The human hookworm Necator americanus is a roundworm native to tropical and temperate regions.
According the World Health Organisation an estimated 740 million people worldwide are currently carrying hookworms, mainly in sub-Saharan Africa, Latin America, South-East Asia and China. This makes it the second most common human helminth (after ascaris lumbricoides).
Necator americanus is considered to be an ideal worm for Helminthc Treatment because it is asymptomatic in small numbers, it cannot be spread directly from one person to another, it consumes only a small amount of blood from its host, and it is long living so need for re-dosing is less frequent.
Adult Necator americanus worms are approximately 1cm long and the width of a human hair. They reside in the small intestine where they attach to the intestinal wall and feed from the blood of their host.
An adult worm is capable of ingesting 0.03ml of blood per day. The main health problem associated with hookworms is iron deficiency anaemia due to blood loss but this can only occur in hosts with a very large number of worms. A person with a small number of worms will usually be asymptomatic beyond the initial signs of colonization (skin rash and possible short term respiratory and abdominal symptoms during migration and maturation of larvae), and it is recommended by the US Center for Disease Control that healthcare professionals need not treat small numbers of hookworms, such as those used in Helminthic Treatment.
The life cycle of Necator americanus begins with unembryonated eggs being passed in the host’s stool. The eggs require moist, warm, shaded and sandy soil conditions, and only in this environment will larvae develop and hatch within 2 to 3 days. The larvae then molt twice within the next 10 days to become infective. When infective larvae make contact with human skin they will penetrate it and travel through the circulatory system to the lungs. The larvae then migrate into the throat where they are swallowed into the stomach and pass into the small intestine. Here they molt twice more to become adult worms. The adult worms reside in the lumen of the small intestine where they attach to the inner wall and feed from the blood of the host. Adult females will begin to produce eggs which are deposited in stool and thus the cycle continues.
The migration and maturation of Necator americanus larvae takes approximately 6 to 8 weeks. During this time it is possible for hosts to experience some temporary side effects such as an itchy rash at the point of entry, a cough during the migration through the lungs, and abdominal cramping, diarrhea and fatigue during maturation in the intestine. With a small dose, as used in Helminthic Treatment, many will not experience any side effects at all.
The lifespan of an adult worm is typically around 2 to 5 years.
A hookworm colony can be easily eradicated with a short course of antihelminthic drugs (Albendazole or Mebendazole).
Hookworms have become very rare in developed countries due to modern sewerage systems. Because all eggs are immediately flushed away they never experience the environmental conditions needed to hatch and become infective. This makes it impossible to pass hookworms directly from one person to another anywhere with modern sanitation.