Deer keds (Lipoptena fortisetosa) are hematophagous insects that parasitize various ungulates, including Hokkaido sika deer (Cervus nippon yesoensis). Although deer keds are potential vectors for several pathogens, their role in disease transmission in Japan remains unclear. This study aimed to evaluate the potential of L. fortisetosa as a vector for selected pathogens in sika deer. Blood samples were collected from 32 sika deer and 149 deer keds (64 from deer and 85 from the environment) from the Rusha area of the Shiretoko Peninsula, Hokkaido, Japan. Nested PCRs and sequencing were performed to detect 18S rRNA gene of Theileria sp. Thrivae, 16S rRNA gene of Anaplasma sp. AP-sd (AP-sd), and flagellin B gene of Borrelia sp. in deer and deer keds. In sika deer, the infection rate was 84 % for Theileria sp. Thrivae, 75 % of AP-sd, and 3 % of Borrelia sp. The prevalence in deer keds collected from deer was 62 % for Theileria sp. Thrivae, 2 % AP-sd, and 1 % Borrelia sp. No pathogens were detected in nonparasitic deer keds captured from the environment. Notably, Theileria sp. Thrivae and AP-sd were detected in deer keds collected from PCR-negative sika deer, suggesting that deer keds acquired pathogens from a previously infested host. The absence of pathogens in non-parasitized deer keds suggests that they do not play as a biological vector for the tested pathogens. This study suggests a potential role for L. fortisetosa as a mechanical vector, emphasizing the need for additional experiments, including infection studies.