Strongyloidiasis

Strongyloidiasis is primarily an infection of the small bowel by the filarial worm Strongyloides stercoralis
it is endemic in the tropics and subtropics but also seen in countries with temperate climates, people who have lived or travelled to these areas are also at risk
infection can be either acute or chronic in nature
Transmission of the infection may occur through:
- direct penetration of human skin by infective larvae when in contact with soil e.g. – walking barefoot
- oro-anal contact – seen in homosexual men
- solid organ transplants – there have been reports of transmission of the infection derived from the donor organ
- faecal-oral route – may be possible when larvae contaminated water is used to wash vegetables in endemic areas

Most infections are asymptomatic however immunosuppressed individuals may suffer gross infection.
Most infections are either mild or asymptomatic.
- In these patients an increase in peripheral blood eosinophil count is the only sign of infection

life-cycle
- Faecal soil contamination with S stercoralis larvae are most likely to be seen in rurual areas with poor sanitation.
- filariform larvae in the soil penetrate the skin when the host walks barefoot on contaminated soil
- parasitic cycle
  - larve enters venous circulation and migrate to the lungs.
  - They are coughed up and swallowed.
  - the larvae in the small intestine develops into adult female.
  - The reproduce asexually and release eggs into the digestive system
  - hatched eggs release non-infectious rhabditiform larvae which is excreted in stools and enter the soil
- free living cycle
  - these free-living rhabditiform larvae may mature into male and female adult worms, which reproduce sexually or transform directly into filariform larvae
  - S stercoralis parasite has the ability to reinfect the host through the wall of gastrointestinal system – known as autoinfection:
  - this is caused by rhabditiform larvae in the faeces which transforms into infectious filariform larvae inside the gastrointestinal system.
  - These filariform larvae penetrates the gut wall and enter the circulation and migrate to the lungs to begin the cycle again

characteristic cutaneous reaction following acute larvae invasion of the skin
most commonly affects the foot
may cause serpiginous or urticarial tracts with severe pruritus lasting for several days

intensely itchy red tracts seen in the perianal area and upper thighs due to rapid speed of intradermal migration (progressing at around 5-15 cm per hour) of the parasite in chronic infection
pathognomonic for strongyloidiasis

dry cough or wheeze
Loeffler’s-like syndrome
rare
characterised by fever, dyspnoea, wheeze, pulmonary infiltrates on chest radiographs, and accompanying blood eosinophilia

travelers or people who migrate from an endemic area and develop the following within 3-4 weeks of travel:
- persistent unexplained eosinophilia
- gastrointestinal symptoms: nausea, vomiting, abdominal pain, bloating
- pulmonary symptoms: fever, wheeze, persistent cough
- cutaneous symptoms: larva currens, hives, or pustules

three stool samples for microscopy – collected on separate days
- although the test has low sensitivity for detecting S stercoralis (around 50%) it is considered to be the gold standard for diagnosis
- larvae usually appear in stools 3-4 weeks after dermal penetration.
blood test for S stercoralis serology
- detects IgG to a filariform larval antigen

Repeat serological testing is used as an indicator of treatment efficacy
- a decrease in the antibody titre at 6-12 months after treatment is considered to be an indicator of eradication of the parasiTE
- a significant decrease in blood eosinophil count can also be used as an effective tool