Nematode Zoonoses - STRONGYLOIDIASIS

AGENT:

Strongyloidiasis is caused by infection with Strongyloides stercoralis.

RESERVOIR AND INCIDENCE:

The condition is an infection of humans, but dogs, cats, and primates have been found naturally infected. The disease is endemic in tropical and subtropical regions; although the prevalence is generally low, in some areas disease rates exceed 25%. In the USA, the disease is endemic in southern wet areas.

TRANSMISSION:

The parasite is uniquely capable of maintaining its life cycle both within the human host and in soil. Infection occurs when filariform larvae in soil penetrate the skin, enter the bloodstream, and are carried to the lungs, where they escape from capillaries into alveoli and ascend the bronchial tree to the glottis. The larvae are then swallowed and carried to the duodenum and upper jejunum, where maturation to the adult stage takes place. The parasitic female, generally held to be parthenogenetic, matures and lives embedded in the mucosa, where its eggs are laid and hatch. Rhabditiform larvae, which are noninfective, emerge, and most migrate into the intestinal lumen to leave the host via the feces. The life span of the adult worm may be as long as 5 years. In the soil, the rhabditiform larva metamorphose into the infective (filariform) larvae. However, the parasite also has a free-living cycle in soil, in which some rhabditiform larvae develop into adults that produce eggs from which rhabditiform larvae emerge to continue the life cycle. Internal autoinfection takes place in the lower bowel when some rhabditiform larvae, instead of passing with the feces, develop into filariform larvae that penetrate the intestinal mucosa, enter the intestinal lymphatic and portal circulation, are carried to the lungs, and return to the small bowel to complete the cycle.

DISEASE IN ANIMALS:

Young dogs and cats have thin skins which allow massive infection to penetrate, giving severe dermatitis, inappetence, coughing and even bronchopneumonia. Vomiting occurs, as does severe dermatitis during the period of larval penetration.

DISEASE IN MAN:

Pruritic dermatitis is seen at sites of larval penetration. Diarrhea, epigastric pain, nausea, malaise, weight loss, coughing, rales, transient pulmonary infiltrates are also seen. In the hyperinfection syndrome, autoinfection is greatly increased, resulting in a marked increase in the intestinal worm burden and in massive dissemination of filariform larvae to the lungs and most other tissues, where they can cause local inflammatory reactions and granuloma formation. Severe diarrhea, bronchopneumonia, and ileus can result.

DIAGNOSIS:

Diagnosis requires finding the larval stages in feces or duodenal fluid. ELISA and IFA serologic tests are being developed.

TREATMENT:

Thiabendazole, albendazole, mebendazole, cambendazole, ivermectin, or levamisole.

PREVENTION/CONTROL:

Rigid attention to hygienic habits, including use of footwear in endemic areas. Sanitary disposal of feces. Fecal exams of monkeys, dogs, and cats in quarantine.