Necator americanus

From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article is about the organism. For the infection, see Necatoriasis.
Necator americanus
Necator Americanus L3 x1000 12-2007.jpg
Scientific classification
Kingdom: Animalia
Phylum: Nematoda
Class: Secernentea
Order: Strongylida
Family: Ancylostomatidae
Genus: Necator
Species: N. americanus
Binomial name
Necator americanus

Necator americanus is a species of hookworm (a type of helminth) commonly known as the New World hookworm. Like other hookworms, it is a member of the phylum Nematoda. It is a parasitic nematode that lives in the small intestine of hosts such as humans, dogs, and cats. 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.[1]

Necator americanus has been proposed as an alternative to Trichuris suis in helminthic therapy.[2]

Morphology[edit]

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 three to five years. They can produce between 5000 and 10,000 eggs per day.[3]

Life cycle[edit]

Life cycle of Necator americanus inside and outside of the human body

This worm starts out as an unembryonated egg in the soil. After 24–48 hours under favorable conditions, the eggs become embryonated and hatch. This first juvenile stage 1 is known as 'rhabditiform'. The rhabditiform larvae grow and molt in the soil, transforming into a juvenile stage 2. The juvenile stage 2 molts once more until reaching the juvenile 3 stage, which is also called 'filariform'; this is also the infective form. The transformation from rhabditiform to the filariform usually takes five to 10 days.[4] This larval form is able to penetrate human skin, travel through the blood vessels and heart, and reach the lungs. Once there, they burrow through the pulmonary alveoli and travel up the trachea, where they are swallowed and are carried to the small intestine, where they mature into adults and reproduce by attaching themselves to the intestinal wall, causing an increase of blood loss by the host. The eggs end up on the soil after leaving the body through the feces.[5] On average, most adult worms are eliminated in one to two years. The N. americanus life cycle only differs slightly from that of A. duodenale. N. americanus has no development arrest in immune hosts and it must migrate through the lungs.

References[edit]

  1. ^ Georgiev VS (May 2000). "Necatoriasis: treatment and developmental therapeutics". Expert Opin Investig Drugs 9 (5): 1065–78. doi:10.1517/13543784.9.5.1065. PMID 11060728. 
  2. ^ Croese J, O'neil J, Masson J, et al. (January 2006). "A proof of concept study establishing Necator americanus in Crohn's patients and reservoir donors". Gut 55 (1): 136–7. doi:10.1136/gut.2005.079129. PMC 1856386. PMID 16344586. 
  3. ^ Roberts, Larry S., and John Janovy, Jr. Foundations of Parasitology. Seventh ed. Singapore: McGraw-Hill, 2006. Print.
  4. ^ "hookworm." CDC. 2009. CDC Online. 4 Dec. 2009. <http://www.dpd.cdc.gov/dpdx/HTML/Hookworm.htm>.
  5. ^ "hookworm disease." Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 15 May. 2009 <http://www.britannica.com/EBchecked/topic/271350/hookworm-disease>.

Further reading[edit]

  • Hotez,P.J.,and D.I.Pritchard.1995(June).Hookworm infection.Sci. Am. 272:68-74.
  • Murray,P.R.,K.S.Rosenthal,and M.A.Pfaller.2009.Medical Mirobiology,6th ed.Elsevier/Mosby Publishing Company,Philadelphia, U.S.A.,865 p.
  • Schmidt,G.D.,and L.S.Roberts.2009.Foundations of parasitology,8th ed.McGraw-Hill Companies,New York,p. 472-473.