Page 180 - The Veterinary Laboratory and Field Manual 3rd Edition

Parasitology 149

immitis) of animals. Dirofilaria immitis is a common tem of cats and dogs. Stephanofilaria spp. have
parasite of dogs in areas where the intermediate predilection to skin of cattle.
hosts (mosquitoes) are prolific. Adult worms
live in the large blood vessels and chambers of tHE tHorny HEadEd WorMS
the heart. Clinical signs include coughing and The Acanthocephala (thorny headed worms)
congestive heart failure in the later stages of the include Macracanorhynchus hirudinaceus which
disease. Treatment may be difficult due to the inhabits the small intestine of the pig. The para-
location of the parasites and the risk of block- site has an indirect life cycle using the millipede
age of important blood vessels if the worms die. as the intermediate host. Members of this phy-
The control of the disease requires routine pre- lum are pathogenic particularly to water fowls.
ventative treatment with an anthelmintic and
the control of the mosquito intermediate host.
Parelaphostrongylus tenuis is a meningeal worm diseases caused by cestodes
of white tailed deer and camelids/horses are
aberrantly infected with this helminth. Setaria Adult tapeworms are usually found in the
digitata commonly dwells in the peritoneal cav- small intestine of a ‘final’ host but require an
ity of sheep but their larval migration can cause intermediate host, which may be a vertebrate
cerebrospinal nematodiasis. Onchocerca cervicalis or an invertebrate, to complete their life cycle.
is found in the ligamentum nuchae of horses and Tapeworm eggs hatch when they are swallowed
mules. Brugia phangi resides in the lymphatic sys- by the intermediate host. They penetrate the

Figure 3.26 Larval (cyst) forms of some
tapeworms. These are the immature stages of
the tapeworm life cycle that occur in the tissues
of the intermediate host. (A) Cysticercus with a
single invaginated (inverted into the cyst space)
scolex (head), (B) cysticercoid with a single
evaginated scolex, (C) coenurus, (D) hydatid
cyst, (1) endogenous cyst, (2) brood capsule,
(3) protoscolex, (4) cyst wall, (E) Strobilocercus.

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