Control programs for strongyloidiasis in areas of high endemicity: an economic analysis of different approaches

Progress towards the implementation of control programmes for strongyloidiasis in endemic areas: estimation of number of adults in need of ivermectin for strongyloidiasis

The World Health Organization has started a process to issue guidelines for the control of strongyloidiasis. The guidelines might recommend to implement preventive chemotherapy (PC) at community level (i.e. to all individuals above 5 years of age), over a defined prevalence threshold. We previously estimated the number of school-age children (SAC) who would need PC. Here we estimate the number of people above 15 years of age who might be included in PC for strongyloidiasis. Based on previous Strongyloides prevalence estimates and on countries' age distribution, we retrieved the number of adults in need of PC. We then subtracted the number of people already involved in ivermectin mass distribution for the elimination of onchocerciasis and lymphatic filariasis and people living in countries where Loa loa is endemic. The number of adults to be involved in PC was estimated at 905.4 (95% confidence interval (CI): 520.6-1177.2), 660.2 (95% CI: 512.7-1214.9), and 512.1 (95% CI: 276-719.4) million people, when the strongyloidiasis prevalence threshold for implementing PC was set to 10%, 15% and 20%, respectively. Estimates at country level are also provided.These estimates might help endemic countries wishing to implement PC for strongyloidiasis to allocate resources to include adults in addition to SAC in control programmes. This article is part of the Theo Murphy meeting issue 'Strongyloides: omics to worm-free populations'.

Ivermectin and albendazole coadministration: opportunities for strongyloidiasis control

In 2020, WHO recognised the importance of strongyloidiasis alongside soil-transmitted helminths (STH) in their 2021-30 roadmap, which aspires to target Strongyloides stercoralis with preventive chemotherapy by use of ivermectin. Combination treatment with both albendazole, the primary drug used to treat STH, and ivermectin, would improve the efficiency of mass drug administration targeting both STH and S stercoralis. In this Personal View, we discuss the challenges and opportunities towards the development of an efficient control programme for strongyloidiasis, particularly if it is to run concurrently with STH control. We argue the need to define the prevalence threshold to implement preventive chemotherapy for S stercoralis, the target populations and optimal dosing schedules, and discuss the added benefits of a fixed-dose coformulation of ivermectin and albendazole. Implementation of an efficient control programme will require improvements to current diagnostics, and validation of new diagnostics, to target and monitor S stercoralis infections, and consideration of the challenges of multispecies diagnostics for S stercoralis and STH control. Finally, the evolution of ivermectin resistance represents a credible risk to control S stercoralis; we argue that genome-wide approaches, together with improved genome resources, are needed to characterise and prevent the emergence of resistance. Overcoming these challenges will help to reduce strongyloidiasis burden and enhance the feasibility of controlling it worldwide.

The diagnosis of human and companion animal Strongyloides stercoralis infection: Challenges and solutions. A scoping review

Strongyloidiasis is the infection caused by soil-transmitted nematodes of Strongyloides species, infecting humans and some animals. Strongyloides stercoralis is the species with most clinical and epidemiological relevance in humans and dogs, due to its high prevalence and its capacity of inducing a life-threatening hyperinfection. Diagnosis of strongyloidiasis is challenging, due to the absence of a single reference standard test with high sensitivity and specificity, which also hampers the estimation of the accuracy of other diagnostic tests. In this chapter, we review the deployment and performance of the parasitological, immunological, molecular tests for the diagnosis of strongyloidiasis in humans and in dogs. Further, we comment the available evidence from genotyping studies that have addressed the zoonotic potential of S. stercoralis. Finally, we discuss the use of different diagnostic methods in relation to the purpose (i.e., screening, individual diagnosis, inclusion in a clinical trial) and the setting (endemic/non-endemic areas) and report the accuracy figures reported by systematic reviews on either parasitological, serological or molecular techniques published in literature.

Soil-Transmitted Helminths and Anaemia: A Neglected Association Outside the Tropics

Anaemia is an important cause of morbidity and mortality globally. Among infectious agents responsible for anaemia, helminthic infections are often neglected, particularly in non-endemic countries. However, they should not be neglected in this setting, as international travel and migration are on the rise. In this narrative review, we aimed to describe soil-transmitted helminths as a cause of or contributing factor to anaemia, focusing on hookworms (Necator americanus and Ancylostoma duodenale), the whipworm (Trichuris trichiura), the roundworm (Ascaris lumbricoides), and the threadworm (Strongyloides stercoralis). A general review on the epidemiology, lifecycle, and clinical spectrum of anaemia is proposed, with a special focus on helminthic infections’ association with anaemia as well as the diagnostic approach, which are both particularly important in non-endemic settings.