Patterns of antibody responses against Rocky Mountain wood tick (Dermacentor andersoni) among cattle herds in the northwestern United States

The Rocky Mountain Wood Tick, Dermacentor andersoni, is a common tick species in the western United States that transmits the rickettsial pathogen Anaplasma marginale, causing severe anemia, morbidity and mortality in cattle. Little is known about the ability of cattle to develop immunological defenses against ticks, or the potential for anti-tick immune responses to affect transmission of pathogens among cattle. Following controlled experiments that demonstrated cattle acquire immunological resistance to D. andersoni, we developed an enzyme-linked immunosorbent assay (ELISA) to screen for the presence of anti-tick antibodies among cattle in the field. Cattle from four herds located in Asotin Creek, WA; Baker City, OR; Stevensville, MT; and Tonasket, WA that represented different levels of infection with A. marginale were screened for anti-tick antibodies. The anti-tick seroprevalence values were compared to known tick densities from each location, and Anaplasma infection status of the cattle, to test if there was an association between anti-tick antibodies and tick density, or rickettsial infection. We observed a negative association between anti-tick seroprevalence and tick density in the subsequent year. Based on laboratory studies, these data suggest higher proportions of cattle with anti-tick immunity in the field may reduce tick fecundity over time. We did not observe any association between anti-tick seroprevalence and infection with Anaplasma. These data reveal it is possible to detect anti-tick antibodies in cattle outside of a laboratory environment, and suggest the immune response in cattle might have a negative affect on tick development while having little to no affect on Anaplasma infection.