name = Necator americanus and Ancylostoma duodenale
subdivision_ranks = Species
subdivision = Species N. americanus and A. duodenale
The hookworm is a parasitic
nematodeworm that lives in the small intestineof its host, which may be a mammalsuch as a dog, cat, or human. Two speciesof hookworms commonly infect humans, "Ancylostoma duodenale" and "Necator americanus". "Necator americanus" predominates in the Americas, Sub-Saharan Africa, Southeast Asia, Chinaand Indonesia, while "A. duodenale" predominates in the Middle East, North Africa, Indiaand (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" and "Egyptian chlorosis", is the disease caused by hookworms. It is caused when hookworms, present in large numbers, produce an
iron deficiency anemiaby voraciously sucking blood from the host's intestinal walls. The name is derived from Greek ancylo "crooked, bent" and stoma "mouth."
Hookworm is a leading cause 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.
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.
Angelo Dubiniwas the modern-day discoverer of the worm in 1838 after an autopsyof 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 chlorosis, which would probably be called iron deficiency anemiatoday.
A breakthrough came 25 years later following a
diarrheaand anemiaepidemic that took place among Italian workmen employed on the Gotthard Rail Tunnel. In an 1880 paper, physicians Camillo Bozzolo, Edoardo Perroncito, and Luigi Paglianicorrectly hypothesized that hookworm was linked to the fact that workers had 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 biological life cycleof the hookworm was clarified. In 1899, American zoologist Charles Wardell Stilesbrought 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". Testing in the 1900s revealed very heavy infestations in schoolage children.
October 26, 1909the Rockefeller Sanitary Commission for the Eradication of Hookworm Disease was organized as a result of a gift of US$1 million from John D. Rockefeller, Sr. 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 and 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 Indiestowards the end of the 18th century, as well as through descriptions sent from Braziland various other tropical and sub-tropical regions.
Early treatment was with
thymolto kill the worms, followed by epsom saltto clear the body of the worms. Later on, tetrachloroethylenewas the leading method. It was not until later in the mid-20th century when new organic drug compounds were developed.
Most individuals with hookworm infection have no symptoms. Generally, very high loads of the parasite coupled with poor nutrition (inadequate intake of protein and iron) eventually lead to anemia.
The disease was linked to nematode worms ("Ankylostoma duodenalis") from one-third to half an inch long in the intestine chiefly through the labours of
Theodor Bilharzand Griesingerin Egypt (1854).
The symptoms can be linked to inflammation in the gut stimulated by feeding hookworms, such as nausea, abdominal pain and intermittent diarrhea, and to progressive anemia in prolonged disease: appetite, pica (or dirt-eating), obstinate constipation followed by
diarrhea, palpitations, thready pulse, coldness of the skin, pallor of the mucous membranes, fatigue and weakness, shortness of breath and in cases running a fatal course, dysentery, hemorrhagesand edema.
Blood tests in early infection often show a rise in numbers of eosinophils, a type of white blood cell that is preferentially stimulated by worm infections in tissues (large numbers of eosinophils are also present in the local inflammatory response). Falling blood hemoglobin levels will be seen in cases of prolonged infection with anemia.
In contrast to most intestinal
helminthiases, where the heaviest parasitic loads tend to occur in children, hookworm prevalence and intensity can be higher among adult males. The explanation for this is that hookworm infection tends to be occupational, so that plantation workers, coalminers and other groups maintain a high prevalence of infection among themselves by contaminating their work environment. However, in most endemic areas, adult women are the most severely affected by anemia, mainly because they have much higher physiological needs for iron (menstruation, repeated pregnancy), but also because customarily they have access to much poorer food than the men.
An interesting consequence of this in the case of "Ancylostoma duodenale" infection is translactational transmission of infection: the skin-invasive larvae of this species do not all immediately pass through the lungs and on into the gut, but spread around the body via the circulation, to become dormant inside muscle fibers. In a pregnant woman, after childbirth some or all of these larvae are stimulated to re-enter the circulation (presumably by sudden hormonal changes), then to pass into the mammary glands, so that the newborn baby can receive a large dose of infective larvae through its mother's milk. This accounts for otherwise inexplicable cases of very heavy, even fatal, hookworm infections in children a month or so of age, in places such as China, India and northern Australia. (An identical phenomenon is much more commonly seen with "Ancylostoma caninum" infections in dogs, where the newborn pups can even die of hemorrhaging from their intestines caused by massive numbers of feeding hookworms. This also reflects the close evolutionary link between the human and canine parasites, which probably have a common ancestor dating back to when humans and dogs first started living closely together.)
Hookworm in therapy
Moderate hookworm infections have been demonstrated to have beneficial effects on hosts suffering from diseases linked to overactive immune systems. This is possibly explained by the
hygiene hypothesis.cite journal |author= Strachan D P. |title= Hay fever, hygiene, and household size |journal= BMJ. |volume=18 |issue=299 |pages=1259–60 |year=2006 |pmid=2513902 |pmc=1838109|doi=] Research at the University of Nottinghamconducted in Ethiopia has demonstrated that people with hookworm infections are half as likely to experience asthma[BBC Health [http://news.bbc.co.uk/1/hi/health/1632863.stm Worm infestation 'beats asthma'] ] or hay fever. [BBC Health [http://news.bbc.co.uk/2/hi/health/3287733.stm Eat worms - feel better] ] It may also help sufferers of multiple sclerosis, [cite journal |author=Correale J, Farez M |title=Association between parasite infection and immune responses in multiple sclerosis |journal=Ann. Neurol. |volume=61 |issue=2 |pages=97–108 |year=2007 |month=February |pmid=17230481 |doi=10.1002/ana.21067 ] Crohn's Disease[cite journal |author=Croese J, O'neil J, Masson J, "et al" |title=A proof of concept study establishing Necator americanus in Crohn's patients and reservoir donors |journal=Gut |volume=55 |issue=1 |pages=136–7 |year=2006 |month=January |pmid=16344586 |doi=10.1136/gut.2005.079129 |url=http://gut.bmj.com/cgi/pmidlookup?view=long&pmid=16344586] and diabetes.Daily Mail. [http://www.dailymail.co.uk/pages/live/articles/technology/technology.html?in_article_id=481875&in_page_id=1965 The bloodsucking worm that fights allergies from inside your tummy] September 14 2007.]
Hookworm therapy to treat a number of these diseases is currently in the trial stage at the University. Some people, including Dr. David Pritchard of the University of Nottingham, and Jasper Lawrence of Autoimmune Therapies, have independently infected themselves with hookworms and reported positive results. [ [http://www.nytimes.com/2008/07/01/health/research/01prof.html?pagewanted=1&_r=1&sq&st=nyt&scp=2 The Worms Crawl In - The New York Times] .
May 1, 2006.]
See the image for the
biological life cycleof the hookworms where it thrives in warm earth where temperatures are over 18°C. They exist primarily in sandy or loamy soil and cannot live in clayor muck. Rainfallaverages must be more than 1000 mm (40 inches) a year. Only if these conditions exist can the eggs hatch. Infective larvae of "Necator americanus" can survive at higher temperatures, whereas those of "Ancylostoma duodenale" are better adapted to cooler climates. Generally, they live for only a few weeks at most under natural conditions, and die almost immediately on exposure to direct sunlight or desiccation.
Infection of the host is by the larvae, not the eggs. While "A. duodenale" can be ingested, the usual method of infection is through the skin; this is commonly caused by walking barefoot through areas contaminated with fecal matter. The larvae are able to penetrate the skin of the foot, and once inside the body, they migrate through the
vascular systemto the lungs, and from there up the trachea, and are swallowed. They then pass down the esophagusand enter the digestive system, finishing their journey in the intestine, where the larvae mature into adult worms. [ [http://www.cdc.gov/ncidod/dpd/parasites/hookworm/factsht_hookworm.htm "CDC Factsheet: Hookworm"] , accessed September 29, 2008] [Peter J Hotez, Jeff Bethony, Maria Elena Bottazzi, Simon Brooker, and Paulo Buss, [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1069663 "Hookworm: the Great Infection of Mankind"] , PLoS Med. 2005 March; 2(3): e67.]
Once in the host gut, "Necator" tends to cause a prolonged infection, generally 1–5 years (many die within a year or two of infecting), though some adult worms have been recorded to live for 15 years or more. On the other hand, "Ancylostoma" adults are short lived, surviving on average for only about 6 months. However, infection can be prolonged because dormant larvae can be "recruited" sequentially from tissue "stores" (see Pathology, above) over many years, to replace expired adult worms. This can give rise to seasonal fluctuations in infection prevalence and intensity (apart from normal seasonal variations in transmission).
They mate inside the host, females laying up to 30,000 eggs per day, which pass out in feces. Because it takes 5–7 weeks for adult worms to mature, mate and produce eggs, in the early stages of very heavy infection, acute symptoms might occur without any eggs being detected in the patient's feces. This can make diagnosis very difficult.
The infective larvae develop and survive in an environment of damp dirt, particularly sandy and loamy soil. They cannot survive in clay or muck. The main lines of precaution are those dictated by sanitary science:
*Do not defecate outside latrines, toilets etc.
*Do not use human excrement or raw
sewageas manure/fertilizer in agriculture
*Deworm pet dogs — canine and feline hookworms rarely develop to adulthood in humans ("Ancylostoma caninum", the common dog hookworm, occasionally develops into an adult to cause eosinophilic enteritis in people), but their invasive larvae can cause an itchy rash called
cutaneous larva migrans. Moxidectinhas been released in the United States as part of Advantage Multi (imidacloprid + moxidectin) Topical Solution for dogs and cats. It utilizes moxidectin for control and prevention of roundworms, hookworms, heartworms, and whipworms.
In the late 1800s and early 1900s, many
Mississippianswere plagued by hookworms. They did not have indoor plumbingor proper sanitation facilities. As a result, hookworms, spread by fecal contamination of the environment, were very prevalent (as well as other diseases caused by lack of sanitation).
There are no specific symptoms or signs of hookworm infection. As mentioned above, they arise from a combination of intestinal inflammation and progressive iron/protein-deficiency anemia. Larval invasion of the skin might give rise to intense, local itching, usually on the foot or lower leg, which can be followed by lesions that look like insect bites, can blister ("ground itch"), and last for a week or more. Coughing, chest pain, wheezing, and fever will sometimes be experienced by people who have been exposed to very large numbers of larvae. Epigastric pains, indigestion, nausea
vomiting, constipation, and diarrheacan occur early or in later stages as well, although gastrointestional symptoms tend to improve with time. Signs of advanced severe infection are those of anemia and protein deficiency, including emaciation, cardiac failure and abdominal distension with ascites.
Diagnosis depends on finding characteristic worm eggs on microscopic examination of the stools, although this is not possible in early infection. As the eggs of both "Ancylostoma" and "Necator" (and most other hookworm species) are indistinguishable, to identify the genus, they must be cultured in the lab to allow larvae to hatch out. If the fecal sample is left for a day or more under tropical conditions, the larvae will have hatched out, so eggs might no longer be evident. In such a case, it is essential to distinguish hookworms from "Strongyloides" larvae, as infection with the latter has more serious implications and requires different management. The larvae of the two hookworm species can also be distinguished microscopically, although this would not be done routinely, but usually for research purposes. Adult worms are rarely seen (except via endoscopy, surgery or autopsy), but if found, would allow definitive identification of the species.
The hookworm can be treated with local
cryotherapywhen it is still in the skin. Albendazoleis effective both in the intestinal stage and during the stage the parasite is still migrating under the skin.
In case of anemia,
ironsupplementation can cause relief symptoms of iron deficiency anemia. However, as red blood cell levels are restored, shortage of other essentials such as folic acidor vitamin B12may develop, so this might also be supplemented.
Cutaneous larva migrans(creeping eruption)
List of parasites (human)
* [http://www.dpd.cdc.gov/dpdx/HTML/ImageLibrary/Hookworm_il.htm CDC Department of Parasitic Diseases images of the hookworm life cycle]
* [http://www.cdc.gov/ncidod/dpd/parasites/hookworm/factsht_hookworm.htm Centers for Disease Control and Prevention]
* [http://www.sabin.org/programs/hhvi Human Hookworm Vaccine Initiative]
* [http://archive.rockefeller.edu/feature/hookworm.php The Rockefeller University]
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Look at other dictionaries:
hookworm — ► NOUN ▪ a parasitic worm which inhabits the intestines and feeds by attaching itself with hook like mouthparts … English terms dictionary
hookworm — ☆ hookworm [hook′wʉrm΄ ] n. any of a superfamily (Ancylostomatoidea) of small, parasitic, intestinal nematode worms with hooks around the mouth: found esp. in tropical climates … English World dictionary
Hookworm — An intestinal parasite that usually causes diarrhea or cramps. Heavy infestation with hookworm can be serious for newborns, children, pregnant women, and persons who are malnourished. Hookworm infections occur mainly in tropical and subtropical… … Medical dictionary
hookworm — UK [ˈhʊkˌwɜː(r)m] / US [ˈhʊkˌwɜrm] noun Word forms hookworm : singular hookworm plural hookworms 1) [countable] a long thin creature that lives in the intestines of humans and other animals, and that can cause disease 2) [uncountable] the disease … English dictionary
hookworm — hookwormy, adj. /hook werrm /, n. 1. any of certain bloodsucking nematode worms, as Ancylostoma duodenale and Necator americanus, parasitic in the intestine of humans and other animals. 2. Also called hookworm disease. a disease caused by… … Universalium
hookworm — n. either of two nematode worms, Necator americanus or Ancylostoma duodenale, which live as parasites in the human intestine. Both species, also known as the New and Old World hookworms respectively, are of great medical importance (see hookworm… … The new mediacal dictionary
hookworm — /ˈhʊkwɜm / (say hookwerm) noun 1. any of certain bloodsucking nematode worms, as Ancylostoma duodenale and Necator americanus, parasitic in the intestine of humans and other animals. 2. → hookworm disease … Australian English dictionary
hookworm — noun Date: 1902 1. any of several parasitic nematode worms (family Ancylostomatidae) that have strong buccal hooks or plates for attaching to the host s intestinal lining and that include serious bloodsucking pests 2. infestation with or disease… … New Collegiate Dictionary
hookworm — noun Any of various parasitic bloodsucking roundworms which cause disease, especially the species Ancylostoma duodenale and Necator americanus. They have hooked mouthparts and enter their hosts by boring through the skin … Wiktionary
hookworm — Synonyms and related words: African lethargy, Asiatic cholera, Chagres fever, German measles, Haverhill fever, acute articular rheumatism, ague, alkali disease, amebiasis, amebic dysentery, anthrax, bacillary dysentery, bastard measles, black… … Moby Thesaurus