Human strongyloidiasis is a parasitic disease caused by infection with the helminth Strongyloides stercoralis. It is included in WHO’s list of neglected tropical diseases within the group of soil-transmitted helminthiases. Widespread throughout the tropics, S. stercoralis infects an estimated 300–600 million people worldwide.
Strongyloidiasis has a wide range of clinical presentations, ranging from subclinical disease to diarrhoea, abdominal pain and urticaria, potentially leading to deadly complications due to hyperinfection and disseminated disease, especially in immunocompromised individuals.
Although the standard treatment for strongyloidiasis (oral medication with ivermectin) is easy to administer, no endemic country has a dedicated public health programme to address the disease. This is due to two main reasons: lack of technical directions on public health control of strongyloidiasis and limited access to ivermectin.
In some settings, preventive chemotherapy interventions based on mass drug administration of ivermectin to control lymphatic filariasis and onchocerciasis have indirectly benefited those affected by strongyloidiasis. The reduction in prevalence of S. stercoralis infection indicated that preventive chemotherapy with ivermectin may be a potential public health strategy in areas endemic for strongyloidiasis; however, no guidance existed on how this intervention should be implemented.
To fill this important normative gap, and at the request of health ministries of several countries in which strongyloidiasis is endemic, in 2023 WHO convened a guideline development group (GDG) of global experts, with the aim of formulating evidence-informed recommendations on whether preventive chemotherapy with ivermectin could reduce the burden of strongyloidiasis, and how this intervention should be implemented.
“This guideline is an important step towards addressing the burden of strongyloidiasis – we invite everyone to take note of its recommendations and operational modalities,” said Dr Jérôme Salomon, Assistant Director-General, Communicable and Noncommunicable diseases at WHO.
The GDG formulated a key recommendation supporting annual mass drug administration with single-dose ivermectin 200 µg/kg in all age groups from 5 years and above in endemic settings where prevalence of S. stercoralis infection among school-aged children equals or exceeds 5%.
The guideline also provides information on the guideline development process, shares details on evidence available in support of the recommendation made and highlights research needs to further WHO’s agenda on strongyloidiasis. It also discusses the rationale for the recommendation, considering benefits and harms, certainty of the evidence, values and preferences, resource use, equity, acceptability, feasibility and justification for the strength of the recommendation. Finally, it outlines details related to programmatic implementation of activities in the field, such as the recommended implementation unit (the district), the frequency of treatment (annual) and the minimum duration of the programme (5 years).
Challenges and next steps
The guideline acknowledges that implementation of mass drug administration of ivermectin in endemic settings may be made difficult by the scarcity of data on prevalence, burden and distribution of strongyloidiasis. However the magnitude of the population to be treated is expected to be significant in many parts of the world. Implementation might therefore depend on the donation of ivermectin to countries that cannot afford it. The elimination of onchocerciasis and lymphatic filariasis has been supported by the donation of ivermectin by a pharmaceutical company (MSD).
In line with its road map for neglected tropical diseases 2021–2030, WHO is encouraging countries, partners and the global community working on neglected tropical diseases to accelerate efforts to estimate the burden of strongyloidiasis, develop appropriate diagnostics, and support the scale-up of programmes on strongyloidiasis by facilitating their inclusion into national health policies and services and by mobilizing resources for their implementation. In addition, WHO is actively promoting the prequalification of generic ivermectin at affordable cost and/or the donation of this medicine, so as to strengthen access by all those in need. As of July 2024, two formulations of ivermectin tablets 3 mg have been successfully prequalified by WHO.
If the efforts of all partners are successful, WHO targets that by 2030 at least 96 countries globally will have included ivermectin in preventive chemotherapy interventions in all areas endemic for S. stercoralis.