Veterinary Parasitology CH8 - Trematodes of Domesticated Animals

Study material for Chapter 8 of Diagnostic Parasitology for Veterinary Technicians. For class BIO225 at MWCC.

Dicrocoelium dendriticum

“Forked bowl” or “Lancet fluke”

• Affects: Sheep, goats, cattl

• Adults live in bile duct​

• 1st intermediate host: Cionella lubrica land snail — Unique in that intermediate hosts are not aquatic​

• 2nd intermediate host: Formica fusca, ant– behavior of both snail and ant can be altered by infection—ant brain infection leads to tetanus of jaw muscles so they stick to the grass​

• Found: Worldwide

• Zoonotic​

• Operculated egg, adult is only 1-2.5 mm across and 6 to 10 mm long​

• Oral sucker, ventral sucker, two testes and lateral vitellaria that secrete yolk and help provide nutrition and shell for the egg

• Can cause hyperplasia of bile duct leading to obstruction

Paramphistomum sp. and Cotylophoron sp.

“Rumen fluke”

• 1st intermediate host: aquatic snail​

• No 2nd intermediate host: metacercariae bind to vegetation​

• Cause of infection: Ruminants eat vegetation

• “Amphistome” means 2 mouths. Obvious oral sucker on one end and ventral sucker is at opposite end.​

• Adults are not pathogenic, but migration of young flukes can cause problems as they eat the intestinal lining​

• Not zoonotic

Fasciola hepatica

“Liver fluke”

• Affects: Sheep, cattle, goats

• Causes “liver rot”​

• 1st intermediate host: Aquatic snail​

• No 2nd intermediate host​

• Cause of infection: Ingestion of vegetation with metacercariae​

• Most economically important, most studied fluke​

• Adults obstruct bile duct 30 x 13 mm, broad anterior end with cone shape projection, more narrow posterior end​

• Tan to reddish brown​

• Eggs found in fecal sedimentation

Fasciola magna

• Affects: White tailed deer, can use ruminants and sheep as incidental host​

• 1st intermediate host: aquatic snail​

• No 2nd intermediate host​

• Cause of infection: Ingestion of vegetation with metacercariae​

• Adults in liver parenchyma​

• Not zoonotic​

• Larger than F. hepatica at 10 cm long, and thicker at 4.5mm ​

• Eggs can be found in fecal sedimentation, but only in deer host​

Why do they call the cow or sheep the “dead end host” for Fasciola magna?

Incidental hosts will not release cysts in feces, only found at necropsy — “Dead end host” cannot transmit

Platynosomum fastosum

“Lizard poisoning fluke”

• Affects: Cats​

• Adult in bile ducts​

• Found: In S. America, Southern U.S. Carribbean, Pacific Islands​

• 1st intermediate host: land snail ​

• 2nd intermediate host: lizard​

• Cause of infection: Ingestion of infected lizards​

• Not zoonotic​

• Diarrhea, vomiting, jaundice​

• Tiny, only 4 to 8 mm long​

• Eggs can be found in fecal flotation

NanoIyphyetus salmincola

“Salmon poisoning fluke”​

• Affects: Dogs

• 1st intermediate host: freshwater snail​

• 2nd intermediate host: salmon​

• Found: In the Pacific Northwest of N. America​

• Zoonotic​

• Adult in small intestine, vector for Rickettsia bacteria causing Elokomin fluke fever​

• Smallest fluke at only 1.1mm in length, white or cream in color

Alaria sp.

• Affects: Dogs and cats​

• Found: In Northern U.S. and Canada​

• 1st intermediate host​

• 2nd intermediate host: frog, snake, mouse​

• Adult in Small intestine​

• Not zoonotic​

• Unique in that front is flat, but posterior half is thick and spherical​

• Adults are not pathogenic but migrating larvae can be

Paragonimus kellicotti

“Lung fluke”

• Affects: Dogs and cats​

• Adult found in lung​

• 1st intermediate host: operculated snail​

• 2nd intermediate host: crayfish​

• Cause of infection: Ingestion of crayfish​

• Zoonotic​

• Eggs found in sputum or fecal sedimentation​

• Adults are thick, brownish red, 16 mm x 8mm, can be seen on X-Ray

Heterobilharzia americana

“Canine blood fluke”

• Found: In N. America, particularly Gulf States (LA, MS)​

• Zoonotic, but rare​

• Cause of infection: Metacercariae enter through skin of dog​

• Adult found in mesenteric veins of intestine and portal veins of liver​

• Schistosomes “split body” NOT hermaphroditic, male and female of species​

• Long, thin flukes that can obstruct small veins​

• Symptoms: Bloody diarrhea, emaciation, anorexia​

• Egg containing miracidium can be found in fecal sedimentation

Human Blood Flukes

Blood flukes of Schistosoma (Bilharzia) genus can infect human​

• Found: In Africa, Middle East and Caribbean​

• Typically species specific so even if cattle or other domestic animals are infected, it is not common to see same species in humans​

• Cause of infection: Through the skin of humans who come into contact with water containing cercariae

What is Swimmer’s Itch? How is it caused?

Avian blood flukes are also common and can infect snails and then release cercariae that infect humans who swim in water where aquatic birds are migrating, causing Swimmer’s Itch.

What is Black Spot? How can birds get infected with it?

Avian blood flukes that release eggs into the water can infect snails and then release cercariae that infect fish. Metacercariae encyst in muscle and skin and fish increases melanin around them causing Black Spot. Cooked fish with Black Spot should not be able to infect humans, but birds can get infected by eating fish.