Lab 4: Cestodes

The Tapeworms!

General anatomy of a tapeworm

• Tapeworms are long, segmented, flattened & ribbonlike

• On extreme anterior end is the scolex or the head. This is the holdfast organelle.

• The scolex has 4 suckers called acetabula

• Some tapeworms are armed with rostellum, backward-facing hooks that help anchor the worm in the small intestine.

• Posterior to scolex is the strobila or the neck – this is where the proglottids, or segments, are formed.

• The proglottids closest to the scolex are immature, those farthest are gravid - the oldest.

Tapeworm Reproduction• Tapeworms are hermaphroditic, the

proglottids contain both male & female sex organs.

• Cross-fertilization & self-fertilization occur between/within individual proglottids

• Gravid proglottids are “spent” and contain only a uterus filled with egg packets. They may break off and exit via feces or around anus. Can be seen with the naked eye.

• Proglottids rupture in external environment & release thousands of hexacanth embryos.

• Hexacanth embyros have six hooks.

Better picture on page 72 of textbook

Dipylidium canninum: “cucumber seed tapeworm”

• Most common tapeworm of both dogs & cats because the intermediate host is the flea

• Fleas often contain the infective metacestode (larval) stage: cysticercoid

• Scolex is armed & has prominent proboscis covered w/ hooks

• Terminal proglottids are motile and look like moving cucumber seeds on the stool or around anus

Dipylidium canninum: “cucumber seed tapeworm”

(cont’d)• Terminal proglottids

contain thousands of egg packets, each containing 20-30 hexacanth embryos

• Prepatent period is 14-21 days

Dipylidium canninum: Life cycle

Dog, cat becomes infectedby ingesting fleas thatare infected with cysticercoid larval stage

Also important to note thatthese are ZOONOTIC!

Dipylidium canninum: Control

• Flea control is the number one way to prevent tapeworm infection

• Treatment is usually with a single dose of praziquantel (Droncit)

Taenia spp.

• 2nd most common type of tapeworm seen in clinics

• Segments are more rectangular shaped

• Also zoonotic

• Intermediate hosts are rodents & rabbits

• Seen more frequently in cats than in dogs

Taenia spp.: Anatomy

• Scolex is armed with 2 rows of hooks or acetabula

• Also manifests with motile terminal proglottid segments that may appear on feces or around anus

Taenia spp.

• Terminal proglottids contain eggs with hexacanth embryos (not egg packets!)

• Striated eggshell, slightly oval shaped & contain single oncosphere with three pairs of hooks

Taenia spp.: Life Cycle

• Metacestode (larval) stageis cysticercus: bladder wormfound in intermediate host

•Embryos develop into cysticercus in peritoneal cavity of intermediate host •One cysticercus=one adulttapeworm

•More pathogenic to intermediate host than to definitive host

Echinococcus granulosis &E. multilocularis:

Hydatid disease tapeworms• E. granulosis = dogs, encysts in

viscera & brain

• E. multilocularis = cats, encysts in lungs & alveoli

• Has only 3 proglottids, very small

• Eggs are very similar to Taenia spp. – adult must be identified

• EXTREME ZOONOTICPOTENTIAL!!!!!

Echinococcus granulosis &E. multilocularis

• Hydatid cysts result in thousands of scolex

• Size is impingent on organs• Damages area where it

resides (brain, liver, lung)• Neoplastic lesions can

grow as large as a human head

• Can kill host if burst open, causes anaphylaxis

• Wild herbivores are intermediate hosts

Anoplocephala spp.: Equine tapeworms

• Most common equine tapeworm

• Lives in small & large intestine, occasionally in stomach

• Proglottids are wider than they are long

• Intermediate host is grain mite & occasionally beetles

Monezia spp.• Infect intestinal tract of cattle,

sheep & goats

• Scolex is unarmed

• Proglottids are very short & wide

• Eggs are square or triangular shaped, possess a pyriform apparatus (pear-shaped)

• Intermediate host is oribatid grain mites

• Can cause GI stasis in calves

• Can cause ulcerative lesions where attached

Diphyllobothrium latum: Broadfish tapeworm

• Pseudotapeworm w/ zoonotic potential

• Continually release eggs until exhausts uterine contents

• Terminal proglottids become senile rather than gravid and detach in chains

• Eggs are light brown, oval & possesses single operculum at one pole

• Eggs are unembryonated when passed in feces

Diphyllobothrium latum

• Tapeworm of fish-eating mammals

• Has 2 intermediate hosts, copepod & fish

• Encysts in fish muscle• Larvae develop on

intestinal wall

Identify!

Identify!

Identify!