Necator americanus

Source: Wikipedia, the free encyclopedia.

Necator americanus
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Nematoda
Class: Chromadorea
Order: Rhabditida
Family: Ancylostomatidae
Genus: Necator
Species:
N. americanus
Binomial name
Necator americanus
(Stiles, 1902)
Synonyms

Uncinaria americanus Stiles, 1902

Necator americanus is a species of

helminth) 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.[1] 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 (also known as Old World hookworm) 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.[2]

Necator americanus has been proposed as an alternative to Trichuris suis in helminthic therapy.[3]

Morphology

This

parasite has two dorsal and two ventral cutting plates around the anterior margin of the buccal capsule. It also has a pair of subdorsal and a pair of subventral teeth located close to the rear. Males are usually 7–9 mm long, whereas females are about 9–11 mm long. The typical lifespan of these parasites is 3–5 years. They can produce between 5,000 and 10,000 eggs per day.[4]

Habitat

N. americanus is primarily found in tropical and temperate areas. This parasite thrives in warmer climates because to hatch, the eggs require a moist, warm, and shaded environment. The thin, smooth shells of this species cause the eggs and juveniles to die in freezing temperatures or with soil desiccation. Therefore, the type of soil where the parasite resides is also very important for their ideal living conditions. Ideal soil conditions tend to be in areas where water is able to drain at a standard pace, and the size of the soil particles is neither too large nor too small. That way, the degree of dampness, as well as the openings in the soil, allow the parasites to burrow to the surface and attach to the skin of their next host. High transmission rates seem to be congruent with the heavy rains and warm temperatures that are characteristic of tropical climates. One anomaly of this species is that it appears to prefer male hosts to female hosts, likely because of the division of labor in regions of its prevalence.[5]

Lifecycle

Life cycle of N. americanus inside and outside of the human body

This worm starts out as an

trachea, where it is swallowed and carried to the small intestine. There, it attaches to the intestinal wall, and matures into an adult and begins reproduction. Adults live in the lumen of the intestinal wall, where they cause blood loss to the host. The eggs produced by the adults end up on the soil after leaving the body through the feces; female hookworms produce up to 30,000 eggs per day.[7][8]
On average, most adult worms are eliminated in 1–2 years. The N. americanus lifecycle only differs slightly from that of A. duodenale. N. americanus has no development arrest in immune hosts and it must migrate through the lungs.

Pathogenesis and symptoms

The pathology of N. americanus is divided into two stages – larvae and adults. The larvae penetrate the uninfected skin and travel through various organs, including the

dyspnea (short of breath) during larval migration. Once attached to the intestinal wall, N. americanus resides and matures into adults, penetrates blood vessels, and sucks blood. The incubation process of the larvae begins once entered into the small intestine; therefore, symptoms may not arise for up to 40 days, but this is variable from person to person.[9] Blood loss from sites of intestinal attachment may cause iron-deficiency anemia and protein loss.[8] One individual N. americanus can cause 30 μl of blood loss per day.[10] Iron-deficiency anemia can cause intellectual disability and growth insufficiency in children. Further, infected patients experience abdominal pain (exacerbated by meals) with diarrhea, bloating, and nausea.[11]

Epidemiology

In the United States, 95% of human hookworm cases are caused by N. americanus, primarily in young school children in economically deprived rural areas. Historically, there have been high rates of infection among children in the American South.[12] Juveniles cannot survive freezing temperatures, so the highest prevalence occurs in areas with warmer temperatures and greater rainfall. The greatest incidence of infections occurs in Asia and sub-Saharan Africa, especially in poverty-stricken areas with poor sanitation.[8] A. duodenale infections occur at a lesser rate and are seen primarily in Europe and the Mediterranean.[13]

Genome

A draft assembly of the genome of Necator americanus has been sequenced and analyzed.

immunomodulator proteins, whose products may be beneficial in treating inflammatory diseases and asthma.[15]

Diagnostics

The most common method for diagnosing N. americanus is through identification of eggs in a fecal sample using a microscope. N. americanus eggs have a thin shell and are oval shaped, measuring roughly 56–74 by 36–40 μm.[16]

Treatments

The most common

microtubule polymerization within the parasite.[17] The efficacy of single-dose treatments for hookworm infections were: 72% for albendazole, 15% for mebendazole, and 31% for pyrantel pamoate.[18] A current concern with this parasite is the increase in drug resistance, such as benzimidazoles and mebendazoles.[19]

Pregnant women should not be treated within their first trimester.[9]

During the 1940s, the treatment of choice was tetrachloroethylene,[20] given as 3 to 4 cc in the fasting state, followed by 30 to 45 g of sodium sulfate. Tetrachloroethylene was reported to have a cure rate of 80 percent for Necator infections, but 25 percent in Ancylostoma infections, and often produced mild intoxication in the patient.

Prevention and control

Infection and

transmission of others can be prevented by not defecating outdoors or using human feces as fertilizer.[21] This parasite is not transmittable directly from person to person.[9] Pigs may be an intermediate host for N. americanus.[1]

Economic burden

N. americanus causes hookworm diseases, which are associated with

fatigue, iron deficiency, and abdominal pain. The symptoms worsen and result in possible death when the infestation reaches over 500 hookworms. Children and pregnant women affected by N. americanus are at greater risk due to anemia and the greater need for dietary iron and protein. The demand is high for an improvement of sanitation to reduce fecal contamination in regions with high prevalence of N. americanus infections. The current control strategies include a combination of mass drug administration for children at age 4–6 years to prevent or eliminate N. americanus infections.[22]

References

  1. ^ a b "Necator americanus". Animal Diversity Web. Archived from the original on 2018-04-18. Retrieved 2018-04-21.
  2. from the original on 2018-08-20. Retrieved 2018-08-20.
  3. .
  4. ^ Roberts, Janovy & Schmidt 2010
  5. ^ "Necator americanus". Animal Diversity Web. Archived from the original on 2018-04-18. Retrieved 2018-04-21.
  6. ^ "Hookworm (Intestinal) | CDC-DPDx". September 17, 2019. Archived from the original on 2009-12-15. Retrieved 2021-11-11..
  7. ^ "Hookworm disease". Encyclopædia Britannica. 2009. Archived from the original on 2021-11-11. Retrieved 2021-11-11.
  8. ^
    PMID 15783256
    .
  9. ^ a b c "Necator americanus". Archived from the original on 2018-04-19. Retrieved 2018-04-21.
  10. ISSN 1381-6128
    .
  11. .
  12. .
  13. . (N. americanus) is the native hookworm of Africa south of the Sahara and the only one found in parts of India. Ancylostoma and Necator occur together elsewhere in India, in much of China, in southeast Asia, in the islands of the South and Southwest Pacific, and in parts of Australia. ..., it is probable that the geographic boundaries between the two genera of human hookworms will disappear.
  14. .
  15. .
  16. .
  17. .
  18. .
  19. ^ "Drug resistance in hookworms". Archived from the original on 2018-04-21. Retrieved 2018-04-21.
  20. ^ "Clinical Aspects and Treatment of the More Common Intestinal Parasites of Man (TB-33)". Veterans Administration Technical Bulletin 1946 & 1947. 10: 1–14. 1948. Archived from the original on 2022-02-25. Retrieved 2021-07-14.
  21. ^ "Prevention & Control". Parasites: Hookworms. Centers for Disease Control and Prevention, U.S. Department of Health & Human Services. 2013. Archived from the original on 2017-05-24. Retrieved 2017-04-30.
  22. S2CID 4945916
    .

Further reading