When you hear the name strongyloidiasis, you likely think of an obscure disease in a far-off land. In fact, until recently, it was considered one of the most neglected of the neglected tropical diseases (NTDs), a set of debilitating parasitic and bacterial diseases that cause severe disability and affect more than one billion people around the world. What you might not have guessed, though, is that this treatable disease caused by an intestinal worm has also been found in parts of the southern United States, and that it is much more widespread than previously thought.
What is Strongyloidiasis?
Strongyloidiasis is an infection caused by the parasitic worm (also known as a soil-transmitted helminth) Strongyloides stercoralis. It is transmitted through contact with contaminated soil and thrives in areas with warm and moist climates with poor sanitation. Symptoms can include hives, abdominal pain, and diarrhea, and lead to a fatal syndrome in immunosuppressed individuals. It also can cause nutritional issues and stunting in children, which impacts their cognitive and physical development and can have lifelong effects on education and income.
If gone untreated, the parasite stays with you your whole life. Unlike other intestinal worms, however, there are currently no large-scale programs designed to distribute medicines and treat this disease, due in large part to a previous underestimation of the disease’s prevalence.
So, how widespread is strongyloidiasis globally? And what is needed to implement large-scale programming to control this disease?
We set out with a team of researchers from the World Health Organization (WHO) and the IRCCS Ospedale Sacro Cuore Don Calabria Hospital in Italy to fill this knowledge gap in two papers, “The Global Prevalence of Strongyloides stercoralis Infection,” and “Preventive chemotherapy for the control of strongyloidiasis in school-age children: Estimating the ivermectin need.”
In the first paper, our aim was to obtain a more accurate estimate of the global burden of this disease with data at the country level. Previous studies estimated that 30-100 million people were infected, but these estimates had been questioned due to an unclear source and methods as well as diagnostic performance issues. One key challenge in estimating the prevalence of this disease is that it is difficult to diagnose—none of the diagnostic tests that exist for other worm infections are considered a gold standard for strongyloidiasis.
We conducted a literature review and identified 146 articles with prevalence data from 1990 - 2016 from across 43 countries, then used a spatiotemporal statistical modeling approach to estimate the prevalence at the global and country level in 2017. Our analysis included high-, middle- and low-income countries.