Veterinary Parasitology CH4 P2 - Nematodes of Ruminants and Other Animals

Part 2 of study material for Chapter 4 of Diagnostic Parasitology for Veterinary Technicians. For class BIO225 at MWCC.

Gongylonema pulchrum

Esophageal worm of ruminants

• Found: Worldwide​

• Affects: Sheep, goats, cattle (more rarely pigs and horses)​

• Adult worms live in esophagus, embeds in mucosal lining​

• Ingestion of intermediate host is the dung beetle or cockroach​

• "Worms with bumps" - zigzag shape​

• Eggs seen on fecal flotation

Trichostrongylus sp, Haemonchus sp.

"Hair round" (Trichostrongylus), "Blood spear" (Haemonchus)

• Often most common nematode in ruminants

• Cattle, sheep, goats​

• Adults found in abomasum, sm. & lg. intestine​

• Cause of infection: Ingestion of infective larvae​

• Trichostrongylus is zoonotic, Haemonchus is not​

• Eggs are morulated and too similar to differentiate genus in a fecal​

• Feed on blood of host​

• Treated with fenfendazole, levamisole and ivermectin

Bottle jaw in sheep

Infection with Haemonchus may overwhelm a host's ability to replace proteins and blood lost. This results in decreased intravascular oncotic pressure resulting in edema. The gathering of edema in the submandibular area is termed 'bottle jaw'.

Strongyloides papillosus

Threadworm

• Found: Worldwide​

• Cause of infection: Ingestion of larvae or penetration of skin (between hooves); migrate to lungs, coughed up and swallowed​

• Parthenogenetic larvae have a rhabitiform esophagus​

• Stage 3 larvae can be free-living or infective​

• Can pass in colostrum​

• Prepatent period: 5-7 days​

• Constant reinfection from pasture living - can reduce reinfection by rotation pasture with nonruminant animals (horses, mules, donkeys)

Trichuris ovis

Whipworms - "Hair tail"

• Found: Worldwide​

• Cause of infection: Ingestion of infective ova​

• Adults in cecum and colon​

• Unembryonated eggs with bipolar plugs

Elaeophora schneideri

Arterial sheep worm - "Bearing oil"

• Found: In Western and Southwestern United States​

• Only domestic host is sheep​

• Carried by infected horse flies​

• Adults in common carotid, can cause obstructions​

• Microfilariae only found in skin capillaries in face, can cause dermatitis​

• Prepatent period: 4.5 months or longer

Dictyocaulus sp.

Ruminant lungworm - "Netlike stalk"

• Found: Worldwide​

• Cause of infection: Ingestion of infective larvae​

• Adults live in bronchi, females lay eggs in lungs, coughed up, swallowed and hatch in intestine, larvae mature in environment to infective stage​

• Ingested larvae migrate to lymphatics, then to the heart, then to the lungs where they mature ​

• Coughing is most common symptom​

• Eggs can be found in sputum​

• Larvae can be found in fecals

Stephanofilaria stilesi

"Crown thread"

• Found: In United States

• Transmitted by the horn fly Haematobia irritans​

• Cause dermatitis along ventral midline, near umbilicus​

• Starts as small red papillae, then larger areas of pruritus and alopecia with a thick, moist crust​

• Adults and microfilariae can be found in skin scrapings​

• Must be careful not to confuse skin microfiliariae with Rhabditis strongyloides which is present in almost all domesticated animals and can also cause dermatitis

Thelazia sp.

• Transmitted by the intermediate host, the face fly (Musca autumnalis)​

• Adults found in conjunctiva and tear duct​

• Tears can have eggs or first stage larvae

Setaria cervi

• Carried by female mosquito​

• Adults are large and white and found at necropsy or during surgery free inside the peritoneal cavity​

• Microfilariae can be found in peripheral blood smears

Habronema sp. Draschia sp.

Horse stomach worm

• Found: Worldwide​

• Passed by flies (Muscidae family) which is intermediate host​

• Symptoms: Gastritis, diarrhea, nodules in stomach​; can also cause skin involvement "summer sores"​

• Elongated, thin shelled, larvated eggs found in fecals​

• Eggs or larvae ingested by flies​

• Cause of infection: Horse accidentally ingests fly with infective larvae inside​

• Fly control and pasture rotation can limit infections

Trichostrongylus axei

• Feed on blood in horse stomach​

• Ingestion of infected soil​

• Can also infect cattle, sheep and pig​

• Strongyle egg found in fecal float​

• Pasture management, treatment and pickup of feces can limit infections

Parascaris equorum

• Found: Worldwide​

• Small intestine of horse, mainly foals​

• Cause of infection: Ingestion of ova​

• Larvae migrate to liver through hepatic portal vein, then travel to lungs, coughed up and swallowed​

• Largest of equine nematodes, can grow to 50cm​

• Adults have distinctive lips​

• Light infections can be asymptomatic, heavy infections can cause unthriftiness, colic, potbelly, depression and cough

Strongylus vulgaris, Strongylus equinus

• Found: Worldwide​

• Cause of infection: Ingestion of larvae​

• Adults live in large intestine​

• Large strongyles — most pathogenic

• Strongyle egg​

• Eggs pass into environment and develop into larvae on blades of grass​

• Larvae migrate through mesenteric arteries to the liver, molt into next stage, migrate back to large intestine and mature in mucosal lining​

• Symptoms: Colic, weight loss, fever, lethargy, loss of appetite

Oxyuris equi

Horse pinworm

• Found: Worldwide​

• Adults in cecum, colon, rectum​

• Adult females exit anus, lay eggs with sticky, irritating gel that causes pruritus​

• Horses will swish tails constantly, rub their rumps and have broken tails hairs​

• Prepatent period: 4-5 months​

• Eggs can rub off on fencing or feeders and infect same host or new animals​

• Eggs have single operculum with flat end, often larvated​

• Eggs can be found on fecal scraping or scotch tape test​; rare to find eggs on fecal flotation

Habronema sp., Draschia sp

Stomach worm

• Adults are only found in the stomach, but larvae are deposited by house flies (Musca domestica) onto the skin and can cause cutaneous habronemiasis or "summer sores"​

• Often go away over the winter untreated​

• Most often found on legs, withers and male genitals

Onchocerca cervicalis

"Tumor tail"

• Carried by the intermediate host, the biting midge​ ("No see-ums"​)

• Adults are in ligamentum nuchae​

• Microfilariae are in dermis​

• Symptoms: Itching, alopecia, patchiness along head, neck and ventral midline​

• Microfilariae in skin scraping is not diagnostic as 90% of animals are infected​

• Diagnostic is by punch biopsy placed in saline on slide- can see vigorously swimming microfilariae​

• In rare cases, can cause opthalmia and blindness

Ascaris suum

• Found: Worldwide​

• Cause of infection: Ingestion of infective ova​

• Not zoonotic​

• 5mm wide and 41 cm long​

• Adults can be passed in feces, can cause bowel obstruction​

• Eggs passed in feces and hatch in environment as infective larvae​

• Larvae hatch and migrate to liver, molt, migrate through blood to lungs, coughed up and swallowed.​

• Adults mature in small intestine​

• Symptoms: Reduced weight, unthriftiness, respiratory symptoms in pigs

Oesophagostomum dentatum

"Esophagus mouth"

• Found: Worldwide

• Nodular worm of pigs​

• Large intestine​

• Larval form causes nodules to form in the large intestine, can cause obstruction​

• Prepatent period: 50 days​

• Strongyle type egg​

• Symptoms: Anorexia, diarrhea,​ weight loss

Trichinella spiralis

"Small hair"

• Pigs are intermediate AND definitive host​

• Adults in small intestine​

• Found: Worldwide (except for Australia and Denmark)​

• Cause of infection: Ingestion of contaminated, undercooked pork​

• Zoonotic​

• Female 4mm long, male is smaller​

• Larvated egg​

• Domestic animals often asymptomatic​

• Larvae encyst in skeletal muscle​

• Diagnosed by muscle biopsy

Metastrongylus elongates

• Found: Worldwide​

• Earthworm is intermediate host​

• Cause of infection: Ingestion of earthworm ​

• Adults in bronchi and bronchioles​

• Prepatent period: 24 days​

• Heavy eggs, must be flotation solution with SG >1.25 or by sedimentation​

• Symptoms: Cough, slow growth, unthriftiness