This Review, written by the strongyloidiasis guidelines development group along with WHO and international experts, presents a summary of the recently published WHO guideline recommendation for strongyloidiasis.
Strongyloidiasis is a soil-transmitted helminthiasis that is estimated to affect 300–600 million people across Asia, Africa, South and central America, and the Pacific. This neglected parasitic disease is most known for its ability to persist as a lifelong infection due to autoinfection and its risk of hyperinfection and disseminated disease during immunosuppression, which has a more than 60% case fatality. Despite the large global burden of strongyloidiasis, there have been no large-scale public health programmes or WHO guidelines directed towards its control and elimination. However, over the past decade, key scientific and policy changes along with requests from endemic countries have led to WHO incorporating strongyloidiasis into its 2021–30 roadmap and public health targets for control and elimination of neglected tropical diseases. In 2024, WHO published its first guideline on public health control of strongyloidiasis with a single recommendation: in endemic settings with a Strongyloides stercoralis infection prevalence of 5% or higher (measured either with Baermann or agar plate culture from stool specimens), WHO conditionally recommends mass drug administration with single-dose ivermectin (200 μg/kg; oral therapy) in all age groups from 5 years and older to reduce strongyloidiasis. This Review, written by the 2023–24 strongyloidiasis guidelines development group along with WHO colleagues and international experts, presents a summary of the recently published WHO guideline recommendation for strongyloidiasis, and the supporting evidence, considerations for public health implementation, and future research needs.
Human strongyloidiasis is a soil-transmitted helminthiasis caused by infection with Strongyloides stercoralis, with an estimated 300–600 million people infected across Asia, Africa, South and central America, and the Pacific.1, 2 This neglected parasitic disease is most commonly found in regions with tropical or subtropical climates and poor sanitation and hygiene, in rural environments, and among socioeconomically disadvantaged groups. Chronic infection with S stercoralis causes a wide range of clinical presentations, often with minimal symptoms.3, 4 Two defining features of S stercoralis are its autoinfective lifecycle, leading to lifelong infection in the untreated host, and its capacity to cause hyperinfection and disseminated disease (often precipitated by an immunosuppressing event), which has a greater than 60% case fatality.
The lifecycle of S stercoralis is complex. Infection occurs when infective filariform larvae from contaminated soil directly penetrate the skin of the human definitive host. After infection, the larvae migrate via the heart and lungs, or directly, to the small intestine, where they reside and mature into adult female worms (the parasitic phase). These female worms produce eggs by parthenogenesis, which hatch into non-infectious rhabditiform larvae within the small intestine. The rhabditiform larvae have two potential pathways: they can be excreted in the stool and enter the environment; or they can directly develop into infective filariform larvae within the host's intestine and reinfect the individual via penetration of the intestine or perianal tissue (autoinfection). Autoinfection allows S stercoralis to complete its lifecycle entirely within the human host, leading to the potential for lifelong infection, Rhabditiform larvae, which are excreted into a suitable soil environment in stool, can develop via two pathways. They can directly moult into infective filariform larvae or they can develop into a free-living adult phase that mates via sexual reproduction. There is only one generation of this sexual free-living phase in the environment.9 The infective filariform larvae then seek a definitive host (humans, dogs, or other mammals) to complete the lifecycle; therefore, this parasite does have non-human definitive hosts.
Read the full article: "Review of the WHO guideline on preventive chemotherapy for public health control of strongyloidiasis"