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25 Cards in this Set

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Classes of Platyhelminthes

Turbellarians - free-living carnivores

Cestodes - tapeworms

Trematodes - flukes

Orders of Trematodes

Monogenia - ectoparasites of aquatic animals

Digenea - tissue- or blood-dwelling endoparasites


Order of Trematodes

- ectoparasites of aquatic animals

- hermaphrodites

- direct life cycle

- viviparous

- feed on epidermis, blood, mucus

- Gyrodactylus spp and Dactylogyrus spp

Gyrodactylus spp

- Trematoda Monogenia

- Ectoparasites on skin and gills of aquatic animals

- Haptor for attachment

- Treated with praziquantel, but hard to get rid of


- Order of Trematodes

- Most are hermaphrodites

- Oral and ventral suckers

- Intermediate hosts w/ indirect development

- Alternate b/w sexual (in definitive host) and asexual (in the intermediate) reproduction

- Snail is intermediate host for all these hosts

Digenea Life Cycle

- Eggs in water hatch into miracidium

- Infect snails --> develop into sporocysts then redia or daughter sporocysts --> asexual reproduction --> release cercaria

- Cercaria swim around and form metacercaria in vegetation or second intermediate host then ingested by definitive host OR directly penetrate

- Reproduce sexually --> eggs

How Digenea Enter Definitive Hosts

- Eat metacercariae encysted on vegetation

- Eat infected secondary host

--- aquatic animals, arthropods, amphibia

- Direct penetration of skin by larval cercaria

Fasciola hepatica

- Platyhelminthes Trematoda Digenea

- Liver fluke that encysts on vegetation

- Large, operculate, unembryonated eggs in feces

- Diagnostic stage = eggs in feces

- Definitive Host = sheep, cattle, humans (zoonotic)

Fasciola hepatica Life Cycle

- Unembryonated egg in feces of sheep, cattle, human

- Develops into miracidium, infects snail

- Develops into sporocyst then redia in snail, asexual reproduction to cercaria and released

- Cercaria encyst on vegetation as metacercaria

- Ingested, encyst in duodenum, penetrates intestinal wall then in abdominal cavity and penetrates liver. (3-4 months overall)

Pathogenesis of Fasciola hepatica Acute Disease

- Due to ingestion of large #s of metacercaria

- Juveniles tunneling in liver result in thrombi and coagulative necrosis

- Secondary Clostridium novyi in these liver lesions leading to necrosis, hemorrhage, death

- Adults reside in bile duct and feed on blood, cause bile duct hyperplasia, anemia

Pathogenesis of Fasciola hepatica Chronic Disease

- F. hepatica lives in bile duct, causes hyperplasia, fibrosis, and calcification

- See hyperproteinemia, anemia, wasting disease

- Weight loss! Bottle jow, ascites, emaciation

Fasciola hepatica Treatment

- Treat adults (when environment is not conducive to egg survival: hot/dry or cold)

- Albendazole, triclabendazole, clorsulon

- Mulluscicide

- Move to fluke-free pastures

Fascioloides magna

- Platyhelminthes Trematoda Digenea

- Definitive host: deer

- Form cysts in liver that connect to bile duct

- Can infect sheep/goats and do not mature, so juveniles stay in liver

- No eggs in the aberrant hosts, so no eggs to diagnose


- Typical trematode lifecycle, encyst on vegetation

- Patent in sheep, cattle, deer

- Adults harmless. Pear-shaped with oral, ventral suckers

- High infective dose - get disease due to parasites migrating from small intestine to rumen

- Eggs often confused with Fasciola hepatica

Nanophyetus salmincola

- Platyhelminthes Trematoda Digenea

- Intestinal fluke

- Metacercaria on salmonids (fish eaten by definitive host)

- Diagnose by eggs in stool

- These flukes carry Neorickestsia helminthoeca which is pathogenic for salmon

Paragonimus kellicotti

- Platyhelminthes Trematoda Digenea

- Lung fluke, found as pairs

- Cause respiratory disease from migration in lungs

- Metacercaria in crustateans (fish eaten by definitive host - often dogs)

- Eggs are coughed out of lungs - either in mucus or swallowed and released in feces

- Eggs is operculate with collar-like structure

Platynosomum fastosum

- Platyhelminthes Trematoda Digenea

- Liver fluke of cats in SW US and West Indies

- Metacercariae in amphibians, lizards, geckos

Alaria spp.

- Platyhelminthes Trematoda Digenea

- Many definitive hosts - often wildlife

- Vertical transmission via milk

- Cercaria infect tadpoles, form Mesocercaria

- Eaten by definitive host or paratenic host

- Mesocercaria in lungs of definitive host form metacercaria, coughed, swallowed, mature to adults in gut

- IF lactating, metacercaria instead formed in mammary glands.

Dicrocoelium dentriticum

- Platyhelminthes Trematoda Digenea

- Definitive host: sheep, cattle, pigs - bile duct

- Terrestrial life cycle. Slimeball released by snail with cercaria, ant attracted to it - form metacercaria in ants. They climb up to top of grass to be eaten by sheep

- Small worms, operculate eggs, lancet-shaped

- Clinical disease: bile duct fibrosis & cirrhosis

Schistosoma japonicum

- Platyhelminthes Trematoda Digenea

- Definitive host: humans - zoonotic, water buffalo

- Percutaneous route of infection

- Two sexes.

- Live in vasculature near liver, migrate to gut, expelled in feces, infect snail, cercariae = infective

- Eggs cause chronic disease by lodging in tissues and forming granulomas

Heterobilharzia americana

- Platyhelminthes Trematoda Digenea

- Definitive host: dogs, raccoons, rabbits

- Percutaneous route of infection

- Predilection site: mesenteric veins.

- Usually asymptomatic, but eggs evoke granulomatous response

Swimmer's Itch

Avian schistosome infection (Digenea trematode with percutaneous route of infection)

- The cercariae die after skin penetration

- Delayed-type hypersensitivity reaction


- Thorny head worms

- Separate sexes

- No gut

- High reproductive output

- Male cement glands to seal female vagina after copulation

Acanthocephalans Life Cycle

- Sexual reproduction in vertebrate host, make eggs, released in feces.

- Egg ingested by invertebrate.

- Larval form in egg (Acanthor) hatches and forms Acanthella.

- Acanthella migrates and forms a cystacanth

- Ingested by vertebrate.

- Cystacanth encysts and gives rise to adults.

Macracanthorhynchus hirudinaceus

- Acanthocephalan

- Small intestine of pigs, sometimes dogs

- Intermediate host = beetles

- Not generally important in N. America (pigs raised on concrete). Treat w/ ivermectin.

- Highly pathogenic. Necrosis at local site, ulceration and granulomas, competition for nutrients leads to wasting.

- Eggs in feces diagnostic. Thick, brown shell.