Page 198 - parasitology for medical and clinical laboratoryprofessionals

178 CHAPTER 7

is the major diagnostic procedure for D. caninum. Treatment and Prevention
However, neither the scolex nor the proglottids are
found in many cases of the infection when examining Although praziquantel has been found to be somewhat ef-
stool specimens. Therefore, finding eggs is the most fre- fective, niclosamide is the drug of choice. Good veterinary
quent manner of diagnosis. care of cats and dogs by keeping the animals free of parasites
Larvae mature in the intestine but are not the chief and fleas (ectoparasites) is essential. Control of other insects
stage in which D. caninum is identified. The egg packets such as beetles may aid greatly in the prevention of infec-
and gravid proglottids are the most diagnostic stages tions by D. caninum. Personal hygiene is also paramount in
found in the laboratory. preventing hand-to-mouth ingestion of infected fleas.

SUMMARY

Cestodiasis, a term used for tapeworm infections, may bladderworms and when infected meat of the intermedi-
occur from infections with up to 40 species of adult ate host is eaten, cysticerci are released and attach to the
worms and perhaps 15 larval forms. Humans are most gut wall of the final host where they develop into adult
often incidental or accidental hosts, meaning that they tapeworms.
are not definitive hosts. Disease from tapeworm infec- Cestodes are hermaphroditic, with both male and
tions usually results from eating uncooked meat from de- female reproductive systems in each segment. The pro-
finitive hosts infected with the various cestodes. glottids nearest the scolex are immature, but the pro-
Cysticercosis is another term for an infection by glottids near the caudal end are called gravid (pregnant)
cestodes, contracted mainly by the eating of contaminated proglottids and contain many eggs.
meat and its by-products and wastes. After ingestion Taenia tapeworms include two human species,
of the eggs, they hatch in the stomach of the host. The Taenia saginata (beef) and T. solium (pork). These
resulting larvae penetrate the intestinal wall and circulate two taeniid tapeworms were originally thought to be
throughout the body systems of the host, frequently one species, until research proved otherwise. The
involving the brain. Neurocysticercosis, of which there T. solium variety of the taeniid tapeworm is the cause of a
are four types, occurs in larval death, which results in a major complication called cysticercosis. T. solium is both
strong immune response to inflammation. Sizes of lesions an intestinal as well as a tissue-infective organism. The
vary from 1 cm up to 7 cm in diameter, and are viewed cysticercus resembles a bladder, giving rise to the term
via radiological procedures such as magnetic resonance bladderworms.
(MR) and computerized tomography (CT). These cysticerci are known to encyst the heart,
Taeniid and diphyllobothriid tapeworms are brain, or eye, and muscles. The adult stages of T. solium
among the most important cestodes implicated in human and T. saginata rarely cause any overt signs or symp-
disease. The adult tapeworm has no digestive tract, and toms. Another cyst-forming organism is Echinococcus
nutritive substances enter the tapeworm across the mem- granulosus. E. granulosus may form cysts in the tissues
branes structure covering the segments and excretion of of the central nervous system of dogs, causing seizures in
digestive wastes is accomplished through a specialized the canine similar to those of the species of cestodes that
structure called a “flame cell.” The proglottids or seg- may infect the human brain.
ments of the tapeworm, are attached to a scolex or head, It is evident that most of the cestodal infections re-
on which mechanisms for attachment to the intestinal late to eating various types of meats. Diphyllobothrium
wall are found. Mature proglottids contain numerous latum is an organism called the fish tapeworm, which
eggs, which are passed into soil or water through defeca- humans harbor as adult parasites in the intestine. Human
tion. Eggs consumed by the intermediate host hatch in eat infected fish, and the plerocercoid develops into an
the intestine, releasing larval stages, or oncospheres that adult tapeworm in the gut, and the cycle is repeated.
burrow through the gut wall to reach various tissues of Early descriptions of the tapeworm were
the host. Here they develop into encysted cysticerci or unreliable due to confusion with the two common