A new study by the STOP consortium validates a simple, sensitive and low-cost diagnostic method that will help better estimate the burden of this neglected tropical disease
Infection by the intestinal parasite Strongyloides stercoralis may be severe and even life-threatening in people who are immunocompromised. It affects an estimated 386 million people worldwide, but the real prevalence of this neglected tropical disease is unknown due to a lack of sensitive diagnostic tools.
“In fact, among the different soil-transmitted helminths (STH), Strongyloides stercoralis is the most neglected of all, both in diagnostics and control strategies,” says Wendemagegn Enbiale, researcher at the Bahir Dar University in Ethiopia and senior author of the study. Different diagnostic approaches are used in different parts of the world and there is no standard diagnostic approach which can be used for routine diagnostic services and field studies.
The aim of this study was to improve the standard microscopy-based technique for the diagnosis of S. stercoralis, particularly when performing large-scale studies. To do so, researchers of the STOP consortium compared different protocols of the commonly used Baermann methods which allow larvae to separate from the stool sample before detecting them under the microscope. The team analysed 437 stool samples collected in the community of Zenzelima, in Northwest Ethiopia using three different techniques in parallel: the conventional Baermann technique (CB), the modified Baermann (MB), and the modified technique with charcoal pre-incubation (MBCI).
The results show there is a high prevalence of S. stercoralis infection in the region: larvae were detected in almost 35% of stool samples. The results also show that the modified Baermann with charcoal pre-incubation technique works significantly better than the others in recovering S. stercoralis larvae. It detected larvae in 31.3% of the samples, while the conventional Baermann only detected them in 9.6% of the samples. “Conventional Baermann is by far the commonly used method in routine diagnostic but our results show that it significantly underestimates the true burden of the disease,” says Woyneshet Gelaye, first author of the study. “This can lead to the exclusion of S. stercoralis from deworming programs,” she adds. The sensitivity of the MBCI (i.e. its capacity to detect positive samples) was almost 4-times higher (87%) than that of the conventional or modified Baermann (26.7% and 22.1%, respectively). Furthermore, the technique is relatively easy to implement, simple to perform, and comparatively cheaper. “It also uses less quantity of stool, which is important when conducting large-scale screenings for clinical trials, which is exactly what we want to do in our STOP project” explains Nana Aba Williams, researcher at ISGlobal and scientific coordinator of the project.
For Enbiale, this study is important because “it provides a simple, sensitive and low-cost diagnostic method which is sorely needed for case detection, mapping of the disease and proper evaluation of treatment outcomes, especially in large-scale studies.”
Woyneshet Gelaye, Nana Aba Williams, Stella Kepha et al. Performance evaluation of Baermann techniques: the quest for developing a microscopy reference standard for the diagnosis of Strongyloides stercoralis. Plos Negl Trop Dis.