Necator americanus (hookworm)

Epidemiology

• 25% of the world population is infected with hookworm, either Ancylostoma duodenale or Necator americanus
• eggs are deposited with feces in the soil where rhabditiform larvae hatch & develop in 1 week to infectious filariform larvae
• lifespan of Necator americanus is 3-10 years
• prevalent in the western hemisphere, & equatorial Africa
• distribution overlaps with Ancylostoma duodenale in southeast Asia
• older children & adults in rural areas using unsanitary farming methods are most commonly & heavily infested

Pathology

• infectious filariform larvae penetrate the skin of their host & reach the lungs via the bloodstream
• larvae invade the alveoli & are transported by host clearance mechanisms to the epiglottis where they are swallowed & gain access to the small intestine
• they use cutting plates to attach to the small bowel mucosa & suck blood
• adult females produce thousands of eggs daily which are passed into the feces
• penetration of the skin to the adult form takes 6-8 weeks
• larvae if swallowed may also develop into adults
• adult worms are about 1 cm long
• adults generally live 2-5 years

Clinical manifestations

• most infected individuals are asymptomatic
• iron deficiency anemia may result
• larvae may produce a pruritic maculopapular rash "ground itch" at the site of skin penetration
• larvae migrating through the lungs may produce a mild transient pneumonitis (less frequently than with Ascaris)
• epigastric pain & diarrhea may accompany early intestinal phase

Laboratory

• diagnosis is made by recovery of eggs in the feces
• eggs measure 40 by 60 um & are oval in shape
• rhabditiform larvae may be observed if eggs allowed to hatch after a delay in examination
• complete blood count (CBC)
  • microcytic, hypochromic anemia with chronic infection
  • eosinophilia with migratory phase
• serum albumin: hypoalbuminemia

Management

• the major consequence of chronic hookworm infection is iron deficiency anemia
• antihelmintic agents
  • mebendazole
  • pyrantel pamoate
  • albendazole
• ferrous gluconate 320 mg PO TID

More general terms

• Necator

Additional terms

• albendazole (Albenza)
• Loffler's syndrome (simple pulmonary eosinophilia)
• mebendazole (Vermox, Emverm)
• pyrantel (Antiminth)