Molecular Diagnostics for Soil-Transmitted Helminths

Abstract

Abstract. Historically, the diagnosis of soil-transmitted helminths (STHs) (e.g., Strongyloides stercoralis, Trichuris trichiura, Ancylostoma duodenale, Necator americanus, and Ascaris lumbricoides) has relied on often-insensitive microscopy techniques. Over the past several years, there has been an effort to use molecular diagnostics, particularly quantitative polymerase chain reaction (qPCR), to detect intestinal pathogens. While some platforms have been approved by regulatory bodies (e.g., Food and Drug Administration) to detect intestinal bacteria, viruses, and protozoa, there are no approved tests currently available for STH. Although studies comparing qPCR to microscopy methods for STH are imperfect, due in large part to a lack of a sufficient gold standard, they do show a significant increase in sensitivity and specificity of qPCR compared with microscopic techniques. These studies, as well as the advantages and disadvantages of using qPCR for STH diagnosis, are discussed. Guidelines for those designing future studies utilizing qPCR are proposed for optimizing results, as is the proposition for using standardized molecular diagnostics routinely for STH in clinical laboratories and for field-based studies when possible.

Comparison of multi-parallel qPCR and Kato-Katz for detection of soil-transmitted helminth infection among children in rural Bangladesh

“…Consistent with prior studies in low STH infection intensity settings, using qPCR led to substantial increases in hookworm detection and moderate increases in T. trichiura detection compared to 19,21,22,42). Poorer performance of Kato-Katz, particularly for hookworm, is likely due to rapid disintegration of hookworm ova following stool collection (42,52). However, we found that the detection rate for A. lumbricoides was 14% lower for qPCR than Kato-Katz.…”

“…A challenge in studies assessing accuracy of STH diagnostics is the lack of a gold standard diagnostic method (42). We thus used two different approaches to estimate sensitivity and specificity of each method, consistent with prior studies.…”

Improved diagnosis of Trichuris trichiura by using a bead-beating procedure on ethanol preserved stool samples prior to DNA isolation and the performance of multiplex real-time PCR for intestinal parasites

“…Molecular methods like real-time PCR are increasingly used in the diagnosis of intestinal helminths (Verweij and Stensvold, 2014; O'Connell and Nutman, 2016). However, large-scale application of DNA detection procedures seems to be impaired, partly by the fact that the standard DNA extraction methods are not sufficient to release DNA from T. trichiura eggs (Demeler et al 2013).…”

Prospects for elimination of soil-transmitted helminths

“…Microscopy-based diagnostic methods are not sensitive at low intensity [73,74] and given that prevalence of infection is highly correlated with infection intensity, mean intensity is expected to be extremely low as populations approach the transmission breakpoint [2] and current microscopic methods would likely be inadequate for the documentation of transmission interruption. Although the assessment of novel diagnostics for STH is somewhat hampered by the lack of a gold standard [75], in field-based studies, quantitative polymerase chain reaction (qPCR) consistently detects more infections than microscopy-based methods. Using PCR as a pseudogold standard, these studies have found sensitivity of two-stool two-slide Kato-Katz as low as 70% for Ascaris and 32% for N. americanus relative to multiparallel qPCR [73], whereas sensitivity of sodium nitrate flotation was 83% for Ascaris and 34% for hookworm relative to multiplex PCR [73,76].…”