Taenia solium Neurocysticercosis1

Abstract

After many years as a relatively rare neurological disorder, Taenia solium (pork tapeworm) neurocysticercosis is now seen more frequently in patients in the United States. Humans are the definitive and only hosts of the tapeworm stage. The larval stage develops in the pig, the intermediate host, following ingestion of tapeworm eggs excreted in the feces of the tapeworm carrier. The larvae invade most tissues of the pig giving rise to a disease termed cysticercosis. When humans ingest raw or undercooked meat from cysticercotic pigs, taeniasis (tapeworm) results. Humans can also act as intermediate hosts if they ingest T. solium eggs present in contaminated food or water; cysticercosis, similar to that seen in pigs, develops. If the larvae invade the central nervous system, neurocysticercosis with ensuing neurological dysfunction results. Cysticercotic pigs are rarely found in the United States. Only three animals out of >88 million federally inspected pigs were diagnosed as cysticercotic in 1990. In the United States, the excellent sewage disposal system prevents access of pigs to human feces and infection of pigs by T. solium eggs is consequently rare. In Mexico, however, the mean rate for cysticercotic pigs in inspected slaughter houses during 1980–1981 was 1.55% and there is little reason to suspect that it has decreased. In rural areas of Mexico and South America where sewage disposal is limited, the number of cysticercotic pigs can be in excess of 5% and neurocysticercosis is a common disease in the human population. In such areas, pigs are not penned or fed but depend on scavenging waste, including human waste, for food. Thus, the cycle of cysticercotic pigs infecting humans and tapeworm carriers infecting both humans and pigs is difficult to break in primitive rural areas. The incidence of neurocysticercosis is increasing in the United States due to an influx of immigrants from areas where T. solium is endemic. Most patients presenting with neurocysticercosis are of Mexican origin and probably acquired their disease in Mexico. However, several cases have been reported in people who have no history of travel to endemic areas and who were probably infected through ingestion of food prepared by an unhygienic food preparer who was also a tapeworm carrier. In this review, the life cycle of T. solium, parasite transmission, incidence of T. solium-related disease in pigs and humans, the disease process, drugs used in treatment, detection T. solium and destruction of T. solium eggs and cysticerci in foods are discussed. Food microbiologists must be aware of the increasing importance of T. solium as a disease agent and how to control T. solium-related diseases.