Strongyloides stercoralis

Epidemiology

• free-living cycle of development in soil
• rhabditiform larvae passed in feces may transform into infectious filariform larvae either directly or after a free living phase in the soil
• distributed in tropical, humid regions, especially south- east Asia, sub-Saharan Africa, Carribean & Brazil
• in the USA, it is endemic in parts of the south
• humans & dogs may serve as definitive hosts

Pathology

• humans acquire infection through contact with fecally-contaminated soil containing infectious filariform larvae
• filariform larvae penetrate the skin or mucous membranes 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
• larvae mature into adult worms that penetrate the mucosa of the proximal small bowel
• adult females (2 mm in length) reproduce by parthenogenesis; males do not exist
• eggs hatch locally within the intestinal mucosa releasing rhabditiform larvae that migrate to the lumen to pass inthe feces or develop directly into filariform larvae that penetrate the colonic wall or perianal skin
• after gaining access to the bloodstream, the cycle of migration & internal reinfection permits infection for decades without further exposure to infectious larvae
• in immnocompetent hosts the immune system prevents the number of worms from increasing but cannot clear the infection completely, with the host chronically releasing infectious larvae into the feces
• in immunocompromised host
  • large numbers of larvae can disseminate widely invading the peritoneum, lungs, liver, kidney & central nervous system
  • the mucosal barrier may be disrupted giving access of intestinal flora to the bloodstream & peritoneum
  • mortality is high
• histology image; life cycle illustration

Clinical manifestations

• patients may be asymptomatic for decades
• recurrent urticaria often involving the buttocks & wrists
• migrating larvae can elicit a pathognomonic serpinginous eruption (larva currens "running larva")
  • pruritic, raised, erythematous lesion
  • advances as much as 10 cm/hr along the course of larval migration
• midepigastric pain aggravated by food ingestion
• nausea, diarrhea, GI bleeding, mild chronic colitis & weight loss may occur
• pulmonary symptoms are rare
• abdominal rash (case report with image)

Laboratory

• complete blood count
  • anemia
  • eosinophilia is common
• Strongyloides stercoralis serology 1st line test NEJM
  • Strongyloides stercoralis IgG in serum
  • Strongyloides stercoralis IgM in serum
• diagnosis is made by finding of rhabditiform larvae in feces
  • 200-250 um long
  • short buccal cavity indistinguishable from hookworm larvae
  • serial examinations may be required (only 33% are positive on 1st stool specimen)
• eggs are seldom seen in feces because they hatch in the intestine
• duodenojejunal samplings by aspiration, biopsy or the Enterotest string method
• Strongyloides stercoralis DNA
• disseminated Strongyloidiasis (immunosuppressed patients)
  • filariform larve (550 um long) may be seen in feces
  • sputum, bronchoalveolar lavage or surgical drainage fluid should be examined
  • blood cultures may show polymicrobial gram-negative bacteremia

Diagnostic procedures

• upper GI endoscopy
  • moderate to severe duodenitis
  • small bowel biopsy: chronic inflammation in the lamina propria

Radiology

• CT of abdomen may show enteritis with active infection

Complications

• strongyloides hyperinfection syndrome, including disseminated strongyloidiasis can occur in patients with chronic strongyloidiasis & immunodeficiency or immunosuppression
  • bacterial meningitis
  • bacterial endocarditis
  • case report (images)

Management

• even asymptomatic patients should be treated because of potential for fatal hyperinfection
• testing for Strongyloides prior to immunsuppression in patients at risk
• thiabendazole 25 mg/kg BID for 2 days
• disseminated Strongyloidiasis
  • only thiabendazole has been shown to be effective
  • 25 mg/kg BID for 5-7 days or until organism is erradicated
• therapy should be monitored with repeated feces examination
• ivermectin 200 ug/kg/day for 1-2 days
• albendazole 400 mg QD for 3 days may be superior

More general terms

• Strongyloides

Additional terms

• albendazole (Albenza)
• ivermectin (Stromectol, Sklice)
• mebendazole (Vermox, Emverm)
• thiabendazole (Mintezol)