Summary
A horse erythrocyte culture technique, partly modifying that originally developed by Holman, was used to detect the presence of Theileria equi strains in 12 horse and 2 mule blood samples. The animals were placed into four groups on the basis of their case history and laboratory test results: the mules and two horses were considered as infected and included in the ‘recent infection’ group, four horses with a history of past infection were included in the ‘past infection’ group and four animals subjected to anti-theileria treatment formed the ‘treated animals’ group. The final group consisted of two horses with an unknown history of infection. Ten T. equi strains were isolated and adapted in vitro from the fourteen animals tested: nine of these originated from the horse samples and one from mule blood. This is the first time that a T. equi strain isolated from a mule has been adapted in erythrocyte cultures. All strains isolated from horses showed growth and in vitro adaptation with a parasitaemia peak of over 10%. Following freezing and reculturing, adapted strains showed growth after a quiescence period of eight days. The method proved to be effective for culturing and replicating field T. equi strains from horses and mules. The technique was also able to identify carriers of infection which were negative on microscopic examination, indirect immunofluorescence and complement fixation.

Keywords
Complement fixation, Horses, Immunofluorescence, In vitro culture, Microscopic examination, Mules, Theileria equi.