Autoinfection and Hyperinfection With Strongyloides Stercoralis

Infection with Strongyloides stercoralis is frequently asymptomatic or may show few clinical signs. However on occasion it can persist for many years due to autoinfection and depending on the immune status of the individual, be life threatening with dissemination and hyperinfection.

Humans get infected with this nematode parasite by its ability to penetrate skin. They may be present in soil as free-living adults or as infective filariform larvae (this is the stage that can penetrate the skin). Hookworms are another parasite that can penetrate the skin to infect people.

The parasite then gets in the bloodstream and is carried to the lungs. They are carried up to the throat where they are swallowed and end up in the small intestine where they develop into adults.

If symptoms are present, you may see dermatitis of the skin at the point of entry, a cough and occasionally pneumonitis as the larvae pass through the lungs. Abdominal symptoms may occur after the parasite matures to adults resembling peptic ulcer, weight loss, vomiting and diarrhea.

Hives-like rashes may be seen in the area of the buttocks and around the trunk.

The female adult deposits eggs in the duodenum which later hatch as non-infective rhabditiform larvae which exit the body in the feces and later develop in the soil as either infective filariform larvae or free living adults. And the circle of life continues.

Autoinfection

This is a situation where the non-infective rhabditiform larvae become infective filariform larvae before leaving the body. The filariform larvae may penetrate the intestinal wall or the perianal skin to continue re-infecting the person. There are two roundworm infections that are capable of doing this; Strongyloides and Capillaria philippinensis. This can keep the individual infected for years (up to 35 years according to one text).

Hyperinfection

Rarely autoinfection with the increasing worm burden can lead to dissemination and hyperinfection of the individual. This typically occurs in the immunocompromised host, though not exclusively. People with HIV infection or those taking drugs that suppress the immune system are particularly vulnerable.

Disseminating strongyloidiasis can lead to pulmonary involvement, septicemia (secondary Gram-negative sepsis), shock, wasting and death.

Strongyloides are found worldwide, in tropical and temperate regions, however are more frequently seen in warm, wet areas.

Diagnosis of this infection is based on finding the larvae (primarily the rhabdtiform) in feces, using special techniques such as funnel techniques or by culture. It can also be by examining duodenal aspirates.

Treatment of strongyloides is with ivermectin. Those at risk of dissemination and hyperinfection definitely should be treated.

Good hygienic practices and especially the use of footwear can help prevent this parasitic infection.