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Note: description of Ancylostoma caninum (dog hookworm) can be found here.
- Ancylostoma duodenale taxonomy
- Necator americanus taxonomy
- Brief facts
- Developmental stages
In 1962, Norman Stoll, the distinguished Rockefeller Institute scientist who helped to establish human parasitology research in North America, described the health impact of hookworm:As it was when I first saw it, so it is now, one of the most evil of infections. Not with dramatic pathology as are filariasis, or schistosomiasis, but with damage silent and insidious. Now that malaria is being pushed back hookworm remains the great infection of mankind. In my view it outranks all other worm infections of man combined…in its production, frequently unrealized, of human misery, debility, and inefficiency in the tropics.
cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Pseudocoelomata - Nematoda - Chromadorea - Rhabditida - Strongylida - Ancylostomatoidea - Ancylostomatidae - Ancylostomatinae - Ancylostoma - Ancylostoma duodenale
cellular organisms - Eukaryota - Fungi/Metazoa group - Metazoa - Eumetazoa - Bilateria - Pseudocoelomata - Nematoda - Chromadorea - Rhabditida - Strongylida - Ancylostomatoidea - Ancylostomatidae - Bunostominae - Necator - Necator americanus
- Together with human roundworms (see Ascaris lumbricoides at MetaPathogen) and whipworms (Trichuris trichiura), hookworms belong to a group of so-called soil-transmitted helminths that represent one of the world's most important causes of physical and intellectual growth retardation.
- Hookworm infection in humans is usually caused by one of two species of nematodes (roundworms) - Necator americanus or Ancylostoma duodenale. N. americanus is most common human-specific hookworm worldwide, distribution of A. duodenale is geographically more restricted. Both N. americanus and A. duodenale are found in Africa, Asia and the Americas. Necator americanus predominates in the Americas and Australia, while only A. duodenale is found in the Middle East, North Africa and southern Europe.
- Today, hookworm infection is among the most important tropical diseases in humans with more than 750 million infected people world-wide.
- Hookworm infection is the second most common human helminthic infection (after ascariasis).
- The species give similar clinical manifestations of the infection, although A. duodenale can lead to a greater blood loss and anemia.
- Infection with N. americanus can occur only through skin penetration by L3 larvae. A. duodenale can infect humans upon swallowing of the larvae.
- The major clinical symptom of the hookworm infection is iron-deficiency anemia accompanied by other physical signs such as sickly yelowish color of the skin, hypothermia, eosinophilia (high concentration of eosinophils in the blood), abdominal pain, fatigue, and impotence. Children may suffer from stunted growth and mental retardation.
- Intensity and probability of many common helminthic infections, including ascariasis, trichuriasis, and schistosomiasis, usually peak during childhood and adolescence. In contrast, occurence of the hookworm infection grows with age, with highest intensity in middle-aged persons, or even older.
- Usually the hookworm infection is treated with a single dose of a benzimidazole antihelminthic, such as albendazole or mebendazole. There were troubling reports that the parasites gradually acquire resistance to these drugs.
- Soil-transmitted helminths do not reproduce within the host: in order to be infective their eggs have to be released into environment where they are embryonated (roundworms, whipworms) or hatch into infective larvae (hookworms). Usually the eggs as well as the larvae do not enter the same host, who released them. This feature is crucial for understanding of the epidemiology and methods of control (compare with pinworm, Enterobius vermicularis, (pinworm) at MetaPathogen).
The life cycles of hookworms species are similar. Parasites are dioecious, with male and female organs in separate individuals. They mate in host's small intestine and the females produce eggs. Following copulation, female lays her eggs.
- egg usual daily output of eggs for single female hookworm is between 10,000 and 30,000 eggs; eggs are passed to the environment with feces
- rhabditiform larva
larva 1 (L1) rhabditiform larvae hatch from eggs in a warm soil (~48 hours); it feeds on bacteria and other microorganisms
larva 2 (L2) rhabditiform larvae first stage molt to rhabditiform larvae second stage by third day
- filariform larva (L3) rhabditiform larva second stage molts to filariform larva (L3); this is infectious non-feeding stage of the hookworm; the larvae migrate to the grass blades and "stand up" on their tails ready to stick to the passing host; the larvae survive for several week without feeding until they exaust their metabolic reserves; they adhere to the host on contact and penetrate skin causing so-called "ground itch"
- immature adult swept by blood stream L3 larvae in about 10 days after entry reach the heart and then, lungs, where they rupture capillaries and ascend the alveoli, bronchioles, bronchi, and trachea; the host coughs up the larvae and swallows them; when the larvae reach the small intestine, they settle, start feeding, and undergo two additional moltings
- mature adult after 2 moltings the parasites mature into adults and mate; intestinal blood loss begins just before egg production and continues for the life of the worm (up to 5 years); to ensure blood flow, adults release anticlotting agents (the agents were isolated and applied in therapeutics to block blood coagulation in several diseases); adult females: 10 to 13 mm (A. duodenale), 9 to 11 mm (N. americanus); adult males: 8 to 11 mm (A. duodenale), 7 to 9 mm (N. americanus)
Brindley PJ, Mitreva M, Ghedin E, Lustigman S. Helminth genomics: The implications for human health. PLoS Negl Trop Dis. 2009 Oct 26;3(10):e538.
Hookworm egg passed in the stool of an infected person; the microscopic egg, barrel-shaped with a thin wall, is about 70×40 µm in dimension.
Longitudinal section through an adult hookworm attached to wall of small intestine, ingesting host blood and mucosal wall. The parasite is about 1 cm in length.
Archer M. Late presentation of cutaneous larva migrans: a case report. Cases J. 2009 Aug 12;2:7553.
Photograph of right foot taken on date of presentation showing typical serpiginous lesion of cutaneous larva migrans.
Vano-Galvan S, Gil-Mosquera M, Truchuelo M, Jaén P. Cutaneous larva migrans: a case report. Cases J. 2009 Jan 31;2(1):112.
Dermatological examination showed an erythematous serpiginous intraepidermal tunnel on his left leg, caused by accidental percutaneous penetration of the larva.
Hotez PJ, Bethony J, Bottazzi ME, Brooker S, Buss P. Hookworm: "the great infection of mankind".
PLoS Med. 2005 Mar;2(3):e67.
Global Distribution of Human Hookworm Infection.
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- Hawdon JM, Hotez PJ. Hookworm: developmental biology of the infectious process. Curr Opin Genet Dev. 1996 Oct;6(5):618-23.