Page 181 - The Veterinary Laboratory and Field Manual 3rd Edition

150 Susan C. Cork and Mani Lejeune

intestinal wall and migrate to suitable parts of Cysticercosis
the body such as muscle, lung or liver where
they develop into a cyst. The cysts of some tape- Taenia sp. tapeworms are distributed worldwide.
worm (Taeniidae) contain a fluid filled cavity Although the final host is usually a carnivore or
omnivore there is usually little sign of disease
with one or more heads, this is called a blad- caused by the adult tapeworm in these species.
der worm (Cysticerci, Coenurus, hydatid cyst). The main clinical concern is the cystic stage
These larval forms are illustrated in Figure 3.26. which develops in the intermediate herbivore
When the definitive host eats part (or all) of the or omnivore host, for example: Taenia saginata
intermediate host in which the bladder worm or adult parasite occurs in the intestine of humans
cysts are situated, the heads of the larval worm and the cysts occur in cattle (Figure 3.27).
attach themselves to the intestinal wall of the The adult of T. solium occurs in the intestine of
final host and develop into an adult tapeworm. humans and the cysts occur in various organs
The intermediate hosts of Anoplocephala sp. of swine. Other species cause cysts in rabbits
tapeworms are invertebrates such as free-living and rodents and the adult parasite occurs in the
mites that are ingested accidentally while horses intestine of carnivores such as dogs and cats
are feeding or grazing. In dogs and cats the tape- (see Table 3.5).
worm Dipylidium caninum is transmitted by the
flea which may be ingested accidentally by dogs LIFE cycLE
and cats while grooming. Most species can be The adult tapeworm lives in the small intestine
infected with tapeworms without showing obvi- of a definitive host (for example, human for
ous clinical signs. In cattle, adult Moniezia sp. T. saginata). The mature worms can be up to 10m
tapeworms may occur in fairly high numbers long and have a life span of more than 20 years.
without causing any significant clinical disease Each tapeworm can produce 400 segments each
but in horses, adult Anoplocephala sp. tapeworms containing 8000–50,000 eggs. The eggs, or the
are occasionally reported to cause significant segments containing the eggs, are passed with
damage with occasional perforation of the intes- the faeces of a definitive host and contaminate
tinal wall. There are a range of products available soil, pastures, hay or drinking water and can sur-
to kill adult tapeworms but not all of the prod- vive in the environment for 4 to 6 months. If
ucts used to treat roundworms contain suitable ingested, the egg hatches in the stomach of the
active compounds. The local veterinary officer or intermediate host releasing embryo that cross
animal health advisor can usually provide advice the intestinal wall, enter the blood stream and
on selecting a suitable product. then localize in the muscles or internal organs
The following are some of the important throughout the body to form cysticerci. It can
diseases associated with tapeworms or, more take 10 to 12 weeks for cysticerci to develop in
commonly, their cysts that have been frequently the intermediate host and become infective. In
reported in livestock. In some cases confusion some cases, cysticerci can also develop in the
has arisen due to the fact that the adult tape- final host (for example, Taenia solium in humans)
worm and the cyst stage have had different by accidental ingestion of eggs in contaminated
names, this was initially due to the fact that it food. A final host usually develops infection
was not known that both were part of the same by eating raw tissues which contain tapeworm
life cycle. cysts (Figure 3.27). In the case of T. solium, the
principal location of the cysticerci is the muscle
tissue of the pig (or rodent, bear and so on), but
the cysticerci may also develop in other organs

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