Strongyloidiasis: Morphology And Life Cycle, Clinical Features, Diagnosis, Treatment And Prevention
How Can We Detect Strongyloidiasis
Strongyloidosis is infection of the small intestine by Strongyloides stercoralis. Adult females are small measuring 2 mm in length. They live in the mucosa of the duodenum and lay eggs.
Life Cycle: The eggs are laid inside the mucous membrane. Soon the eggs hatch and the rhabditiform larvae enter the intestinal lumen by breaking the mucosa. These larvae are seen in fresh stools and their spring-like movement is diagnostic. Strongyloides stercoralis is known to take one of three life cycles.
- In the soil: They develop into infective filariform stage within three to four days. The larvae penetrate human skin to enter the blood vessels. An alternate mode of infection is accidental ingestion of infective larvae. They pass through the lungs and after a period of development, they are coughed up and swallowed. In the small intestine, they mature and copulate. Fertilized female burrows into the mucosa of the jejunum while the males are excreted in feces. Lifespan of the worm is not clearly known.
- Free-living cycle: Strongyloides stercoralis can develop as free living worms in the soil. The rhabditiform larvae in the soil may develop into free living adults, which reproduce in the soil independent of the human host. Under favourable conditions, the free-living larvae can change into filariform larvase which can enter the human skin and initiate a new cycle.
- Auto-infection: By this lifecycle, the worm perpetuates itself without leaving the host. The rhabditiform larvae change into filariform larvase in the large intestine or in the perianal skin. The latter penetrate the mucosa or skin to enter venules and reach the pulmonary circulation and develop further. In this way, the infection can persist in an individual for long periods even after leaving the endemic area.
How Strongyloidiasis Manifests On The Skin
Clinical Manifestations Of Strongyloidiasis
Clinical symptoms depend on the severity of infection and reactivity of the host. Mild infections may be asymptomatic.
Larval migration: Local allergy and infection may appear at the site of penetration by the larvae. The progress of the larvae through the skin and subcutaneous tissue may produce linear streaks of urticaria which progress at the rate of a few centimeters in an hour. Crops of these urticarial lesions recur for considerable periods. These are termed larva curens since they migrate fast. The pulmonary phase of the larvae may be associated with cough, fever, breathlessness and asthmatic symptoms. Hemoptysis may occur rarely.
Features attributed to the adult worm: Heavy infection may cause epigastric pain, nausea, vomiting and diarrhea. When the worm load is very heavy, symptoms of enterocolitis develop. Meningeal irritation is seen in a few cases.
How To Diagnose And Treat Strongyloidiasis
Diagnosis, Treatment And Prevention
Diagnosis: It is established by demonstrating the larvae or adult worms. Larvae can be demonstrated in fresh fecal samples. The larvae may be detected in the sputum during the pulmonary phase of migration. Accidentally, the duodenal aspirate may reveal the larvase and intestinal biopsy may bring out the adult worm. Transient mild eosinophilia is common.
Treatment: Once the infection is diagnosed, treatment must be given, irrespective of the symptoms. The drug of choice is thiabendazole which is available as tablets or syspension to be administered orally in a dose of 25 mg/Kg twice a day for 3 days. Thiabendazole is generally safe, but vomiting and vertigo may occur at times which are self-limiting. Clearance of the worms occurs in over 80% of cases. Repetition of the drug after 3 months may be necessary if the larvae are demonstrable in feces or allergic manifestations persist. Pruritus can be relieved by antihistamines.
Prevention: The general principles mentioned in the case of hookworms are applicable in the case of strongyloides, but treatment has to be repeated to eradicate the infection due to the phenomenon of auto-infection.
© 2014 Funom Theophilus Makama