Trichomonosis in Austrian Songbirds—Geographic Distribution, Pathological Lesions and Genetic Characterization over Nine Years

SIMPLE SUMMARY: There are many causes of mortality in free-living songbirds, and, usually, the general public is not particularly interested in these issues. Only when large numbers of dead birds are observed within small geographic areas and within a short period of time is some public attention focused on these phenomena. In this study, we investigated episodes of mass mortality of songbirds, especially in greenfinches all over Austria, which occurred between 2012 and 2020. We noticed that all of these losses were caused by a particular protozoal parasite (Trichomonas (T.) gallinae) which induced severe inflammation of the upper digestive tract and subsequently death due to starvation. We were able to establish clear links with almost identical disease outbreaks in other countries and thus trace the path of the pathogen through Europe. It could be shown that T. gallinae has spread over the whole of Austria in recent years and occurred in many different songbird species, with a preference for greenfinches, leading to a significant decline in the population of this bird species. Since most birds are presumably infected at feeding sites, hygiene conditions and the correct selection of feeders play an important role in the prevention of disease. ABSTRACT: In the early summer of 2012, sudden mass mortality among songbirds, particularly in greenfinches (Chloris chloris, syn: Carduelis chloris) was observed in Austria, which was caused by the protozoan parasite Trichomonas gallinae. This pathogen induced fibrinonecrotic ingluvitis and/or esophagitis, leading to impairment of food intake and ultimately death due to starvation. The pathogen was successfully detected within the lesions by polymerase chain reaction (PCR) and chromogenic in situ hybridization. The epizootic resulted in a significant decline in the Austrian greenfinch population. Continuing passive surveillance in the subsequent years (2013–2020) revealed that the condition occurred each year and was present in the entire country. Genetic characterization of the pathogen showed the presence of an identical strain irrespective of geographical location, bird species, and year.