Class Cestoda (tapeworms)

T/F: Like trematodes, tapeworms are also flatworms

True

Cestodes are ribbon-like and divided into a long chain of ___________ behind a __________.

Proglottids, scolex

The entire chain of proglottids

strobila

Why are tapeworm eggs not commonly found in fecal flotation solutions?

Eggs are contained within the proglottids, which are shed intact into the feces

T/F: Proglottids can only be observed microscopically

False, they can be seen with the naked eye

The area of cell division behind the scolex which gives rise to proglottids or segments

neck

How do tapeworms obtain nutrients?

By diffusion across the tegument, there is no digestive tract

The organ used by the tapeworm to hold on to the lining of the small intestine

Suckers (they have 4)

Organelle that some tapeworms possess that has backwards-facing hooks to anchor itself into the mucosa

Rostellum

The larva within each egg

hexacanth embryo or oncosphere (L1)

The thick, dark, radially striated shell of the egg

embryophore

The infective stage of cestodes

L2 within the intermediate host

What are the three forms of the L2 larval stage

1. Cysticercus/bladderworm - invaginated inside the bladder

2. Hydatid cyst - large, encapsulated cyst

3. Cysticercoid - unique to arthropod intermediate hosts, the scolex is depressed within a small cyst

Common name of Dipylidium caninum

Flea tapeworm, double-pored tapeworm

Host of Dipylidium caninum

dogs, cats

Intermediate host of Dipylidium caninum

Fleas (Ctenocephalides spp. and Pulex irritans) or more rarely the biting louse (Trichodected canis)

Site of D. caninum

Small intestine

Prepatent period of D. caninum

2-3 weeks

Pathogenesis of D. caninum

Possible enteritis

Clinical signs of D. caninum

Often asymptomatic; diarrhea, increased appetite, licking hte perineum, scooting (rule out anal gland problems)

Indentification of D. caninum

Finding tapeworm segments on the host’s perineum or in the feces, fecal float

Control of D. caninum

Eliminate the intermediate hosts; educate the client!

T/F: D. caninum is zoonotic

True, it is metazoonotic (by ingesting flea or louse)

Common name of Taenia spp.

Single pored tapeworm; dog/rodent/rabbit tapeworm

Host of Taenia spp.

Dogs

Intermediate host of Taenia spp.

Rabbits and rodents

Site of Taenia pisiformis

Small intestine

Prepatent period of Taenia pisiformis

1.5-2 months

Identification of Taenia pisiformis

FF, CM (seen only if proglottids break open), segments on anal fur and bedding

Common name of Taenia taeniaeformis

Cat/rodent/rabbit tapeworm, single-pored tapeworm

Host of Taenia taeniaeformis

Cats

Site of Taenia Taeniaeformis

Small intestine

Intermediate host of T. taeniaeformis

rodents (rats, mice and rabbits)

Prepatent period of T. taeniaeformis

1 month

Pathogenesis of Taenia spp.

enteritis, possible intestinal obstruction due to length

Clinical signs of Taenia spp.

similar to D. caninum with addition of intestinal obstruction

Control of Taenia spp.

Eliminate access to intermediate hosts

Why does Taenia spp. present a greater risk of obstruction?

Adults in the small intestine are more than twice as long as D. caninum (3-4 ft vs 1 ft)

How to record the ova of Taenia spp.

Taeniid-type

How many genital pores does Taenia spp. have on each proglottid?

1 (D. caninum has two)

What are two reasons you should differentiate D. caninum from Taenia spp.?

1. Different intermediate hosts make different control measures and client education necessary (Flea control vs rabbit/rodent control)

2. Dewormers effective for Taenia spp. are not always effective in eliminating D. caninum)

Common name of Taenia saginata

Cosmopolitan beef tapeworm

Host of Taenia saginata

Humans

Clinical signs of T. saginata

Rare; hunger pangs and diarrhea

Method of transmission of T. saginata

Humans become infected with this tapeworm by eating undercooked, infected beef containing infective cysticerci

Common name of Taenia solium

Pork tapeworm

Host of Taenia solium

Humans

Method of transmission of Taenia solium

Humans become infected by eating undercooked, infected pork containing the cysticerci

Pathogenesis of Taenia solium

Blindness from ocular migration or neurological disease from migration in the CNS

Multiple, extremely invasive, thin-walled, fluid filled cyst

A multiocular cyst

Common name of Echinococcus spp.

Hydatid tapeworm

How many proglottids do Echinococcus spp. possess?

3; immature, mature and gravid

T/F: The eggs are distinct from Taenia spp. ova

False, cannot be differentiated

How do humans become infected with Echinococcus spp.?

By accidentally ingesting infective eggs shed by infective foxes, coyotes, and occasionally dogs and cats

Echinococcus spp. larval stage is the causative agent of what disease in humans?

alveolar hydatid disease; where metastasis of hepatic cysts to the lung and brain commonly occur; often fatal

Definitive host of Echinococcus spp.

Fox

The definitive antemortem diagnosis

Administer a purgative to the host and examinr the feces for adults (PPE!!)

Common name of Anoplocephala perfoliata

Equine tapeworm

Host of Anoplocephala perfoliata

Horses and donkeys

Intermediate host of Anoplocephala perfoliata

Oribatid mites (forage/grain mites)

Site of A. perfoliata

ileocecal junction (adults tend to cluster around the ileocecal valve)

Pathogenesis of A. perfoliata

Usually nonpathogenic, but ulceration may lead to performation of the cecum, leading to peritonitis and death

Identification of A. perfoliata

Fecal float, CM

Clinical signs of A. perfoliata

Colic, diarrhea, unthriftiness, possible death from a ruptured cecum

Common name of Monezia spp.

Ruminant tapeworm

Intermediate host of Moniezia spp.

oribatid mites

Site of Moniezia spp.

Small intestine

Identification of Monezia spp.

Fecal float

Common name of Hymenolepis nana

Dwarf tapeworm (of humans)

Common name of Hymenolepis diminuta

Rat tapeworm

Intermediate host of Hymenolepis spp.

Beetles

Site of Hymenolepis spp.

The small intestine

Identification of Hymenolepis spp.

Fecal flotation (ova shed intermittently)

Common name of Diphyllobothrium latum

Broad fish tapeworm

Host of Diphyllobothrium latum

Dogs, pigs, bears, humans

Intermediate host of Diphyllobothrium latum

Aquatic copepod crustaceans (plankton-like organisms) are the primary intermediate host

Various fish are the secondary intermediate hosts

Site of D. latum

small intestine

Identification of Diphyllobothrium latum

Ova found via fecal sedimentation test

What can D. latum cause in humans and occasionally dogs

Pernicious anemia from vitamin B-12 deficiency

What three parasites can be transmitted by feeding raw fish to dogs?

Diphyllobothrium latum (broad fish tapeworm)

Dioctophyma renale (giant kidney worm)

Nanophyetus salmincola (vector of Neorickettsia helminthoeca, salmon poisioning)