335 - Nematode Infections

Abstract

Nematodes of medical importance can be categorized into those that primarily affect the gastrointestinal tract, where adult worms become established and cause disease, and those that affect other tissues and organ systems. The former group includes the roundworm Ascaris lumbricoides, the hookworms Ancylostoma duodenale and Necator americanus, the pinworm Enterobius vermicularis, the whipworm Trichuris trichiura, and the threadworm Strongyloides stercoralis. Nematodes that invade and cause disease primarily in tissues outside the gastrointestinal tract include those that cause lymphatic filariasis (Wuchereria bancrofti, Brugia malayi, and Brugia timori), Onchocerca volvulus, Loa loa, the guinea worm Dracunculus medinensis, and Trichinella and Angiostrongylus species. Nematode infections are rarely fatal; they more commonly result in chronic morbidity such as iron deficiency anemia caused by hookworm or blindness due to onchocerciasis. Nematode infections are prevalent in the temperate and tropical regions of Africa, Asia, and Latin America. They are transmitted by the oral ingestion of embryonated eggs or by penetration of infective larvae through the skin, either by direct contact with contaminated soil or by the bite of an arthropod vector. Nematode infections are most common in areas with poor sanitation, where the environment is contaminated by human feces, and in climates that support survival of the insect vector if one is involved in the life cycle.