Wild deer in the United Kingdom are a potential reservoir for the livestock parasite .

Redwater fever is an economically important disease of cattle in the United Kingdom caused by the protozoan parasite . Control efforts are dependent on accurate local historic knowledge of disease occurrence, together with an accurate appreciation of current underlying risk factors. Importantly, the involvement of red deer in the transmission of this pathogen in the UK remains unclear. We employed a polymerase chain reaction approach combined with DNA sequencing to investigate infections in livestock and red deer at a UK farm with a history of tick-borne disease. This revealed several -infected cattle that were not displaying overt clinical signs. Additionally, 11% of red deer on the farmland and surrounding areas were infected with this parasite. We also found that 16% of the red deer were infected with , the first time this parasite has been detected in the UK. The finding of in the red deer population updates our knowledge of epidemiology in the UK and has implications for the effective control of redwater fever.