A clonal strain of Trichomonas gallinae is the aetiologic agent of an emerging avian epidemic disease

► Finch trichomonosis was diagnosed as an emerging infectious disease of British finches in 2005. ► Epidemic mortality due to this novel parasitic infection has occurred in subsequent years. ► Sequence and multilocus typing tools were used to compare parasite isolates from bird species. ► There was no evidence of heterogeneity amongst the parasites infecting British passerines. ► A clonal strain of Trichomonas gallinae is the causative agent of finch trichomonosis epidemic.