Theileria annae in a young Swedish dog

A severe regenerative anemia was detected in a 12-week-old mixed breed puppy in Sweden. A small protozoan parasite was observed in erythrocytes on a blood smear. It was initially suspected to be Babesia gibsoni based on its size and because B. gibsoni was previously recorded in Sweden. Surprisingly, specific polymerase chain reaction analysis identified the protozoan as Theileria annae. T. annae is endemic in Northwest Spain, is very uncommonly reported elsewhere and has never been recorded in Scandinavia. T. annae has been identified in dogs used for dog fighting, and it is thought to be transmitted by dog bites. This puppy was a mixed pit bull terrier. Pit bull terriers are sometimes used for dog fighting. T. annae has been reported to be transmitted vertically, and in light of the puppy's age, this transmission was suspected in the present case.