Multiple strains of Trichomonas gallinae are widespread in reservoir hosts and environmental resources in UK farmland

Understanding transmission routes of parasites and pathogens is critical for the development of control measures and mitigation of impacts on host populations. Trichomonas gallinae is a widespread parasite in columbids worldwide, and has emerged as a lethal disease in passerines, particularly finches. The postulated transmission route from columbids to passerines via spillover at shared resources has not yet been empirically tested. Here, we screen 363 birds (261 columbids and 102 non-columbids) in the UK and France for the presence and strain identity of T. gallinae. To quantify potential environmental transmission, we also screened 51 food and water resources common in farmland, at 12 sites over a 2-year period. We isolated T. gallinae parasites from 79% of columbids, 36% of non-columbids, and 39% of environmental resources. Prevalence of the Type A strain was more than double in birds sampled at fed sites compared to those at unfed sites. Strain composition was mirrored in columbids, passerines, and shared food and water resources, providing compelling evidence that T. gallinae, especially the Type A strain, is transmitted via these shared resources. T. gallinae was isolated from high density feeding resources (where supplementary food was provided) nearly three times as often as low density resources (natural areas of seed-providing vegetation), meaning that careful management of supplementary resources has the potential to reduce T. gallinae prevalence in wild bird populations. Further work needs to test practical means of achieving this, but ensuring any supplementary feeding is provided at low density is likely to be critical to reducing parasite transmission.