Hookworm

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Ancylostoma caninum hookworms in a dog Hookworms.JPG
Ancylostoma caninum hookworms in a dog

Hookworms are intestinal, blood-feeding, parasitic roundworms that cause types of infection known as helminthiases. Hookworm infection is found in many parts of the world, [1] and is common in areas with poor access to adequate water, sanitation, and hygiene. In humans, infections are caused by two main species of roundworm, belonging to the genera Ancylostoma and Necator . In other animals the main parasites are species of Ancylostoma. Hookworm is closely associated with poverty because it is most often found in impoverished areas, and its symptoms promote poverty through the educational and health effects it has on children. [2] It is the leading cause of anemia and undernutrition in developing countries, while being one of the most commonly occurring diseases among poor people. Hookworm thrives in areas where rainfall is sufficient and keeps the soil from drying out, and where temperatures are higher, making rural, coastal areas prime conditions for the parasite to breed.

Contents

Species

Infective N. americanus larva Necator Americanus L3 x1000 12-2007.jpg
Infective N. americanus larva

The two most common types of hookworm that infect humans are Ancylostoma duodenale and Necator americanus .[ citation needed ]

Hookworm species that are known to infect domestic cats are Ancylostoma braziliense and Ancylostoma tubaeforme . Wild cats are infected by Ancylostoma pluridentatum . [3]

Dogs are commonly infected by Ancylostoma caninum , but may also be infected by Uncinaria stenocephala and Ancylostoma braziliense.[ citation needed ]

In Asia, Ancylostoma ceylanicum is endemic among dogs and cats and infects humans. [4]

Cattle are infected by Bunostomum phlebotomum. [1]

At least 68 species have been described in wild mammals. [5]

Characteristics

The two species that commonly infect humans have a similar morphology. A. duodenale worms are pale grey or slightly pink. The head is bent a little in relation to the rest of the body, forming a hook shape – hence the name. The hook is at the front end of the body. They have well-developed mouths with two pairs of teeth. Males measure approximately 10 by 0.5 mm, and females are often longer and stouter. Males also have a prominent copulatory bursa posteriorly. [6]

N. americanus is generally smaller than A. duodenale, with males usually being 5 to 9 mm long and females about 10 mm long. Instead of the two pairs of teeth in A. duodenale, N. americanus has a pair of cutting plates in the buccal capsule. Also, the hook is much more defined in Necator americanus. [6]

Life cycle

Hookworm life cycle Hookworm LifeCycle.gif
Hookworm life cycle

The host is infected by the larvae, not by the eggs, and the usual route is through the skin. Hookworm larvae need warm, moist soil, above 18 °C, in order to hatch. They will die if exposed to direct sunlight or if they become dried out. Necator larvae can survive at higher temperatures than Ancylostoma larvae. [ citation needed ]

First-stage larvae (L1) are non-infective, and once hatched in the deposited feces, they feed on that, and then feed on soil microorganisms until they moult into second stage larvae (L2). [7] First- and second-stage larvae are in the rhabditiform stage. After feeding for seven days or so they will moult into third-stage larvae (L3) known as the filariform stage, which is the non-feeding, infective stage. Filariform larvae can survive for up to two weeks. They are extremely motile and will move onto higher ground to improve their chances of finding a host.[ citation needed ]

Necator americanus larvae can only infect through penetrating skin, but A. duodenale can also infect orally. A common route of passage for the larvae is the skin of barefoot walkers. Once the larvae have entered the host they travel in the circulatory system to the lungs where they leave the venules and enter the alveoli. They then travel up the trachea and are coughed up, swallowed and end up in the small intestine. In the small intestine, the larvae moult into stage four (L4) the adult worm. It takes from five to nine weeks from penetration to maturity in the intestine. [8] [9]

Necator americanus can cause a prolonged infection lasting from one to five years with many worms dying in the first year or two. Some worms though have been recorded as living for fifteen years or more. In comparison, Ancyclostoma duodenale worms are short-lived lasting for around six months. However, larvae can remain dormant in tissue stores and be recruited over many years to replace the worms that die.

The worms mate inside the host, in which the females also lay their eggs, to be passed out in the host's feces into the environment to start the cycle again. N. americanus can lay between nine and ten thousand eggs per day, and A. duodenale between twenty-five and thirty thousand per day. The eggs of the two species are indistinguishable.

Worms need five to seven weeks to reach maturity and symptoms of infection can therefore appear before eggs are to be found in the feces, making the diagnosis of hookworm infection difficult.

Diagnosis

Signs and symptoms of hookworm infection vary by host and hookworm species. In humans, the first sign of infection is itching and skin rash. Humans with light infections may show no symptoms, but humans with heavy infections may have abdominal pain, diarrhea, loss of appetite, weight loss, fatigue and anemia. Children's physical and cognitive growth may be affected. [10] [11] [12]

Dogs and cats may experience dermatitis, enteritis, and intestinal blood loss. Dogs may additionally experience anemia, hemorrhagic diarrhea, anorexia and dehydration. [1]

Cattle may experience skin lesions, anemia, and rapid weight loss. [1]

Diagnosis for many forms of hookworm infections is confirmed through fecal analysis to identify hookworm eggs. [10] In animals, fecal floatation is used to detect hookworm eggs. [1]

Treatment

Treatment for hookworm infections depends on the species of hookworm and the species of the infected host. In humans, treatment is by anthelminthic medications, such as albendazole and mebendazole. [13] Treatment in animals can be done with a variety of anthelminthics. [1] A high-protein diet, supplemental iron, or a blood transfusion may also be necessary. [1] Levamisole and pyrantel pamoate are also used to treat hookworm anemia and hookworm disease.

Prevention

Humans can avoid hookworm infections by avoiding skin-to-soil contact, such as walking barefoot, in areas where hookworms are common. Additionally, infection can be controlled by defecating indoors and not using human feces as a plant fertilizer. [10] Lawns and kennels may be sterilized by sodium borate. [1] Large education efforts funded by John D. Rockefeller helped reduce the rates of infection among children in the American South during the 1910s. [11]

Hookworm in the United States

While thought to be eradicated around the 1960s, Hookworm can still be found in certain areas in the United States. Lowndes County, Alabama was a subject of various studies on the prevalence and transmission of hookworm as it relates to sanitation issues that the county experienced. Catherine Coleman Flowers is the figure most closely associated with these studies and efforts to raise awareness of the sanitation problems that face Lowndes. Being one of the poorest counties in the United States with 31.4% of people living below the poverty line, [14] one of the major sanitation issues facing the county is that many residents do not have an adequate sewage system. The study led by The Baylor College of Medicine noted that roughly three-fourths of the study participants had reported raw sewage flowing back into their homes, increasing the likelihood of their home becoming contaminated. [15] The study in Lowndes had a small sample size of 55 subjects, from 24 households. The results from the screening of Hookworm found that over one-third, 19 out of 55 people testing positive, demonstrating a stronger correlation to poverty than to the tropics. [16] An important organization involved is The Alabama Center for Rural Enterprise (ACRE), which works to address poverty and economic development, and has stated that there continues to be a lack of adequate sewage systems, and this increases exposure to open sewage. [14] Surveys conducted before the testing reported that the subjects had not traveled abroad, making the infection site Alabama.

Related Research Articles

<span class="mw-page-title-main">Trichuriasis</span> Infection by Trichuris trichiura (whipworm)

Trichuriasis, also known as whipworm infection, is an infection by the parasitic worm Trichuris trichiura (whipworm). If infection is only with a few worms, there are often no symptoms. In those who are infected with many worms, there may be abdominal pain, fatigue and diarrhea. The diarrhea sometimes contains blood. Infections in children may cause poor intellectual and physical development. Low red blood cell levels may occur due to loss of blood.

<span class="mw-page-title-main">Helminthiasis</span> Any macroparasitic disease caused by helminths

Helminthiasis, also known as worm infection, is any macroparasitic disease of humans and other animals in which a part of the body is infected with parasitic worms, known as helminths. There are numerous species of these parasites, which are broadly classified into tapeworms, flukes, and roundworms. They often live in the gastrointestinal tract of their hosts, but they may also burrow into other organs, where they induce physiological damage.

<span class="mw-page-title-main">Hookworm infection</span> Disease caused by intestinal parasites

Hookworm infection is an infection by a type of intestinal parasite known as a hookworm. Initially, itching and a rash may occur at the site of infection. Those only affected by a few worms may show no symptoms. Those infected by many worms may experience abdominal pain, diarrhea, weight loss, and tiredness. The mental and physical development of children may be affected. Anemia may result.

<i>Necator americanus</i> Species of hookworm

Necator americanus is a species of hookworm commonly known as the New World hookworm. Like other hookworms, it is a member of the phylum Nematoda. It is an obligatory parasitic nematode that lives in the small intestine of human hosts. Necatoriasis—a type of helminthiasis—is the term for the condition of being host to an infestation of a species of Necator. Since N. americanus and Ancylostoma duodenale are the two species of hookworms that most commonly infest humans, they are usually dealt with under the collective heading of "hookworm infection". They differ most obviously in geographical distribution, structure of mouthparts, and relative size.

<span class="mw-page-title-main">Cutaneous larva migrans</span> Medical condition

Cutaneous larva migrans is a skin disease in humans, caused by the larvae of various nematode parasites of the hookworm family (Ancylostomatidae). The parasites live in the intestines of dogs, cats, and wild animals; they should not be confused with other members of the hookworm family for which humans are definitive hosts, namely Ancylostoma duodenale and Necator americanus.

<span class="mw-page-title-main">Parasitic worm</span> Large type of parasitic organism

Parasitic worms, also known as helminths, are large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schistosomes reside in blood vessels.

<i>Ancylostoma duodenale</i> Species of the roundworm genus Ancylostoma

Ancylostoma duodenale is a species of the roundworm genus Ancylostoma. It is a parasitic nematode worm and commonly known as the Old World hookworm. It lives in the small intestine of hosts such as humans, cats and dogs, where it is able to mate and mature. Ancylostoma duodenale and Necator americanus are the two human hookworm species that are normally discussed together as the cause of hookworm infection. They are dioecious. Ancylostoma duodenale is abundant throughout the world, including Southern Europe, North Africa, India, China, southeast Asia, some areas in the United States, the Caribbean, and South America.

Uncinaria stenocephala is a nematode that parasitizes dogs, cats, and foxes as well as humans. It is rare to find in cats in the United States. Uncinaria stenocephala is the most common canine hookworm in cooler regions, such as Canada and the northern regions of the US, where it can be found primarily in foxes (40%). U. stenocephala is also one of the most common hookworms in the UK, called the northern hookworm, however it has a rather low prevalence. U. stenocephala is also considered to be zoonotic hookworms because they live in animals but can be transmitted to humans.

The soil-transmitted helminths are a group of intestinal parasites belonging to the phylum Nematoda that are transmitted primarily through contaminated soil. They are so called because they have a direct life cycle which requires no intermediate hosts or vectors, and the parasitic infection occurs through faecal contamination of soil, foodstuffs and water supplies. The adult forms are essentially parasites of humans, causing soil-transmitted helminthiasis (STH), but also infect domesticated mammals. The juveniles are the infective forms and they undergo tissue-migratory stages during which they invade vital organs such as lungs and liver. Thus the disease manifestations can be both local and systemic. The geohelminths together present an enormous infection burden on humanity, amounting to 135,000 deaths every year, and persistent infection of more than two billion people.

<span class="mw-page-title-main">Strongylida</span> Suborder of roundworms

The Strongylida suborder includes many of the important nematodes found in the gastrointestinal tracts of ruminants, horses, and swine, as well as the lungworms of ruminants and the hookworms of dogs and cats.

<span class="mw-page-title-main">Ancylostomiasis</span> Medical condition

Ancylostomiasis is a hookworm disease caused by infection with Ancylostoma hookworms. The name is derived from Greek ancylos αγκύλος "crooked, bent" and stoma στόμα "mouth".

Necatoriasis is the condition of infection by Necator hookworms, such as Necator americanus. This hookworm infection is a type of helminthiasis (infection) which is a type of neglected tropical disease.

<i>Oesophagostomum</i> Genus of roundworms

Oesophagostomum is a genus of parasitic nematodes (roundworms) of the family Strongylidae. These worms occur in Africa, Brazil, China, Indonesia and the Philippines. The majority of human infection with Oesophagostomum is localized to northern Togo and Ghana. Because the eggs may be indistinguishable from those of the hookworms, the species causing human helminthomas are rarely identified with accuracy. Oesophagostomum, especially O. bifurcum, are common parasites of livestock and animals like goats, pigs and non-human primates, although it seems that humans are increasingly becoming favorable hosts as well. The disease they cause, oesophagostomiasis, is known for the nodule formation it causes in the intestines of its infected hosts, which can lead to more serious problems such as dysentery. Although the routes of human infection have yet to be elucidated sufficiently, it is believed that transmission occurs through oral-fecal means, with infected humans unknowingly ingesting soil containing the infectious filariform larvae.

<span class="mw-page-title-main">Hookworm vaccine</span>

Hookworm vaccine is a vaccine against hookworm. No effective vaccine for the disease in humans has yet been developed. Hookworms, parasitic nematodes transmitted in soil, infect approximately 700 million humans, particularly in tropical regions of the world where endemic hookworms include Ancylostoma duodenale and Necator americanus. Hookworms feed on blood and those infected with hookworms may develop chronic anaemia and malnutrition. Helminth infection can be effectively treated with benzimidazole drugs, and efforts led by the World Health Organization have focused on one to three yearly de-worming doses in schools because hookworm infections with the heaviest intensities are most common in school-age children. However, these drugs only eliminate existing adult parasites and re-infection can occur soon after treatment. School-based de-worming efforts do not treat adults or pre-school children and concerns exist about drug resistance developing in hookworms against the commonly used treatments, thus a vaccine against hookworm disease is sought to provide more permanent resistance to infection.

<i>Ancylostoma braziliense</i> Species of worm

Ancylostoma braziliense is a species of hookworm belonging to the genus Ancylostoma. It is an intestinal parasite of domestic cats and dogs. Severe infection is often fatal to these pets, especially in puppies and kittens. The infection is particularly endemic in the southern United States. It is most often confused with the zoonotic hookworm species Ancylostoma ceylanicum because of their uncanny resemblance.

<i>Ancylostoma caninum</i> Species of roundworm

Ancylostoma caninum is a species of nematode known as a hookworm, which principally infects the small intestine of dogs. The result of A. caninum infection ranges from asymptomatic cases to death of the dog; better nourishment, increasing age, prior A. caninum exposure, or vaccination are all linked to improved survival. Other hosts include carnivores such as wolves, foxes, and cats, with a small number of cases having been reported in humans.

<span class="mw-page-title-main">Ancylostomatidae</span> Family of roundworms

The Ancylostomatidae are a family of worms that includes the hookworms.

<i>Nippostrongylus brasiliensis</i> Species of roundworm

Nippostrongylus brasiliensis is a gastrointestinal roundworm that infects rodents, primarily rats. This worm is a widely studied parasite due to its simple lifecycle and its ability to be used in animal models. Its lifecycle similar to the human hookworms Necator americanus and Ancylostoma duodenale which includes five molting stages to become sexually mature.

<span class="mw-page-title-main">Soil-transmitted helminthiasis</span> Roundworm infection contracted from contaminated soil

Soil-transmitted helminthiasis is a type of worm infection (helminthiasis) caused by different species of roundworms. It is caused specifically by those worms which are transmitted through soil contaminated with faecal matter and are therefore called soil-transmitted helminths. Three types of soil-transmitted helminthiasis can be distinguished: ascariasis, hookworm infection and whipworm infection. These three types of infection are therefore caused by the large roundworm A. lumbricoides, the hookworms Necator americanus or Ancylostoma duodenale and by the whipworm Trichuris trichiura.

Ancylostoma ceylanicum is a parasitic roundworm belonging to the genus Ancylostoma. It is a hookworm both of humans and of other mammals such as dogs, cats, and golden hamsters. It is the only zoonotic hookworm species that is able to produce symptomatic infections in humans, with the majority of cases being in Southeast Asia.

References

  1. 1 2 3 4 5 6 7 8 "Zoonotic Hookworms" (PDF). cfsph.iastate.edu. Iowa State University. November 2013. Archived (PDF) from the original on February 29, 2020. Retrieved January 23, 2021.
  2. Hotez, Peter. "Hookworm and Poverty".
  3. Timmins, Lawrence (May 28, 2023). "Hookworm In Domestic Cats". Pet Ploy.
  4. Traub, Rebecca J. (2013). "Ancylostoma ceylanicum, a re-emerging but neglected parasitic zoonosis". Int J Parasitol. 43 (12–13): 1009–1015. doi:10.1016/j.ijpara.2013.07.006. PMID   23968813.
  5. Seguel, M.; Gottdenker, N. (2017). "The diversity and impact of hookworm infections in wildlife". Int J Parasitol Parasites Wildl. 6 (3): 177–194. doi:10.1016/j.ijppaw.2017.03.007. PMC   5526439 . PMID   28765810.
  6. 1 2 Markell, Edward K.; John, David C.; Petri, William H. (2006). Markell and Voge's medical parasitology (9th ed.). St. Louis, MO: Elsevier Saunders. ISBN   978-0-7216-4793-7.
  7. "Ancylostoma duodenale". Animal Diversity Web.
  8. Hotez, PJ; Bethony, J; Bottazzi, ME; Brooker, S; Buss, P (March 2005). "Hookworm: "the great infection of mankind"". PLOS Medicine. 2 (3): e67. doi: 10.1371/journal.pmed.0020067 . PMC   1069663 . PMID   15783256.
  9. "CDC Factsheet: Hookworm" Archived September 4, 2010, at the Wayback Machine
  10. 1 2 3 "CDC - Hookworm - Frequently Asked Questions (FAQs)". cdc.gov. Centers for Disease Control and Prevention. 17 September 2020. Archived from the original on December 21, 2020. Retrieved January 23, 2021.
  11. 1 2 Bleakley, Hoyt (2007). "Disease and Development: Evidence from Hookworm Eradication in the American South". The Quarterly Journal of Economics. 122 (1): 73–117. doi:10.1162/qjec.121.1.73. ISSN   0033-5533. PMC   3800113 . PMID   24146438.
  12. Dickson, Rumona; Awasthi, Shally; Williamson, Paula; Demellweek, Colin; Garner, Paul (June 24, 2000). "Effects of treatment for intestinal helminth infection on growth and cognitive performance in children: systematic review of randomised trials". BMJ: British Medical Journal. 320 (7251): 1697–1701. doi:10.1136/bmj.320.7251.1697. ISSN   0959-8138. PMC   27412 . PMID   10864543.
  13. "CDC - Hookworm - Treatment". cdc.gov. Centers for Disease Control and Prevention. 17 April 2019. Archived from the original on November 26, 2020. Retrieved January 23, 2021.
  14. 1 2 Mckenna, Megan L.; McAtee, Shannon; Bryan, Patricia E.; Jeun, Rebecca; Ward, Tabitha; Kraus, Jacob; Bottazzi, Maria E.; Hotez, Peter J.; Flowers, Catherine C.; Mejia, Rojelio. "Human Intestinal Parasite Burden and Poor Sanitation in Rural Alabama".
  15. Whitehead, Nadia. "The U.S. Thought It Was Rid Of Hookworm. Wrong".
  16. Sanders, John W.; Goraleski, Karen A. "The Hookworm Blues: We Still Got 'em".

Further reading