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Epidemiology of Nematodes, Cestodes, and Trematodes 127

Source: Centers for Disease Control and Prevention (CDC) Source: Centers for Disease Control and Prevention (CDC)

FIGURE 5-8 Eggs of two Taenia spp. species, FIGURE 5-9 Scolex of Taenia solium cestodal
T. solium and T. saginata, are indistinguishable tapeworm
from each other

whereas heavier infections may produce abdominal diagnosing infestation with tapeworms is based on the
discomfort, epigastric pain, vomiting, and diarrhea. recovery and identification of eggs by microscopy or vis-
T. solium eggs can also infect humans and cause cysti- ible proglottids in stool specimens or from the perianal
cercosis (larval cysts in lung, liver, eye, and brain), result- area. Antibodies are also produced against the organisms
ing in blindness and neurological disorders (Figure 5-8). found in cysticercosis and are useful epidemiological
The incidence of cerebral cysticercosis can be as high tools by immunological testing as an indirect method of
as 1 per 1,000 population and may account for up to identifying the causative organism. Cysticercosis may be
20 percent of neurological case in some countries (e.g., confirmed by the presence of antibodies against the spe-
Mexico); cysticercosis ocular involvement occurs in cific organism as a definitive diagnosis.
about 2.5 percent of patients and muscular involvement As members of the Platyhelminths, the cestodes, or
is as high as 10 percent (India). tapeworms, possess many basic structural characteristics
Prevention and control of cestodal infections re- of flukes, but also show substantial differences. The single
quires proper harvesting, treatment, and storage of meat. most striking difference, however, is that the cestodes con-
A thorough inspection of beef and pork and adequate sist of segments called proglottids and those of the flukes
cooking or freezing of meat are effective precautions do not. And whereas flukes are flattened and generally
against transmitting the disease through the distribution leaf-shaped, adult tapeworms are flattened and elongated.
of food, because cysticerci do not survive temperatures In addition, tapeworms differ from flukes in that they may
°
°
below –10 C and above 50 C. Treatment of breeding be quite long as they vary in length from 2 to 3 mm to
stock and exercising care in procuring food for these 10 m, and may have as few as three segments up to sev-
animals will aid greatly in controlling outbreaks. For eral thousand segments. Edward Tyson, a British scientist
an infected person, praziquantel is the drug of choice. and physician, was the first to recognize that the tapered
Passage of the scolex or head of the tapeworm from the end of the worm was the head. Although Tyson mainly
intestines must be accomplished in order to confirm a concentrated on the roundworm called Ascaris lumbri-
satisfactory treatment (Figure 5-9). coides, he contributed the first detailed work on the mor-
phology of the tapeworms, or cestodes, of humans. His
Pathology and Immunology of work can be considered as marking the beginning of a
Tapeworm Infections subdiscipline of parasitology called helminthology, which
reached a peak in the nineteenth century. It was also dur-
Gastrointestinal symptoms are due to the presence of ing this period that the first real attempts were made to
the tapeworm. Cysticercosis symptoms are a result of understand the infections caused by the various parasites
inflammatory/immune responses. The chief method for and methods of diagnosis and treatment.