Life Cycle:
The infective larval stages of the anthropophilic hookworms live in a developmentally arrested state in warm, moist soil. Larvae infect humans either by penetrating through the skin (N. americanus and A. duodenale) or when they are ingested (A. duodenale). Larvae entering the human host by skin penetration undergo extraintestinal migration through the venous circulation and lungs before they are swallowed, whereas orally ingested larvae may undergo extraintestinal migration or remain in the gastrointestinal tract. Larvae returning to the small intestine undergo 2 molts to become adult sexually mature male and female worms ranging in length from 5 to 13 mm.
Epidemiology:
Hookworm infection is 1 of the most prevalent infectious diseases of humans, affecting an estimated 576 million individuals worldwide. Because of the requirement for adequate soil moisture, shade, and warmth, hookworm infection is usually confined to rural areas, especially where human feces are used for fertilizer or where sanitation is inadequate. Hookworm is an infection associated with economic underdevelopment and poverty throughout the tropics and subtropics. Sub-Saharan Africa, East Asia, and tropical regions of the Americas have the highest prevalence of hookworm infection.
Pathogenesis:
The major morbidity of human hookworm infection is a direct result of intestinal blood loss. Adult hookworms adhere tenaciously to the mucosa and submucosa of the proximal small intestine by using their cutting plates or teeth and a muscular esophagus that creates negative pressure in their buccal capsules. At the attachment site, host inflammation is downregulated by the release of anti-inflammatory polypeptides by the hookworm. Rupture of capillaries in the lamina propria is followed by blood extravasation, with some of the blood ingested directly by the hookworm.
Clinical Manifestations:
Chronically infected children with moderate and heavy hookworm infections suffer from intestinal blood loss resulting in iron deficiency,which can lead to anemia as well as protein malnutrition. Prolonged iron deficiency associated with hookworms in childhood can lead to physical growth retardation and cognitive and intellectual deficits.
Anthropophilic hookworm larvae elicit dermatitis sometimes referred to as ground itch when they penetrate human skin. The vesiculation and edema of ground itch are exacerbated by repeated infection. Infection with a zoonotic hookworm, especially A. braziliense, can result in lateral migration of the larvae to cause the characteristic cutaneous tracts of cutaneous larva migrans . Cough subsequently occurs in A. duodenale and N. americanus hookworm infection when larvae migrate through the lungs to cause laryngotracheobronchitis, usually about 1 wk after exposure. Pharyngitis also can occur.
Intestinal hookworm infection may occur without specific gastrointestinal complaints, although pain, anorexia, and diarrhea have been attributed to the presence of hookworms. Eosinophilia is often first noticed in early gastrointestinal infection. The major clinical manifestations are related to intestinal blood loss. Heavily infected children exhibit all of the signs and symptoms of iron deficiency anemia and protein malnutrition. In some cases, children with chronic hookworm disease acquire a yellow-green pallor known as chlorosis.
An infantile form of ancylostomiasis resulting from heavy A. duodenaleinfection has been described. Affected infants experience diarrhea, melena, failure to thrive, and profound anemia. Infantile ancylostomiasis has significant mortality.
Eosinophilic enteritis caused by A. caninum is associated with colicky abdominal pain, usually exacerbated by food, which begins in the epigastrium and radiates outward. Extreme cases may mimic acute appendicitis.
Diagnosis:
Children with hookworm release eggs that can be detected by direct fecal examination . Quantitative methods are available to determine whether a child has a heavy worm burden that can cause hookworm disease. The eggs of N. americanus and A. duodenale are morphologically indistinguishable.
Treatment:
The goal of deworming is removal of the adult hookworms with an anthelmintic drug. The benzimidazole anthelmintics, mebendazole and albendazole, are effective at eliminating hookworms from the intestine, although multiple doses are sometimes required. Albendazole (400 mg PO once, for all ages) usually achieves high cure rates, although N. americanus adult hookworms are sometimes more refractory and require additional doses. Mebendazole (100 mg bid PO for 3 days, for all ages) is also effective. In many developing countries, mebendazole is administered as a single dose of 500 mg; with this regimen the cure rates can be as low as 20–30%.
An infantile form of ancylostomiasis resulting from heavy A. duodenaleinfection has been described. Affected infants experience diarrhea, melena, failure to thrive, and profound anemia. Infantile ancylostomiasis has significant mortality.
Eosinophilic enteritis caused by A. caninum is associated with colicky abdominal pain, usually exacerbated by food, which begins in the epigastrium and radiates outward. Extreme cases may mimic acute appendicitis.
Diagnosis:
Children with hookworm release eggs that can be detected by direct fecal examination . Quantitative methods are available to determine whether a child has a heavy worm burden that can cause hookworm disease. The eggs of N. americanus and A. duodenale are morphologically indistinguishable.
Treatment:
The goal of deworming is removal of the adult hookworms with an anthelmintic drug. The benzimidazole anthelmintics, mebendazole and albendazole, are effective at eliminating hookworms from the intestine, although multiple doses are sometimes required. Albendazole (400 mg PO once, for all ages) usually achieves high cure rates, although N. americanus adult hookworms are sometimes more refractory and require additional doses. Mebendazole (100 mg bid PO for 3 days, for all ages) is also effective. In many developing countries, mebendazole is administered as a single dose of 500 mg; with this regimen the cure rates can be as low as 20–30%.
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