Hookworm infection is caused by several species of hookworms, with Ancylostoma duodenale and Necator americanus being the most important (Table 123-2). There are more than 9 million humans worldwide infected with hookworms. Ancylostoma duodenale is the predominant species in Europe, the Mediterranean region, northern Asia, and the west coast of South America. N. americanus predominates in the Western hemisphere, sub-Saharan Africa, Southeast Asia, and the Pacific Islands. Optimal soil conditions and fecal contamination are found in many agrarian tropical countries and in the southeastern United States. Infection typically occurs in young children, especially during the first decade of life. The larvae are found in warm, damp soil and infect humans by penetrating the skin. They migrate to the lungs, ascend the trachea, are swallowed, and reside in the intestine. The worms mature and attach to the intestinal wall, where they suck blood and shed eggs.
Cutaneous larva migrans Ancylostoma braziliense Larval penetration Albendazole or ivermectin or (azoonotic hookworm) (and failure to migrate) thiabendazole topically
Infant ancylostomiasis A. duodenale Perinatal (?) Albendazole or mebendazole or pyrantel pamoate
Intestinal ascariasis Ascaris lumbricoides Ingestion of Ascaris eggs Albendazole or mebendazole or pyrantel pamoate
Diarrhea, malabsorption Strongyloides stercoralis Larval penetration Ivermectin or thiabendazole (celiac-like)
Pinworm Enterobius vermicularis Ingestion of embryonated eggs Albendazole or mebendazole or pyrantel pamoate
Abdominal angiostrongyliasis Angiostrongylus costaricensis Ingestion of contaminated food Mebendazole or thiabendazole
Eosinophilic meningitis Angiostrongylus cantonensis (rat Ingestion of undercooked Mebendazole lungworm) contaminated seafood
Infections are usually asymptomatic. Intense pruritus (ground itch) occurs at the site of larval penetration, usually the soles of the feet or between the toes, and may include papules and vesicles. Migration of larvae through the lungs usually is asymptomatic. Symptoms of abdominal pain, anorexia, indigestion, fullness, and diarrhea occur with hookworm infestation. The major manifestation of infection is anemia. Examination of fresh stool for hookworm eggs is diagnostic. Therapy includes anthelmintic treatment with albendazole, mebendazole, or pyrantel pamoate and treatment for anemia. Eradication depends on sanitation of the patient’s environment and chemotherapy.
Ascariasis is caused by Ascaris lumbricoides, a large nematode. It is the most prevalent helminthiasis, affecting 1 billion people (see Table 123-2). After humans ingest the eggs, larvae are released and penetrate the intestine, migrate to the lungs, ascend the trachea, and are swallowed. On entering the intestines again, they mature and produce eggs that are excreted in the stool and are deposited in the soil, where they survive for prolonged periods.
Manifestations may be the result of migration of the larvae to other sites of the body or the presence of adult worms in the intestine. Pulmonary ascariasis occurs as the larvae migrate through the lung, producing cough, blood-stained sputum, eosinophilia, and transient infiltrates on chest x-ray films.