Hybrid schistosomes threaten disease control in Africa

Hybrid parasites are undermining efforts to control schistosomiasis, one of the world’s most widespread neglected diseases, according to new research led by the Liverpool School of Tropical Medicine (LSTM). The findings, published in a Special Issue of Philosophical Transactions B (Royal Society), reveal that parasite hybridisation is far more common than previously thought - with implications for disease spread in Africa and beyond.

Schistosomiasis, caused by waterborne schistosome parasites, affects over 200 million people worldwide, leading to chronic illness, disability, and, in severe cases, life-threatening organ damage. Despite decades of mass drug administration programmes, transmission persists, especially in communities dependent on freshwater for daily life.

The new collection of 12 multidisciplinary studies shows that hybrids form when different parasite species mix in shared freshwater environments, including those infecting humans and livestock. Some hybrid parasites display altered traits, such as higher virulence, a broader host range, and greater transmission potential. These changes can complicate diagnosis and mean that current control measures - focused mainly on human infection - may miss key reservoirs of disease.

Professor Russell Stothard, senior author and co-editor of the Special Issue, said:

"Schistosomes are showing evolution in action with remarkable speed. Hybrid parasites are no longer rare outliers - they are reshaping the epidemiological landscape and challenging existing surveillance and control strategies."

Evidence from the studies highlights new hybrid variants emerging across northern and southern Africa. For example, Schistosoma haematobium × S. mattheei, a hybrid linking human- and livestock-infecting species, is now a common cause of genital schistosomiasis in parts of Malawi, underscoring the blurred boundaries between human and animal health.

Professor Janelisa Musaya, Associate Director at the Malawi Liverpool Wellcome Programme (MLW), added:

"Persistent infections in areas where humans and livestock coexist have long puzzled us. These landmark studies reveal that hybridisation complicates elimination efforts and call for a One Health approach integrating human, animal, and environmental health."

The research highlights the urgent need for improved surveillance, including genetic monitoring, to track hybrid schistosomes and inform control strategies. Without these measures, hybrid parasites could slow or even reverse progress toward elimination targets.

Five of the papers included in the special issue are led by LSTM scientists, with several arising from the Wellcome-funded HUGS project, a collaboration between Liverpool School of Tropical Medicine and the Malawi Liverpool Wellcome Programme.

More information online

1. The Special Issue, Parasite evolution and impact in action: Exploring the importance and control of hybrid schistosomes in Africa and beyond published by the Royal Society