Anaplasma marginale is an obligate intracellular gram-negative bacterial pathogen of ruminants. It is the etymological agent of bovine anaplasmosis, which is the most prevalent tick-borne cattle disease in the word. Despite its prevalence and severe economic impacts, few effective control measures exist for A. marginale. Antibiotic treatment, acaricide baths, and vaccines are currently used to reduce infection and attenuate disease severity, but none of these measures can completely prevent infection or eradicate the bacteria after infection of the bovine host is established. This work focuses on Rickettsia bellii, an endosymbiont of multiple species of ticks, some of which transmit A. marginale. In previously published works, our lab has shown that the presence and prevalence of R. bellii in Dermacentor andersoni affects the tick’s capacity to acquire A. marginale from infected cattle. The work presented here tests the interaction through mixed infection of D. andersoni cell culture with both A. marginale, and R. bellii. Using this approach, we identify effects of R. bellii infection on A. marginale’s capacity to establish infection in D. andersoni cells, as well as its ability to grow in host cells after infection is established. Additionally, we predict effectors secreted through the type IV secretion system of R. bellii, along with seven other species of Rickettsia from across the genus. This work leads to a better understanding of the genus Rickettsia and its strategies for host infection, as well as producing a list of candidate effectors found in R. bellii with potential associations with the attenuation of A. marginale infection observed in the mixed infection experiments. These analyses bring us closer to a mechanistic understanding of the effect of R. bellii on A. marginale infection of D. andersoni, which in turn may lead to new treatment strategies for bovine anaplasmosis through manipulation of tick vectors.