The hookworm is a nematode parasite that lives in the small intestine of its host, which may be a mammal such as a dog, cat, or human. Two species of hookworms commonly infect humans, Ancylostoma duodenale and Necator americanus. The geographical distribution of these two species significantly overlap. Necator americanus predominates in the Americas, Sub-Saharan Africa, Southeast Asia, China and Indonesia, while A. duodenale predominates in the Middle East, North Africa, India and (formerly) in southern Europe. Hookworms are thought to infect 800 million people worldwide. The A. braziliense and A. tubaeforme species infect cats, while A. caninum infects dogs. Uncinaria stenocephala infects both dogs and cats.

Hookworms are much smaller than the large roundworm, Ascaris lumbricoides, and the complications of tissue migration and mechanical obstruction so frequently observed with roundworm infestation are less frequent in hookworm infestation. The most significant risk of hookworm infection is anemia, secondary to loss of iron (and protein) in the gut. The worms suck blood voraciously and damage the mucosa. However, the blood loss in the stools is occult blood loss (not visibly apparent).

Ankylostomiasis, alternatively spelled anchylostomiasis and also called helminthiasis, "miners' anaemia", "tunnel disease", "brickmaker's anaemia", "Egyptian chlorosis" and in Germany Wurmkrankheit, is the disease caused by hookworms. It is caused when hookworms are present in large numbers and produce a severe anaemia by voraciously sucking blood from the host's intestinal walls.

Hookworm is commonly called "larva migratoria" in Spanish and "bicho do pé" in Portuguese.

Hookworms are leading causes of maternal and child morbidity in the developing countries of the tropics and subtropics. In susceptible children hookworms cause intellectual, cognitive and growth retardation, intrauterine growth retardation, prematurity, and low birth weight among newborns born to infected mothers. Hookworm infection is rarely fatal, but anemia can be significant in the heavily infected individual.

History

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The symptoms now attributed to hookworm appear in papyrus papers of ancient Egypt (c. 1600 B.C.), described as a derangement characterized by anemia. Avicenna, a Persian physician of the 11th century, discovered the worm in several of his patients and related it to their disease. In later times, the condition was noticeably prevalent in the mining industry in England, France, Germany, Belgium, North Queensland and elsewhere.

Italian physician Angelo Dubini was the modern-day discoverer of the worm in 1838 after an autopsy of a peasant woman. Dubini published details in 1843 and identified the species as A. duodenale. Working in the Egyptian medical system in 1852 German physician Theodor Bilharz, drawing upon the work of colleague Wilhelm Griesinger, found these worms during autopsies and went a step further in linking them to local endemic occurrences of anemia and chlorosis.

A breakthrough came 25 years later following a diarrhea and anemia epidemic that took place among Italian workmen employed on the Gotthard Rail Tunnel. In an 1880 paper, physicians Camillo Bozzolo, Edoardo Perroncito, and Luigi Pagliani correctly hypothesized that hookworm was linked to the fact that workers were forced to defecate inside the 15 km tunnel, and that many wore worn-out shoes. In 1897, it was established that the skin was the principal avenue of infection and the life cycle of the hookworm was clarified. In 1899, American zoologist Charles Stiles brought this evidence to bear on health issues in the southeast United States, identifying "progressive pernicious anemia" seen in the southern United States was caused by A. duodenale and he also identified the other important hookworm species: U. Necator. Indeed, testing in the 1900s revealed very heavy infestations in schoolage children.

In October 1909 the Rockefeller Sanitary Commission for the Eradication of Hookworm Disease was organized on October 26, 1909 as a result of a gift of $1 million from John D. Rockefeller, Sr. Though humanitarian reasons are cited, some speculate that the motive was to open markets in the Appalachian region by creating more disposable income. Nevertheless the five-year program was a remarkable success and a great contribution to United States public health, instilling public education, medication, field work, and modern government health departments in eleven southern states. The hookworm exhibit was a prominent part of the 1910 Mississippi state fair. The program nearly eradicated hookworm. The program would flourish afterwards with new funding as the Rockefeller Foundation International Health Division.

In the 1920s, hookworm eradication reached the Caribbean and Latin America, where great mortality was reported among blacks in the West Indies towards the end of the 18th century, as well as through descriptions sent from Brazil and various other tropical and sub-tropical regions.

Early treatment was with thymol to kill the worms, followed by epsom salt to clear the body of the worms. Later on, tetrachloroethylene was the leading method. It wasn't until later in the mid-20th century when new organic drug compounds were developed.

Pathology

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Most individuals with hookworm infection are asymptomatic (without symptoms). Only very high loads of the parasite or poor nutrition combined with infection lead to anemia.

The disease was linked to nematoid worms (Ankylostoma duodenalis) from one-third to half an inch long in the intestine chiefly through the labours of Theodor Bilharz and Griesinger in Egypt (1854).

The symptoms, as first observed among blacks, were pain in the stomach, capricious appetite, pica (or dirt-eating), obstinate constipation followed by diarrhea, palpitations, small and unsteady pulse, coldness of the skin, pallor of the skin and mucous membranes, diminution of the secretions, loss of strength and, in cases running a fatal course, dysentery, haemorrhages and oedema.

In contrast with most intestinal helminthiases that concentrate parasitic load in children, hookworm prevalence is often higher among adult males. In tropical areas this is associated with high prevalence of anemia among adult men.

Hookworm in therapy

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Moderate hookworm infections have been demonstrated to have beneficial effects on their hosts. Research at the University of Nottingham conducted in Ethiopia has demonstrated that people with hookworm infections are half as likely to experience asthmaBBC Health Worm infestation 'beats asthma' or hay fever.BBC Health Eat worms - feel better

The theory is that our immune systems evolved under constant assault from a variety of parasites, most of which have to modulate our immune response to succeed. That is, they have to down regulate the response that would otherwise attack them. Evolving with a down-regulated immune system means that in the absence of those down-regulating parasites our immune systems often attack our own tissues, leading to asthma, hay fever, IBD, colitis, Crohn's and perhaps other autoimmune diseases. Hence the increase in autoimmune diseases in the relatively clean and sterile industrialized world.

Life cycle

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See the image for the biological life cycle of the hookworm.

The hookworm larva lives in infected soil, particularly in tropical climates and coal mines where it thrives in warm earth where temperatures are over 18°C. They exist primarily in sandy or loamy soil, and cannot live in clay or muck. Rainfall averages must be more than 40 inches a year. Only if these conditions exist can the eggs hatch.

The larva penetrates the skin on contact, for example when walking barefoot, enters the bloodstream and is transported to the lungs. From the lungs and bronchi it transfers to the stomach and intestine by coughing up and swallowing phlegm. This causes little Löffler symptoms. The larva clings to the intestinal mucous membrane and develops into an adult hookworm, drawing its nourishment from the blood-vessels of their host, and as the parasites are found in hundreds in the body after death, the disorders of digestion, the increasing anaemia and the consequent oedema and other cachectic symptoms are easily explained. The adult releases eggs that leave the host body with the feces. The eggs rapidly (within 24 hours) hatch in soil and eventually develop into larva, which is contagious after one week and stays contagious for several weeks.

It's possible that the worm doesn't immediately produce eggs, but does cause anemia. Diagnosis is more difficult during this latent stage.

Prevention

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The parasites thrive in an environment of dirt, particularly sandy and loamy soil. They cannot exist in clay or muck. The main lines of precaution are those dictated by sanitary science:

• Prevent skin/soil contact: do not walk barefoot
• Do not defecate outside latrines, toilets etc.
• Do not use human excrement or raw sewage as manure/fertilizer in agriculture
• Worm pet dogs (canine hookworms cannot develop to adulthood in humans, but can cause an unpleasant rash called cutaneous larva migrans).

In the late 1800s and early 1900s, many Mississippians were plagued by hookworms. They did not have indoor plumbing or proper sanitation facilities. As a result, hookworms from feces and other sources were very prevalent (as well as other diseases caused by lack of sanitation).

Diagnosis

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To infected persons who have walked outside in soil infested with hookworms, mosquito-like "bites" on the sole of the foot may indicate hookworm entry. They also commonly appear on the hands if the person has been handling dirt. On the second day the "bites" turn into lines and medical attention is advised.

People infected with hookworms often experience low energy. Coughing, wheezing, and fever will develop in the victim sometimes as the larva travel to the lungs. Stomach pains, yellow skin, feet that go to sleep, head and joint aches, weakness, vomiting, constipation, and diarrhoea are other common symptoms. Very common visible symptoms include a pot belly and angel's wings - shoulder blades that are extended forward, because of the person's slumped, emaciated body. In severe cases, blurred vision and a fish-eye stare have been reported.

The mainstay of diagnosis is to detect the worm eggs on microscopal examination of the stools, but this may not be possible when the worm does not immediately produce eggs.

Sometimes larvae can be seen in an older feces sample on room temperature.

Treatment

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Hookworm can be treated with local cryotherapy when it is still in the skin.

Albendazole is effective both in the intestinal stage and during the stage the parasite is still migrating under the skin.

In case of anemia, iron supplementation can cause relief symptoms of iron deficiency anemia. However, as red blood cell levels are restored, shortage of other essentials such as folic acid or vitamin B12 may develop, so this might also be supplemented.

See also

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• Creeping eruption

Notes

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References

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External links

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• CDC Department of Parasitic Diseases images of the hookworm life cycle
• http://www.cdc.gov/ncidod/dpd/parasites/hookworm/factsht_hookworm.htm
• Personal MD, more hookworm info
• http://archive.rockefeller.edu/feature/hookworm.php
• http://mshistory.k12.ms.us/features/feature31/hookworm.html
• http://www.thelifetree.com/hookworms.htm
• http://www.asthmahookworm.com
• http://www.wellcome.ac.uk/doc_WTX026496.html

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