Development and assessment of a standardized microscopy protocol for the diagnosis of male genital schistosomiasis by detection of Schistosoma haematobium eggs in human semen

Background Male genital schistosomiasis (MGS) is a neglected tropical disease defined by the presence of Schistosoma haematobium eggs or associated DNA in semen or genital and reproductive organs. Microscopy is typically utilized for diagnosis, however there is currently no standardized protocol and the vast heterogeneity in methods used may impact sensitivity. We aimed to develop an optimized, standardized protocol for semen microscopy through comparison of two sample concentration techniques (filtration and centrifugation-sedimentation) and optimize the protocol for usage in resource-constrained settings through the exploration of alternative, low-cost filters. Methods Aliquots of pooled human semen from healthy donors were spiked with known quantities of S. haematobium eggs (range: 1–20) and were assigned to either centrifugation or filtration. Phosphate buffered saline (PBS) was added to semen prior to filtration. Slides were examined under a microscope and egg counts recorded. The limit of detection for each method was calculated using probit analysis. Bias-reduced logistic regression was used to evaluate the association between sample concentration method and egg detection. Several types of commercially available coffee filters were investigated as potential alternatives to commercial polycarbonate filters and were assessed descriptively for their ability to trap eggs and facilitate visualization. Results The limit of detection for semen microscopy with filtration was two eggs (95% CI: 1–2 eggs), while the limit of detection for centrifugation was six eggs (95% CI: 5–7 eggs) (per 0.5 mL sample). Filtration was observed to have higher sensitivity compared to centrifugation (96.4% [95% CI: 87.7–99.6] versus 75.0% [95% CI: 61.6–85.6]), and had greater odds of detection (OR 10.6 [95% CI 2.4–46.7], p = 0.002). Each of the three coffee filter types tested and descriptively assessed were able to be utilized to filter semen samples and trap and visualize S. haematobium eggs. Conclusion The analytical sensitivity of semen microscopy for the detection of S. haematobium eggs is highly dependent on the sample concentration method and processing procedures. Filtration presents a promising opportunity for diagnosis of MGS in resource constrained settings due to its high sensitivity and low equipment requirements, particularly when used alongside accessible and low-cost alternative filters such as coffee filters.