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Strongyloides

Unlike other parasites that require a constant host for their lifecycle, Strongyloides has the capacity to transform and alternate between living as a parasite inside of a host, and existing as a free-living organism in soil. It can also complete its entire lifecycle and reproduce inside of the host's body. Once the infective larva comes into contact with the host’s skin and burrows into the body, it reproduces in the hosts bowels, where the eggs hatch and begin the life cycle again. Some of the larvae come out through the feces, while others “autoinfect” the host, by burrowing into the tissues of the anus and continuously begin their life cycle anew. Because of their capacity for host autoinfection,…

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 Strongyloides stercoralis: A Neglected but Fatal Parasite

Strongyloidiasis, a disease caused by Strongyloides stercoralis, continues to persist as a worldwide public health issue. However, the real burden of this disease is unknown, and studies have been performed in limited geographical areas and populations.

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Chronic strongyloidiasis – Don’t look and you won’t find

The presence of live larvae, rather than eggs, in fresh faecal specimens is a feature of S. stercoralis. Ivermectin is currently the most effective therapy for the eradication of 
S. stercoralis. Albendazole can be used when ivermectin is not suitable. Think of strongyloidiasis before starting a patient on immunosuppressant therapy, including corticosteroids, especially those from endemic areas or with unexplained eosinophilia.

Strongyloides

Strongyloides stercoralis is a small nematode with free-living forms found in soil, while parasitic forms (i.e., the adult female measuring 2.2mm in length) live within intestinal crypts in the duodenum, the jejunal mucosal villi, or in the submucosa; the male does not enter the intestinal mucosa but is passed in the stool.

Strongyloides stercoralis (Parasitic Roundworm)- A Threadworm

Strongyloides stercoralis is a parasitic roundworm that causes strongyloidiasis. It is commonly called a threadworm in the US. It is the smallest nematode known to cause infection in humans. They are unique among nematode because it has both parasitic and free-living form.

The biology of Strongyloides spp.

The life-cycle of Strongyloides is both complicated and somewhat tricky to understand, but also one part of the fascination of the genus. This description is primarily based on the life-cycle of S. ratti (a parasite of the rat), which has been extensively studied; some of these details are likely to vary in other species.

What are Strongyloides?

The current methods for diagnosing strongyloidiasis include duodenal drainage, immunological tests (IFA, IHA, EIA, ELISA) and stool examination. The key to diagnosis is to find the pathogen, so repeat stool testing is the best method.

Resources

WormBase ParaSite

The nematode Strongyloides stercoralis, or human threadworm, is a wide-spread, minute gastro-intestinal parasite of humans, occurring principally in the tropics and sub-tropics. Infection of immunosuppressed individuals can result in disseminated strongyloidiasis, in which worms occur throughout the body and can be fatal.

CDC

The rhabditid nematode (roundworm) Strongyloides stercoralis is the major causative agent of strongyloidiasis in humans. Rarer human-infecting species of Strongyloides are the zoonotic S. fuelleborni (fülleborni) subsp. fuelleborni and S. fuelleborni subsp. kellyi, for which the only currently known host is humans. Strongyloides spp. are sometimes called “threadworms” (although in some countries this common name refers to Enterobius vermicularis).

Fun With Microbiology

Autoinfection can occur with Strongyloides. Rhabditiform larvae within the intestine can develop into the infective filariform larvae as they pass through the bowel. These larvae can then reinfect the host by once again penetrating the bowel, traveling through the circulatory system to the lungs where they once again cycle through to reach the intestine or be finally passed out of the body in faeces.

StatPearls

Despite its ability to cause life-threatening diseases, strongyloidiasis is one of the most neglected tropical diseases. Moreover, Strongyloides infection can last the host's lifetime due to its ability to cause autoinfection of the host. The helminth S. stercoralis mainly infects humans but also occurs naturally in domestic dogs, cats, and primates.

WHO

Diagnosis of strongyloidiasis is not standardized. The most frequent procedure entails direct examination of stool specimens with enrichment and/or stool culture, but this often does not yield positive results even when the disease is present. Alternative tests (serology and polymerase chain reaction) are more efficient. Ivermectin, thiabendazole and albendazole are the most effective medicines for treating the infection. Albendazole is considered the least effective. Ivermectin, the drug of choice, is not available in all endemic countries. Moreover, the optimal schedule has yet to be defined.