Page 140 - Medical Parasitology_ A Textbook ( PDFDrive )

Cyclophyllidean Tapeworms 133

Habitat
The adult tapeworm resides in the small intestine of the host.

Morphology
The adult worm in the intestine is about 10–70 cm long. The scolex has 4 prominent
suckers and a retractile rostellum with up to 7 rows of spines. It has 60–175 melon
seed-like proglottids. The mature proglottid has 2 genital pores, one on either side.
Gravid proglottids which contain packets of eggs enclosed by capsules are passed
out of the anus of the host singly or in groups.

Life Cycle (Fig. 11.12)
(1–2) The eggs or proglottids passed out in faeces of dogs and cats are eaten by
larval stages of dog flea (Ctenocephalides canis) and cat flea (C. felis). (3) The
oncospheres hatch and penetrate the intestinal wall to develop into cysticercoid in
the body cavity of the flea larva. (4) Adult fleas harbour the infective cysticercoid.
(5–7) Definitive hosts including humans are infected by ingesting fleas containing
cysticercoid. (8) Adult worm develops with scolex attached to the small intestine.

4
Adult flea harbours
i the infective cysticercoid. Humans, normally children,
Cysticercoid 7 acquire the infection by
5 ingesting the infected flea.
Host is infected
Infected larval by ingesting fleas
stage develop containing cysticercoid.
into adult flea.
6

Oncosphere Cysticercoid
Scolex attaches
Oncospheres hatch from Animals can transmit the in intestine
the eggs and penetrate the infected fleas to humans.
intestinal wall of the 3
larvae. Cysticercoid larvae
develop in the body cavity. Gravid proglottids are
passed intact in the faeces
1 or emerge from perianal
region of either animal
or human hosts.
2 8 Adult in small intestine
d
Eggs packets containing Each proglottid contains egg packets
embryonated eggs that are held together by an outer
are ingested by larval embryonic membrane (see 2 ).
stage of flea. The proglottids disintegrate
and release the egg packets.
i = Infective Stage
d = Diagnostic Stage
Fig. 11.12 Life cycle of Dipylidium caninum (Reproduced from https://www.cdc.gov/dpdx/dipy-
lidium/index.html)