Page 184 - The Veterinary Laboratory and Field Manual 3rd Edition

Parasitology 153

Coenurosis or gid LIFE cycLE
The intermediate stage (Coenurus cerebralis)
Coenurosis is caused by the intermediate stage develops in the brain and spinal cord of sheep,
(Coenurus cerebralis) of the tapeworm Taenia yak, cattle, other ruminants and has also been
(multiceps) multiceps which occurs in the small found in man. Infection occurs as a result of
intestine of dogs and other canid species such ingestion of ripe segments of Taenia (multiceps)
as the fox and jackal. The adult tapeworm is multiceps usually in grass or water contaminated
40–100 cm long and the gravid segments mea- with infected dog faeces. The embryos hatch in
sure 8–12 mm by 3–4 mm. Coenurus cerebralis is the intestine and are carried in the blood stream
found in sheep, cattle and other ruminants in to the liver (where many die) then to the heart
many parts of the world. The cyst varies in size and finally to the systemic circulation. At about 8
from a pea to a hen’s egg and is composed of a to 14 days after infection the embryos reach the
thin transparent wall on the inner side of which brain. The young cysts wander about in the brain
are a number of small white irregular white before settling down and become fully developed
spots 400 to 500 in number each representing an in 7 to 8 months. The fully grown cyst can mea-
invaginated larval tapeworm head (see Figures sure 5 cm or more in diameter and has a delicate,
3.26 and 3.28). translucent wall. On the inner surface of the cyst

Figure 3.28 Life cycle of Taenia multiceps, the tapeworm parasite that has a cyst stage in the brain caus-
ing ‘gid’ in the ruminant intermediate host. (A) Adult tapeworm in the small intestine of the dog (final or
definitive) host. The adult worm may reach up to 1 m in length. (B) Mature tapeworm segments are passed
in the dog’s faeces and release eggs into the environment. (C) The ruminant intermediate host ingests
the tapeworm eggs while grazing. (D) The larval cyst (Coenurus cerebralis) develops in the brain causing
circling. (E) The dog becomes infected by ingesting infected brain tissue. The parasite is controlled by (1)
treating infected dogs with a drug to kill the adult tapeworm and (2) preventing the dog eating infected
ruminant tissues.

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