Platyhelminths (Exam 3)

Exam 3 of Parasitology is the Platyhelminths. Blue text is testable material, black text is general info or potential extra credit

The scientific and common name for these parasites

Platyhelminths AKA Flatworms

Trematodes are also known as

Flukes

Platyhelminths > Trematodes

Cestodes are also known as

Tapeworms

Platyhelminths > Cestodes

Platyhelminths: Morphologic features

No body cavity (Acoelomate)

Typically hermaphroditic

Muscular suckers

Cestodes lack what?

Digestive tract is absent

This is an example of an adult and egg of a ___

Platyhelminths > Trematodes

The adult sexual stages of Trematodes are found in what parts of the body of the hosts?

Adult sexual stages found in intestines, bile ducts, lungs, blood vessels of vertebrate final hosts → eggs passed in feces

Asexual stages of Trematodes are found in what?

Often found in mollusks (such as snails)

True or False: It is common for Trematodes to have second intermediate or paratenic hosts

True!

Describe a Typical Trematode Lifecycle

1. Adults in host (intestines, bile ducts, lungs, blood vessels) pass eggs into feces

2. Eggs fall into water and develop to Miracidium (a free-swimming ciliated larvae)

3. Miracidium hatches through operculum

4. Miracidium enters snail intermediate host, and forms a sporocyst

5. Sporocyst develops rediae (another larval stage)

6. Cercariae (a free swimming larvae) develop in rediae and exit snail

7. Cercariae swim to vegetation and encyst as metacercariae (dormant) or infect a second intermediate host

8. Metacercariae ingested by definitive host. Fluke travels to its location in host

What is the infective stage of a Trematode life cycle?

Metacercariae

Name this Trematode

Platyhelminths > Trematodes > Fasciolidae

Leaf-like body, dendritic ovaries and testes

(Trematodes from ingesting vegetation group)

Where do Fasciola trematodes live in their hosts?

Reside in liver and bile ducts of mammals and humans

How is Fasciola acquired?

Acquired through ingestion of metacercariae on plants

Metacercariae survive in environment for months

Fasiola hepatica: Where in world?

Gulf Coast, Pacific Northwest

Fasciola gigantica: Where in world?

Hawaii, tropical and subtropical regions

Fasciola hepatica: Common name, Hosts

Platyhelminths > Trematodes > Fasciolidae > Fasciola hepatica

Common Liver Fluke

Most commonly in cattle, sheep and goats, can infect humans

(Trematodes from ingesting vegetation group)

Fasciola hepatica: Is often fatal in what species?

Often fatal in sheep and camelids

Rarely fatal in cattle

Life cycle of Fasciola hepatica once ingested

Ingested metacercariae excyst in the duodenum of host, penetrate intestinal wall, migrate to liver to bile ducts. Migration lasts 6-8 weeks

Name this Trematode: Common and scientific

Platyhelminths > Trematodes > Fasciolidae > Fascioloides magna

Giant Liver Fluke

(Trematodes from ingesting vegetation group)

Fascioloides magna is larger or smaller than Fasciola? Another morphologic difference?

Fascioloides magna is larger than Fasciola.

Fascioloides magna also lack an anterior cone projection

Fascioloides: Where in world? Definitive host? Other hosts?

Worlwide distribution, more common in Northeast than Fasciola hepatica

White tailed deer definitive host

Nonpatent infections in cattle, sheep, goats, llamas and alpacas

Does Fascioloides pass eggs in feces of its definitive host? In other hosts?

Yes eggs passed in deer. No not in other hosts (cattle, sheep. goats, llamas, alpacas)

Fascioloides magna causes severe damage when?

When migrating through the liver

Fasciolidae (Fasciola and Fascioloides): Disease

Can cause similar disease

Fascioloides more pathogenic than Fasciola, especially in small ruminants

Fascioloides can be walled off in cattle, but continuously migrates in sheep and goats

Aberrant migration to diaphragm and vena cava reported

Potential transplacental spread reported

Acute fluke disease

Invasion of liver by young flukes cause significant damage to liver → rapid death

Black Disease: Common name, caused by

Infectious necrotic hepatitis

Fluke damage to liver (necrotic anaerobic area) reactivates dormant Clostridium novyi bacterium spores, causing release of clostridial toxins → causes fatal toxemia

Fasciolidae: Diagnosis

Eggs passed in feces detected on sedimentation ONLY in patent hosts (White-tailed deer)

Premortem diagnosis of fascioliasis difficult in aberrant hosts

Prepatent period 60 days for Fasciola hepatica

Prepatent period 270 days for Fascioloides magna

Fasciolidae hepatica, Fascioloides magna: Treatment

Fasciolidae hepatica: Clorsulon + ivermectin, albendazole. Resistance demonstrated

Fascioloides magna: Much harder to kill juvenile flukes, can try albendazole, off-label clorsulon, triclabendazole, closantel

Prevent infection with proper snail and deer control

Name this Trematode: Scientific and Common names

Platyhelminths > Trematodes > Paramphistomum cervi

Rumen flukes

(Trematodes from ingesting vegetation group)

Paramphistomum cervi: Where live in what hosts?

Live in rumen of cattle, sheep and goats

Paramphistomum cervi: Morphologic feature

Adults have a ventral sucker at posterior end of body (acetabulum)

Paramphistomum cervi: Life Cycle (brief)

Eggs passed in feces, miracidia hatch and invade snail, cercariae encyst as metacercariae on aquatic vegetation, ingested by host

Paramphistomum cervi: Fluke migration path in host, migration causes?

Ingested metacercariae excyst in small intestine, migrate through small intestine back to rumen

Migration of immature flukes can rarely cause prolonged etneric disease

Diarrhea, depression, anorexia

Young cattle more affected

Sheep and goats of any age can be affected

True or false: Adult Paramphistomum cervi flukes are pathogenic

False. The adult flukes are nonpathogenic.

Paramphistomum cervi: Treatment

No labeled treatments in US

Clorsulon: MOA, effective against

Works by blocking glycolytic enzymes, impairing energy production

Effective against immature and mature Fasciola hepatica

Available in a combination with ivermectin (for nematodes and arthropods)

Given as SQ injection

Practice Question: Which of the following trematode life stages is infective on ingestion by the final host?

Answer = Metacercaria

Practice Question: What is the name of the structure indicated by the arrow?

Answer = Operculum

Practice Question: Which of the following bacteria is involved in the pathogenesis of Black Disease in ruminants?

Answer = Clostridium novyi

Practice Question: Which is the most appropriate method to control Fascioloides magna infection in sheep and goats?

Answer = Fencing off ponds and marshy areas (Snail control)

Practice Question: Which of the following is true regarding paramphistomes?

Answer= There are no approved treatments for this parasite. (cattle sheep and goats NOT horses, migration of immature flukes cause disease not adults)