Page 183 - parasitology for medical and clinical laboratoryprofessionals

Intestinal Cestodes 163

common for asymptomatic infections to occur but a sig- are surrounded by edema, which does not yield suitable
nificant number of patients exhibit seizures, increased images with CT.
intracranial pressure, focal neurologic abnormalities, and The most important cestodes belong to two groups:
various levels of altered mental status. the taeniid and diphyllobothriid tapeworms. The char-
Four forms of neurocysticercosis are described as acteristic taeniid adults, which can reach a length of
pathological conditions of humans: meningeal, paren- several meters, live in the intestine, attached by a scolex
chymal, ventricular, and mixed. In each of these ana- and shed mature proglottids (“segments”) containing
tomic areas, the death of the larval stages stimulates an numerous eggs that pass out into the soil or water, at
extremely strong inflammatory response. Sizes of lesions which time the enclosed eggs are released. When an
vary from small ones of approximately 1.5 cm to larger intermediate host consumes the eggs, they hatch in the in-
cysts that range from 4 to 7 cm in diameter. Cysts may be testine and then release larval stages called oncospheres.
visualized as calcified lesions most effectively and accu- These developmental forms burrow through the gut wall
rately by CT (computerized tomography) but the disad- to reach various tissues of the host, where they develop
vantage of this method is due to significant exposure to into encysted cysticerci or bladderworms. The life cycle
X-rays. An imaging procedure called magnetic resonance is complete when undercooked or raw meat is eaten and
(MR) is sometimes used for demonstrating these calci- the cysticerci are released and attach to the gut wall of the
fied lesions, a process that is beneficial when the lesions final host, developing into adult tapeworms (Figure 7-2).

Source: Centers for Disease Control and Prevention (CDC)

FIGURE 7-2 Life cycle of diphyllobothrium spp.