Search
Necator americanus (hookworm)
Epidemiology:
1) 25% of the world population is infected with hookworm, either Ancylostoma duodenale or Necator americanus
2) eggs are deposited with feces in the soil where rhabditiform larvae hatch & develop in 1 week to infectious filariform larvae
3) lifespan of Necator americanus is 3-10 years [3]
4) prevalent in the western hemisphere, & equatorial Africa
5) distribution overlaps with Ancylostoma duodenale in southeast Asia
6) older children & adults in rural areas using unsanitary farming methods are most commonly & heavily infested
Pathology:
1) infectious filariform larvae penetrate the skin of their host & reach the lungs via the bloodstream
2) larvae invade the alveoli & are transported by host clearance mechanisms to the epiglottis where they are swallowed & gain access to the small intestine
3) they use cutting plates to attach to the small bowel mucosa & suck blood
4) adult females produce thousands of eggs daily which are passed into the feces
5) penetration of the skin to the adult form takes 6-8 weeks
6) larvae if swallowed may also develop into adults
7) adult worms are about 1 cm long
9) adults generally live 2-5 years
Clinical manifestations:
1) most infected individuals are asymptomatic
2) iron deficiency anemia may result
3) larvae may produce a pruritic maculopapular rash "ground itch" at the site of skin penetration
4) larvae migrating through the lungs may produce a mild transient pneumonitis (less frequently than with Ascaris)
5) epigastric pain & diarrhea may accompany early intestinal phase
Laboratory:
1) diagnosis is made by recovery of eggs in the feces
2) eggs measure 40 by 60 um & are oval in shape
3) rhabditiform larvae may be observed if eggs allowed to hatch after a delay in examination
4) complete blood count (CBC)
a) microcytic, hypochromic anemia with chronic infection
b) eosinophilia with migratory phase
5) serum albumin: hypoalbuminemia
Management:
1) the major consequence of chronic hookworm infection is iron deficiency anemia
2) antihelmintic agents
a) mebendazole
b) pyrantel pamoate
c) albendazole
3) ferrous gluconate 320 mg PO TID
Related
albendazole (Albenza)
Loffler's syndrome (simple pulmonary eosinophilia)
mebendazole (Vermox, Emverm)
pyrantel (Antiminth)
General
Necator
Properties
KINGDOM: animal
PHYLUM: helminth
References
- Clinical Diagnosis & Management by Laboratory Methods,
19th edition, J.B. Henry (ed), W.B. Saunders Co., Philadelphia,
PA. 1996, pg 1285-86
- Harrison's Principles of Internal Medicine, 13th ed.
Isselbacher et al (eds), McGraw-Hill Inc. NY,
1994, pg 917-18
- Grimm L
What's Eating You: 12 Common Intestinal Parasites.
Medscape. November 25, 2019
https://reference.medscape.com/slideshow/intestinal-parasites-6010996