to dogs

Heartworms - Diagnosis

Methods will be unsuccessful unless the disease has progressed at least 6 months since no adults are present until that time

Methods: Blood smear to look for microfilaria Antigen test – test for antigens produced by adult

females; there are many commercial tests available X-ray – look for enlarged heart and pulmonary artery

Heartworms - Treatment

Often dangerous

Possibility that the dog won’t survive treatment or adult worms will form a clot in arteries

Surgery can be done to remove adult worms

Two non-surgical methods often used in combination Using an arsenic compound to kill adults, however

arsenic could also kill the dog Use ivermectin to kill microfilaria

Prevention with monthly treatments is better way to manage heartworms

Strongyles

Common parasite of large animals

Bloodworms or redworms

Eggs in manure hatch into larvae

Larvae mature in the intestinal tract and can cause extensive damage to lining of blood vessels

Strongyles

Signs of large strongyles Weight loss, anemia, abdominal pain, and sudden death

Small strongyles do not migrate through tissues as large ones do Encysted larvae require special anthelmintic treatments to

kill

Signs: Diarrhea, weight loss, poor growth, poor coat quality,

abdominal pain