Emerging Evidence of Hybrid Schistosome Parasites Spurs Calls for Improved Diagnostic Techniques

Researchers from the Liverpool School of Tropical Medicine (LSTM) alongside colleagues in Malawi have uncovered critical findings revealing the presence of zoonotic hybrid schistosome species infecting humans. These discoveries raise significant concerns about the current methods used for diagnosing schistosomiasis and understanding its true prevalence.

The recent study, published in CDC's Emerging Infectious Diseases, reports cases of mixed intestinal and urogenital schistosomiasis among patients in Malawi's Mangochi District. Notably, while standard urine-based diagnostic tests confirmed human urogenital schistosomiasis, fecal analysis revealed numerous hybrid parasite eggs. These eggs originated from crosses between Schistosoma haematobium and S. mattheei, a parasite typically infecting livestock, as well as evidence of hybridization between S. mattheei and S. mansoni, which normally causes intestinal schistosomiasis.

The findings highlight the growing complexity of schistosomiasis transmission, likely influenced by environmental changes and overlapping habitats of snail intermediate hosts that facilitate cross-species hybridization. Importantly, since zoonotic hybrid eggs were predominantly detected in fecal samples, relying solely on urine tests risks missing intestinal infections caused by these hybrids.

Dr. Angus O'Ferrall, lead author, emphasized that the World Health Organization's current diagnostic recommendations, which focus on urine sampling to map intestinal disease, may be too narrow. "The discovery of hybrid eggs in intestinal tracts suggests we might be underestimating infections, especially those caused by zoonotic hybrids."

The study advocates for expanded surveillance strategies that include routine examination of fecal samples alongside urine tests, along with utilizing molecular identification tools capable of detecting hybrid species. Such measures are vital for accurate diagnosis, effective treatment, and better disease control.

Professor Russell Stothard, heading the HUGS Project at LSTM, pointed out that understanding schistosome genomics necessitates an adaptation of field tools and public health policies. Hybrid parasites present tangible challenges to control programs, particularly in settings where humans and animals regularly interact.

Ultimately, further research is necessary to assess the prevalence of zoonotic and hybrid schistosomes in endemic areas like Malawi, and to understand their impact on disease burden and efforts to control schistosomiasis.

Source: https://medicalxpress.com/news/2025-05-hybrid-schistosome-parasites-diagnostic-methods.html