Seroepidemiological trend of strongyloidiasis in the Bolivian Chaco (1987–2012) in the absence of disease-specific control measures

INTRODUCTION: The prevalence of s. stercoralis infection is grossly underestimated because infections go mostly undetected (due to a combination of the asymptomatic or paucisymptomatic nature of the infection and inaccurate diagnostics) though they can persist for a lifetime due to the worm autoinfective cycle. In the Bolivian Chaco, the prevalence of soil-transmitted nematodes dropped dramatically in the past 25 years, but mebendazole used for preventive chemotherapy has no effect on Strongyloides. Meanwhile, the prevalence of intestinal protozoan infections remains unchanged. AIM: To compare S. stercoralis seroprevalence in rural communities of the Bolivian Chaco from 1987 to 2012. METHODS: Sera collected during two previous sero-surveys, conducted in the Chaco region in 1987 and 2012, were tested for S. stercoralis using a commercial enzyme-linked immunosorbent assay (Bordier-ELISA, Bordier Affinity Products, Switzerland). RESULTS: 366 sera were analyzed, 122 from the 1987 survey and 244 from the 2012 survey. Seropositivity for S. stercoralis was significantly more prevalent in 1987 (19/122, 15.6% versus 18/244, 7.4% in 2012), accounted for the age classes 5–14 and 15–35 year-olds. Conversely, there was a non-statistically significant higher prevalence in the over 35 year-olds in 2012. Multivariate analysis showed a significant association between seropositivity for S. stercoralis and age in the 2012 population (OR 1.02 for each one-year increase, 95% CI 1.00–1.04), but none in 1987. CONCLUSIONS: There is a significant reduction in S. stercoralis seroprevalence in rural Bolivian Chaco, which cannot be explained by preventive chemotherapy or improved socialsanitary conditions. As the drop in seen in younger generations, it is consistent with little transmission occurring. The persistent higher prevalence in adults is a testimony of infections occurring in the past. However, the risk of transmission still exists, as these individuals represent a potential reservoir due to the lifelong nature of S. stercoralis infections.