Occurrence and characterisation of Toxoplasma gondii infection in free-living Eurasian beavers, Castor fiber, from southern England.

Toxoplasma gondii is a globally distributed apicomplexan protozoan of zoonotic importance. Domestic cats (Felis catus) and related felids constitute its sole definitive hosts, while numerous warm-blooded species serve as intermediate hosts. Infection outcomes for intermediate hosts range from latent toxoplasmosis to behaviour alteration and fatal systemic disease. Oocysts, the lifecycle environmental stage, are often washed into watercourses, making river-dwelling species like Eurasian beavers (Castor fiber) particularly at risk. To investigate the presence and impact of T. gondii on beavers in the United Kingdom, archived brain, heart, and liver from 23 beavers necropsied between 2021 and 2023 were screened for T. gondii DNA by nested- and quantitative PCR. Positive samples were genotyped using a panel of six published PCR-Restriction Fragment Length Polymorphism (PCR-RFLP) assays and amplicon sequencing. Sequences were aligned with those reported previously from UK and other wildlife species to assess the occurrence of shared genotypes. Toxoplasma gondii DNA was detected in 19/23 (83%) Eurasian beavers; all consistent with PCR-RFLP ToxoDB#3 with limited genetic diversity, concurring with findings from previous surveillance of UK wildlife species. Following histopathological screening non-suppurative toxoplasmosis was characterised in 3/6 tissues selected from two animals. These results demonstrate a high occurrence of T. gondii infection in UK beavers.