Infection of Cytauxzoon felis in domestic cats produces a severe disease characterised by fever, lethargy, inappetence, anorexia, depression, dehydration, icterus and often death. Transmission of C. felis to cats is dependent on being fed upon by infected Amblyomma americanum (lone star ticks). The purpose of the present study was to determine if application of a 10 % imidacloprid/4.5 % flumethrin collar (Seresto®, Bayer) on cats prevents transmission of C. felis by repelling ticks. Twenty cats were randomised to either a treated (n = 10) or non-treated control group (n = 10) based on their susceptibility to ticks. Cats of high, medium and low tick susceptibility were represented in both groups. Treated cats were fitted with 10 % imidacloprid/4.5 % flumethrin collars on study day 0 and both groups were then infested with C. felis-infected A. americanum on study day 30. Tick thumb counts were performed at 24 and 48 hours post infestation. Transmission of C. felis was determined by examining blood of cats by DNA extraction followed by PCR amplification with piroplasm-specific primers. Ticks did not attach to any of the 10 % imidacloprid/4.5 % flumethrin- treated cats. However, ticks attached and fed on all the non-treated control cats. The geometric mean number of ticks attached to the non-treated control cats at 24 and 48 hours was 15.3 and 14.2, respectively. Cytauxzoon felis was transmitted to 9 of 10 (90 %) non-treated control cats; C. felis was not transmitted to any of the treated cats. Transmission of C. felis to the non-treated cats was first detected between 8 and 16 days post infestation. Our results indicate that application of the 10 % imidacloprid/4.5 % flumethrin collar to cats prevented ticks from attaching, feeding and transmitting C. felis.