Cestodes Causing CNS Disease
Taenia multiceps multiceps is an intestinal parasite of canids (especially dogs, foxes, and jackals) and occasionally people. Its intermediate hosts include sheep, goats, deer, antelope, chamois, rabbits, hares, horses, and less commonly cattle, which acquire this tapeworm's eggs while grazing. After ingestion, some oncospheres hatch and reach the brain, developing by endogenous budding into a metacestode (larval) stage known as Coenurus cerebralis. Initial invasion and development of the oncospheres may be responsible for acute suppurative meningoencephalitis. The fully developed coenurus may be 5–6 cm in diameter and cause increased intracranial pressure, which results in ataxia, hypermetria, blindness, head deviation, stumbling, and paralysis. This clinical condition is colloquially known as gid, sturdy, or staggers. In sheep, palpation of the skull caudal to the horn buds may reveal refraction; surgery to remove the cyst, including its wall, has a reasonable chance of success and is justified in valuable animals. Dogs associated with sheep and other livestock should not be fed the brain or spinal cord from infected animals and should be dewormed regularly.
Taenia solium is a tapeworm found in the small intestine of people. Its metacestode (larval) stage, a cysticercus, is a large fluid-filled cavity or vesicle or bladder found in the musculature of pigs. This larval stage was once regarded as a separate parasite, and it still retains the scientific name Cysticercus cellulosae. In people, this larval stage usually develops in subcutaneous sites and musculature but may be found in nervous tissues, eg, the brain and ocular tissues. Infection in people stems from ingestion of tapeworm eggs in contaminated foods or from dirty hands. In the brain, the parasite usually develops in the ventricles. Infection causes pain, paralysis, epileptiform seizures, locomotor disturbances, and possibly death. The larval cysticerci commonly localize on the meninges and in the neuropil. Treatment of human cysticercosis is by surgical removal of the lesion; however, the prognosis is poor.
Echinococcus granulosus is a tapeworm found in the small intestine of the canid definitive host. Its eggs are ingested by the intermediate hosts, wild and domestic herbivores, eg, sheep, cattle, and moose. People can also serve as intermediate hosts. After hatching in the intestine of the intermediate host, the oncospheres invade the circulatory system and lodge in various organs (the liver and lungs), where they develop into large, thick-walled, unilocular hydatid cysts that bud protoscolices endogenously. Hydatids have been rarely reported in the CNS of domestic animals and are rare in people, in which they produce symptoms similar to those of a brain tumor.
Foxes are the definitive host for a related species, Echinococcus multilocularis. Microtine rodents (such as voles) are the intermediate hosts. This parasite has been rarely found in the brain of people, in which the invasive, thin-walled multilocular hydatid cysts produce innumerable exogenous daughter cysts that bud protoscolices. Surgical intervention is more successful in removing unilocular hydatid cysts of E granulosus.