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Phylum Platyhelminthes
General Characteristics

-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

1. Hermaphroditic self fertilization produces eggs in a proglottid.
2. Eggs and/or proglottid excreted in host feces.
3. Eggs ingested by intermediate host, hatch.
4. Hatched egg invades a paraenteral (extraintestinal) site in IH.
5. Larvae in paraenteral site of IH develop into metacestode (juvenile) or cysticercus.
6. IH is ingested by DH.
7. In DH, larvae go to small intestine.
8. In intestine, most of body of larva is digested, leaves neck & scolex.
9. Scolex attaches to inside of host intestine.
10. Neck begins to bud off segments that become proglottids.
11. 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

-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.
-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

-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

-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):
*look like rice grains (cucumber seeds).
*move around in feces.
*shed in “egg packets”.
*each packet contains ~a dozen eggs.


Dipylidium caninum

-Scolex: has 4 suckers, rostellum w/ several rows of hooks.
-Up to 50 cm (20”), usually 6” or more.
*absorb nutrients through skin.
*feeds on material passing through intestines.
*do NOT suck host's blood


Dipylidium caninum
Life Cycle - Direct or Indirect

*IH: fleas (usually), lice


Dipylidium caninum
Predilection Site

Small Intestine


Dipylidium caninum
Prepatent Period

2 to 3 weeks


Dipylidium caninum
Life Cycle

1. Perianal region of infected dog or cat becomes contaminated w/eggs from feces.
2. Larval flea or louse (IH) ingests eggs.
3. Cysticercus (metacestode) develop in IH & becomes infective.
*usually occurs in muscle of IH.
4. Dog or cat ingests IH while grooming.
5. Cysticercus (metacestode) goes to intestine of DH.
6. In intestine, matures & develops proglottids.
7. Gravid proglottids containing eggs develop in ~2 weeks.
8. 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

-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:
*NOT in packets.
*single eggs seen in feces.
*thick striated shells.


Taenia pisiformis

-Scolex: has 4 suckers, rostellum w/2 rows of hooks.


Taenia pisiformis
Life Cycle - Direct or Indirect

*IH: rabbits, hares


Taenia pisiformis
Predilection Site

Small Intestine


Taenia pisiformis
Prepatent Period

1 to 2 months


Taenia pisiformis
Life Cycle

1. Gravid proglottids containing eggs are passed in dog feces.
2. Proglottids crawl around in feces onto surrounding vegetation.
3. Eggs released from proglottids in envrio.
4. Rabbit ingests eggs on vegetation or in feces.
5. Egg hatches in sm intestine of rabbit & travels to liver via blood.
6. Develops into cysticercus (metacestode) in rabbit.
7. Cysticercus usually forms dormant cyst in rabbit.
8. Dog eats rabbit
9. The cysticercus (often encysted) attaches to sm intestine of dog & matures there.
10. 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

-Proglottids or eggs in feces.
-Proglottids are much larger & more rectangular than those of D. caninum.


Taenia taeniaeformis
What animal(s) does it infect?



Taenia taeniaeformis
Life Cycle - Direct or Indirect

*IH: rodents


Class Digenea
General Characteristics

-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 (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

-Matures in bile duct of host.
-Leaf shaped.
-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

*IH: snail


Fasciola hepatica
Predilection Site

Bile Duct


Fasciola hepatica
Prepatent Period

8 to 10 weeks


Fasciola hepatica
Life Cycle

1. Adult live in bile ducts of mammalian host.
2. Eggs produced by adult go through intestines & are excreted in feces.
3. In the enviro, egg hatches to release a ciliated miracidium.
*juvenile form.
*2 to 4 weeks after excretion.
4. Miracidium penetrates the first IH.
*if it doesn't find an IH in 24 hours, it dies.
5. In the snail, the miracidium discards its ciliated “skin” & metamorphoses into a simple form called a sporocyst.
6. 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.
7. Redia develop into cercaria.
*1 to 2 months.
*has a tail to aid in swimming.
8. Cercaria leaves the snail & enters surrounding water.
9. 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.
10. Grazing mammal ingests plants containing metacercaria.
11. Metacercaria is digested in mammalian host's sm intestine.
12. Forms a young, which invades host's liver.
13. In several weeks, young flukes migrate to host bile ducts.
14. Mature into adult flukes in bile ducts.
15. Complete life cycle takes 3 or 4 months (summer).
16. 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

-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

*oval, golden brown.
*coughed up & swallowed.


Paragonimus kellicotti

-Oval, reddish brown
-About 14 x 7 mm (about 1/2”)
-Visible operculum (lid).


Paragonimus kellicotti
Life Cycle - Direct or Indirect?

*IH1: snail
*IH2: crayfish or crabs


Paragonimus kellicotti
Life Cycle

1. Eggs shed in feces of infected animal.
2. Eggs hatch in water & miracidium emerges.
3. Miracidium infects snail.
4. Develops into cercaria in the snail.
5. Cercaria leaves snail & infects a crayfish.
6. Develops into metacercaria in the crayfish.
7. Dogs & cats become infected when they eat infected crayfish.
8. Young flukes pass through intestinal wall & invade lungs.
9. Mature & produce eggs in lungs (in cysts).
10. Eggs are coughed up & swallowed, excreted in feces.


Paragonimus kellicotti
Symptoms & Disease

-Chronic, deep, intermittent cough.
-Weak, lethargic.
-May be asymptomatic.


Paragonimus kellicotti

-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.