Platyhelminthes - Details Flashcards
Phylum Platyhelminthes
General Characteristics
-Flatworms
-Most are parasitic.
-Almost all are flattened in shape.
-Usually leaf-shaped or oval.
*except: tapeworms, very long and thin.
-Range in size from:
Almost microscopic to over 200 cm long.
-Many are hermaphroditic.
Phylum Platyhelminthes
–Class Cestoda
General Characteristics
- ALL are parasitic.
- Genera of Vet Importance:
- Taenia, Diphyllobothium, Echinococcus, Spirometra.
- Almost always require an intermediate host.
- Adults are parasites of intestines of vertebrates.
- Larvae are parasites of various vertebrates or invertebrates.
- Many important parasites of domestic animals.
- Live in intestines & are only seen when passed w/feces.
- Hermaphroditic & self-fertilizing
- Infects almost any mammal.
Phylum Platyhelminthes
–Class Cestoda
General Life Cycle
-Require definitive host (DH) & 1 or 2 intermediate hosts (IH).
*intermediate may be:
vertebrate: mice, rabbit, etc.
Invertebrates: crustaceans, insects, molluscs, mites, annelids…
-Cestodes of great vet importance have 1 intermediate host:
*mammal: Taenia spp.
*arthropod: Dipylidium spp.
-Life cycles vary widely, many are not well known.
-Sexually mature tapeworms live in intestine of definitive host.
*mature adults may live a few days to many yrs (depends on species).
*mature adults may produce a few to millions of eggs.
-Eggs excreted in feces.
-Each proglottid has 1 or 2 complete sets of male & female repro organs.
*female: ovary & associated structures.
*male: testes & associated structures.
Phylum Platyhelminthes
–Class Cestoda
General Steps
- Hermaphroditic self fertilization produces eggs in a proglottid.
- Eggs and/or proglottid excreted in host feces.
- Eggs ingested by intermediate host, hatch.
- Hatched egg invades a paraenteral (extraintestinal) site in IH.
- Larvae in paraenteral site of IH develop into metacestode (juvenile) or cysticercus.
- IH is ingested by DH.
- In DH, larvae go to small intestine.
- In intestine, most of body of larva is digested, leaves neck & scolex.
- Scolex attaches to inside of host intestine.
- Neck begins to bud off segments that become proglottids.
- Matures into adult in DH intestines (enteral site)
Phylum Platyhelminthes
–Class Cestoda
General Disease
- Adult cestodes in intestines of dogs & cats rarely cause serious disease.
- may be unthriftiness, malaise, irritability, colic, mild diarrhea.
- pruritus ani (irritated rectum) is common in dogs.
- Severe Cases: emaciation & seizure.
Phylum Platyhelminthes
–Class Cestoda
General Diagnosis
- Finding proglottis or eggs in feces (direct smear or flotation).
- May not be able to distinguish eggs of various genera by microscope.
- May be confused w/hookworm eggs.
Phylum Platyhelminthes
–Class Cestoda
General Anatomy
They all have a scolex, neck, & strobila.
Phylum Platyhelminthes
–Class Cestoda
General Anatomy Strobila
Strobila
- Unique structure which makes up body of animal.
- Consists of linear series of sets of repro organs of both sexes.
- Each section is called a proglottid or proglottis.
- One tapeworm may contain 2,000 proglottids.
- Very flat, absorb nutrients through skin.
- Each proglottid is self fertilizing & produces eggs.
- each has male & female reproductive organs.
- New proglottids are produced at the anterior end of organism.
- Proglottids sexually repro & produce eggs as they travel towards posterior end.
- strobilation
- Gravid: proglottid contains fully developed eggs.
- Gravid proglottid reaches end of strobilis & breaks off.
- pass out in feces.
Phylum Platyhelminthes
–Class Cestoda
General Anatomy Scolex
Scolex
- The head, at anterior end of organism.
- Equipped w/variety of holdfast organs, maintain position of parasite in host gut.
- May have suckers, grooves, hooks, spines, gland, tentacles, or any combo of these.
- Rostellum: structure at one end of scolex containing hooks or other attachment appendages.
- Hold onto & often penetrates the wall of host intestine.
Phylum Platyhelminthes
–Class Cestoda
General Anatomy Neck
Neck
-Area between Scolex and Strobilus.
Dipylidium caninum What animal(s) does it infect?
Dogs, Cats
Dipylidium caninum
General Characteristics
- Rare in cats.
- Very rare in humans (child).
Dipylidium caninum
Shed in Feces
Shed in Feces (and/or):
- Proglottids
- look like rice grains (cucumber seeds).
- move around in feces.
- Eggs
- shed in “egg packets”.
- each packet contains ~a dozen eggs.
Dipylidium caninum
Adults
Adults
- Scolex: has 4 suckers, rostellum w/ several rows of hooks.
- Up to 50 cm (20”), usually 6” or more.
- Feeding:
- absorb nutrients through skin.
- feeds on material passing through intestines.
- do NOT suck host’s blood
Dipylidium caninum
Life Cycle - Direct or Indirect
- Indirect
* IH: fleas (usually), lice
Dipylidium caninum
Predilection Site
Small Intestine
Dipylidium caninum
Prepatent Period
2 to 3 weeks
Dipylidium caninum
Life Cycle
- Perianal region of infected dog or cat becomes contaminated w/eggs from feces.
- Larval flea or louse (IH) ingests eggs.
- Cysticercus (metacestode) develop in IH & becomes infective.
* usually occurs in muscle of IH. - Dog or cat ingests IH while grooming.
- Cysticercus (metacestode) goes to intestine of DH.
- In intestine, matures & develops proglottids.
- Gravid proglottids containing eggs develop in ~2 weeks.
- Gravid proglottids and/or eggs are excreted in feces.
NOTE: Eggs are NOT infective to vertebrates, only to fleas & lice.
Dipylidium caninum
Symptoms & Disease
-Usually fairly asymptomatic in dog/cat.
-Dogs frequently sit down, drag bottoms.
*tapeworm proglottid (motile) on perianus itches.
~called pruritus ani (has many
Dipylidium caninum
Treatment
Treatment
- Usually easily treated & eliminated.
- Reinfection usually occurs.
- infected flea pop in house/enviro.
- flea control Is necessary to prevent this.
Taenia pisiformis What animal(s) does it infect?
Dogs, Foxes, other canids.
Taenia pisiformis
Shed in Feces
Shed in Feces:
- Proglottids
- Eggs
- NOT in packets.
- single eggs seen in feces.
- thick striated shells.
Taenia pisiformis
Adults
Adults
-Scolex: has 4 suckers, rostellum w/2 rows of hooks.
Taenia pisiformis
Life Cycle - Direct or Indirect
- Indirect
* IH: rabbits, hares
Taenia pisiformis
Predilection Site
Small Intestine
Taenia pisiformis
Prepatent Period
1 to 2 months
Taenia pisiformis
Life Cycle
- Gravid proglottids containing eggs are passed in dog feces.
- Proglottids crawl around in feces onto surrounding vegetation.
- Eggs released from proglottids in envrio.
- Rabbit ingests eggs on vegetation or in feces.
- Egg hatches in sm intestine of rabbit & travels to liver via blood.
- Develops into cysticercus (metacestode) in rabbit.
- Cysticercus usually forms dormant cyst in rabbit.
- Dog eats rabbit
- The cysticercus (often encysted) attaches to sm intestine of dog & matures there.
- Mature tapeworm in dog intestine form gravid proglottids.
Taenia pisiformis
Symptoms & Disease
- Usually asymptomatic.
- Very heavy infections in sm dogs may cause intestinal blockage.
Taenia pisiformis
Diagnosis
- Proglottids or eggs in feces.
- Proglottids are much larger & more rectangular than those of D. caninum.
Taenia taeniaeformis What animal(s) does it infect?
Cats.
Taenia taeniaeformis
Life Cycle - Direct or Indirect
- Indirect
* IH: rodents
Class Digenea
General Characteristics
Digenea
- Undergo indirect development.
- what hatches from egg is distinctly different in body form from adult.
- development w/metamorphosis.
- Sexual & asexual generations parasitize alternate hosts.
- Development occurs in at least 2 hosts.
- First host usually a mollusc or annelid.
- Second host can be almost any mammal.
Class Digenea
Anatomy
Anatomy (adult form)
- Size ranges from .16 mm to 5.7 cm.
- Most are flattened & oval shaped.
- Have a powerful oral sucker that surrounds the mouth.
- Strong muscular pharynx just below oral sucker.
- Most are hermaphroditic.
- many are self-fertilizing.
Fasciola hepatica What animal(s) does it infect?
Ruminants (mostly)
Fasciola hepatica
General Characteristics
Adults
- Matures in bile duct of host.
- Leaf shaped.
- Hermaphroditic.
- Adult body is basically a little bag of male & female repro organs
- Have an oral sucker surrounding mouth & a ventral sucker.
Fasciola hepatica
Common Pathogens
Common Pathogens
- Fasciola hepatica
- Fasciola gigantica
- Fasciola magna
Fasciola hepatica
Life Cycle - Direct or Indirect
- Indirect
* IH: snail
Fasciola hepatica
Predilection Site
Bile Duct
Fasciola hepatica
Prepatent Period
8 to 10 weeks
Fasciola hepatica
Life Cycle
- Adult live in bile ducts of mammalian host.
- Eggs produced by adult go through intestines & are excreted in feces.
- In the enviro, egg hatches to release a ciliated miracidium.
*juvenile form.
*2 to 4 weeks after excretion. - Miracidium penetrates the first IH.
*if it doesn’t find an IH in 24 hours, it dies. - In the snail, the miracidium discards its ciliated “skin” & metamorphoses into a simple form called a sporocyst.
- In the sporocyst, a number of embryos develop to form redia.
*redia grow & burst the sporocyst.
*are liberated in snail tissue.
*have mouths & digestive glands & eat their way through snail tissue. - Redia develop into cercaria.
*1 to 2 months.
*has a tail to aid in swimming. - Cercaria leaves the snail & enters surrounding water.
- Cercaria attaches to aquatic plant, looses tail, and encysts.
*metamorphoses into a metacercaria.
*metacercaria are infective to mammals.
~esp ruminants, can also infect humans.
*highly resistant, may survive on hay for a long time. - Grazing mammal ingests plants containing metacercaria.
- Metacercaria is digested in mammalian host’s sm intestine.
- Forms a young, which invades host’s liver.
- In several weeks, young flukes migrate to host bile ducts.
- Mature into adult flukes in bile ducts.
- Complete life cycle takes 3 or 4 months (summer).
- Transmission peaks between Feb & Nov & varies w/parts of the country.
Fasciola hepatica
Acute Fluke Disease
Acute Fluke Disease
- Occurs during invasion of the liver by recently ingested metacercaria.
- Maritas invade liver & cause sever liver inflammation.
- Abdominal pain & disinclination to move.
- Highly fatal.
- some may display no symptoms prior to death.
- death usually due to blood loss from hemorrhaged liver.
Fasciola hepatica
Chronic Fluke Disease
Chronic Fluke Disease
- Much more common than acute.
- Adult flukes in bile ducts.
- Overall weakness, weight loss, anemia, chronic diarrhea.
- Swelling in abdomen.
- Obstructed bile duct, destruction of liver tissue, hepatic scarring.
- Can be fatal.
Fasciola hepatica
Diagnosis
- Finding adult flukes in bile ducts or liver on necropsy or eggs in feces on necropsy.
- Sucrose fecal floats distorts eggs, but they can still be recognized.
- Sedimentation techniques are preferred.
- Eggs are oval w/visible operculum (lid).
The presence of one fluke leads to condemnation of liver in slaughter houses.
*fairly common
Paragonimus kellicotti What animal(s) does it infect?
Dogs, Cats, Other domestic & wild animals. Humans.
Paragonimus kellicotti
Shed in Feces
- Eggs
- oval, golden brown.
- coughed up & swallowed.
Paragonimus kellicotti
Adults
Adults
- Oval, reddish brown
- About 14 x 7 mm (about 1/2”)
- Visible operculum (lid).
Paragonimus kellicotti
Life Cycle - Direct or Indirect?
- Indirect
- IH1: snail
- IH2: crayfish or crabs
Paragonimus kellicotti
Life Cycle
- Eggs shed in feces of infected animal.
- Eggs hatch in water & miracidium emerges.
- Miracidium infects snail.
- Develops into cercaria in the snail.
- Cercaria leaves snail & infects a crayfish.
- Develops into metacercaria in the crayfish.
- Dogs & cats become infected when they eat infected crayfish.
- Young flukes pass through intestinal wall & invade lungs.
- Mature & produce eggs in lungs (in cysts).
- Eggs are coughed up & swallowed, excreted in feces.
Paragonimus kellicotti
Symptoms & Disease
- Chronic, deep, intermittent cough.
- Weak, lethargic.
- May be asymptomatic.
Paragonimus kellicotti
Diagnosis
- Eggs in feces or sputum.
- Eggs hard to prepare for ID.
- sedimentation much better than floatation.
- if use flotation, must use high density sucrose.
- Operculum in egg helps to id the egg.
