Platyhelminths (Exam 3)

Exam 3 of Parasitology is the Platyhelminths. Blue text is testable material, black text is general info or potential extra credit. General note: Dr. Wu uses the class name Secernentea, but Modern genetic studies use name Chromadorea (Secernentea is deeply nested within Chromadorea, making them closely related in taxonomy. Secernentea is not considered a separate, co-equal class; it is now typically reclassified as the order Rhabditida under the class Chromadorea)

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)

Name this Trematode

Platyhelminths > Trematodes > Nanophyetus salmincola

(Trematodes from ingesting hosts and skin penetration group)

Nanophyetus salmincola: Where live in host? Host?

Live as adults in small intestine of definitive host

Definitive hosts include dog, cat, coyote, fox, bear, raccoon, mink

Nanophyetus salmincola: Life Cycle

Eggs passed in feces from host, miracidia enter snail, cercariae penetrate salmonid skin, encysts as metacercariae, host ingests the salmon fish to become infected

Nanophyetus salmincola: Disease in host, What Disease can they cause?

Typically fluke infection itself causes no clinical signs

Enteritis can occur with large numbers

Flukes can cause a bacterial disease called salmon poisoning disease

Nanophyetus salmincola: Diagnosis and Treatment

Diagnosis: Eggs on fecal flotation

Treatment: Praziquantel

Pictured is hemorrhagic enteritis from what disease? What bacterial agent causes this disease and carried by what fluke?

Nanophyetus salmincola flukes contain the rickettsial agent Neorickettsia helminthoeca → Causes Salmon Poisoning disease in dogs

Common in West Coast of US

Salmon Poisoning Disease: Clinical Signs

Fever, anorexia, vomiting, diarrhea

Lymphadenomegaly of cervical and mesenteric lymph nodes

Hemorrhagic enteritis

→ Clinical signs resemble canine parvoviral infection

Salmon Poisoning Disease: Treatment

Doxycycline, oxytetracycline

What percentage of Salmon Poisoning Disease cases are fatal without treatment?

90%

Name this trematode: Definitive Host?

Platyhelminths > Trematodes > Paragonimus

(Trematodes from ingesting host/skin penetration group)

Cat and dog definitive host

Paragonimus kellicotti present in U.S. around Mississippi River basin

Zoonosis of Paragonimus westermani reported in Asia

Where do Paragonimus flukes live in host?

Live in pairs or groups in cysts within lungs of mammal definitive hosts (cats and dogs)

Paragonimus: What are the intermediate hosts?

Snail is the first intermediate host

The second hosts are crabs/crayfish

How is infection of Paragonimus flukes acquired?

Cats/Dogs acquire infection through ingestion of metacercariae in crabs and crayfish

Paragonimus: Disease

Immature flukes penetrate intestinal wall and migrate through diaphragm to lungs

Infection can be asymptomatic but can cause chronic coughing

Bullae can form and rupture leading to pneumothorax

Aberrant migration to viscera and brain reported

Paragonimus: Diagnosis (egg morphology)

Large, vase-shaped operculated eggs in feces or sputum. Have a thickened ridge surrounding operculum

Fecal sedimentation recommended because flotation less reliable

Transtracheal wash

Paragonimus: Treatment

Praziquantel, Fenbendazole, albendazole

Name this Trematode: Morphologic feature

Platyhelminths > Trematodes > Dicrocoelium dendriticum

(Trematodes from ingestion of host/skin penetration group)

Translucent bodies

Where do Dicrocoelium dendriticum flukes live and in what hosts?

Live as adults in gallbladder, bile and pancreatic ducts of mammals, birds and reptiles

Definitive Hosts: Sheep, cattle, pigs, llamas, alpacas, deer, woodchucks, rabbits

Dicrocoelium dendriticum: Life Cycle

Eggs from host ingested by land snail, cercariae leave snail in slime balls, ingested by ants and form metacercariae, (alters behavior of ants after flukes migrating to brain, ants travel to vegetation to be ingested by definitive host, burrow out of stomach and migrate to liver)

Dicrocoelium dendriticum: Disease, causes this seen in the picture

Large number of flukes usually with no clinical signs

Chronic disease can rarely cause progressive hepatic cirrhosis with cachexia, low wool production, decreased lactation

→economic losses from liver condemnation

acute decline and anemia can occur in new world camelids

Diagnosis this trematode infection passed on this egg morphology

Dicrocoelium dendriticum

Fecal flotation or sedimentation

Small lopsided yellow-brown operculated eggs

Dicrocoelium dendriticum: Treatment and prevention

Treatment: Albendazole, Praziquantel

Prevention relies on covering anthills or keeping insectivores to eat the ants (ducks, turkeys, chickens)

Name this Trematode

Platyhelminths > Trematodes > Platynosomum fastosum

(Trematode from ingesting host/skin penetration group)

Platynosomum fastosum infection is also known as?

Lizard poisoning disease

Platynosomum fastosum flukes live where and in what host?

Live as adults in bile and pancreatic ducts of cats

Where in the world are Platynosomum fastosum flukes live?

Common in southeastern US and Caribbean

Platynosomum fastosum: Life cycle

Eggs passed in feces

Develop to cercariae in land snails

Cercariae ingested by pill bugs and develop to metacercariae

Lizards, toads, skinks, geckos act as paratenic hosts after ingesting pill bugs

Cats infected by either ingesting pill bugs directly or the paratenic hosts

Platynosomum fastosum infections can cause this pictured? Disease clinical signs?

Most cats unaffected

Can cause acute and chronic cholangitis with fever, hepatomegaly, abdominal distension, jaundice, vomiting and diarrhea

Platynosomum fastosum infection/Lizard Poisoning disease is associated with development of what?

Associated with development of liver cancer such as cholangiocarcinoma

Platynosomum fastosum: Diagnosis and Treatment

Diagnosis: Eggs in feces on sedimentation

Treatment: Praziquantel, surgical removal

Name this Trematode: Where does it live and in what hosts?

Platyhelminths > Trematodes > Alaria

small flattened spoon-shaped flukes that live as adults in intestinal tract of canids and felids

Alaria: Life Cycle

Eggs passed in feces hatch in water

Infect Snail

Exit and penetrate tadpoles, develop to mesocercariae (unencysted metacercariae)

Mesocercariae can be passed to frogs, snakes or mice that eat the tadpoles

Definitive host (dogs, cats) ingest mesocercariae in intermediate host, develop to metacercariae in lungs, then coughed up and swallowed to mature to adult in intestine

Alaria: Disease

Usually no clinical signs from infection

Migration of mesocercariae can cause disease such as pulmonary hemorrhage

Adults can be associated with enteritis

Alaria: Diagnosis and Treatment

Diagnosis: Fecal sedimentation, flotation not as sensitive

Treatment: Praziquantel

How can Alaria be potentially zoonotic to humans?

If a human eats undercooked frog meat

Name this Trematode: Where does it live and in what host?

Platyhelminths > Trematodes > Schistosoma (Schistosomes)

Live as adults in mesenteric veins of birds and mammals

Schistosomes are unique in that there are what?

Separate sexes

Schistosomes mate where in the host?

The separate sexes of Schistosomes mate within mesenteric veins and pass eggs into bloodstream to then enter the intestine

Schistosomes eggs produce what and what does this cause?

Schistosomes eggs produce proteolytic enzymes that erode the mesenteric vein and intestinal walls → inducing granulomatous inflammation

Schistosomes: Life Cycle

Eggs hatch in water

Develop to cercariae in snail

Cercariae penetrate skin of definitive hosts

Migrate to Lungs, liver then mesenteric veins

Sexes mate within the veins, eggs pass into blood into intestine, passed in feces

Heterobilharzia americana is a species of _____ Trematode that can infect dogs where in the US?

Platyhelminths > Trematodes > Schistosoma > Heterobilharzia americana

Southern US

What animals can act as final hosts for Schistosomes?

Raccoons and dogs

How do final hosts acquire Schistosoma infections?

Cercareiae penetrate the skin of hosts while swimming

Schistosomiasis: Disease

Liver and intestinal lesions

Lethargy, weight loss, vomiting, diarrhea, hyporexia, anorexia, hypercalcemia, polyuria/polydipsia

Eggs can disseminate into body, causing widespread granulomas

Schistosomiasis: Diagnosis and Treatment

Diagnosis: Fecal sedimentation in NaCl → Eggs will hatch on exposure to water

Treatment: Fenbendazole, praziquantel, but treatment often unrewarding

Schistosomiasis can cause what in humans in the US? Patent or nonpatent infection?

Swimmer’s Itch → cercarial dermatitis is caused by waterfowl schistosomes

Caused by Cercariae invade human skin when swimming in ponds, which causes skin rash due to hypersensitivity reaction

Pruritus can last up to a week but eventually fades

(Schistosomiasis common in South America, Africa, and Eastern Asia. Can cause abdominal pain, diarrhea, anemia, and bloody stool)

Nonpatent infection in humans

Praziquantel: Effective against?

Isoquinolone anticestodal and antitrematodal drug, MOA uncertain.

Effective against a wide range of cestodes and trematodes

Oral and SQ injection

Related drug, espiprantel, also effective against cestodes and trematodes in dogs and cats

True or False: Praziquantel is not safe for use in breeding and pregnant animals because it crosses the blood-brain barrier.

False! It does cross the BBB but is still considered very safe for breeding and pregnant animals

Praziquantel: Side Effects

Can cause vomiting and tremors at high doses

Anorexia, diarrhea, salivation, sleepiness, and weakness reported

Resistance to Praziquantel developing in what cestode?

Dipylidium caninum

Other evidence of resistance in other cestodes and trematodes emerging

Practice Question: Which of the following is a clinical sign expected in a dog with salmon poisoning disease?

Answer = Swollen lymph nodes (cervical and mesenteric)

Practice Question: Identified on a transtracheal wash of a cat. How was this parasite acquired?

Answer = This is Paragonimus trematode, acquired through ingestion of crayfish (or crab) intermediate host

Practice Question: Which is true regarding Dicrocoelium dendriticum?

Answer = Large number of flukes can occur with no clinical signs

Practice Question: Which of the following is a clinicopathologic abnormality associated with schistosomiasis in dogs?

Answer = Hypercalcemia

Practice Question: Which of the following is a means by which final hosts can be infected with Alaria spp.?

Answer = Ingestion of mesocercariae in mother’s milk

Name this Class of Platyhelminths: Scientific and Common

Platyhelminths > Cestodes

AKA Tapeworms

Cestode adult morphologic features

Adults consist of a chain (Strobila) of individual reproductive segments (proglottids) attached by a holdfast (scolex)

Cestode egg morphology

Eggs are oncospheres = six-hooked embryo (hexacanth embryos)