While data on the seroprevalence of vector-transmitted pathogens in the United States are fairly extensive, there is less information about the occurrence of these diseases on the West Coast. This study examined the distribution of 4 vector-borne canine pathogens in Washington, Oregon, and California. Blood samples were collected from 2431 pet dogs visiting clinics for routine preventive examinations. Each sample was tested for Anaplasma phagocytophilum, Borrelia burgdorferi, Ehrlichia canis, and Dirofilaria immitis using the SNAP 4Dx kit (idexx.com). The overall seroprevalence was 2.4% for A phagocytophilum, 1.2% for B burgdorferi, 0.7% for E canis, and 0.7% for D immitis. The distribution maps of the data show relatively high levels of seropositive dogs in northern California, southwestern Oregon, and the Puget Sound region, with sporadic clusters of infection throughout the other western states. California had the highest levels of all pathogens, and individual counties in California had exposure ranging from 0% to 16%. The highest seroprevalence identified in the study was found in Josephine County, Oregon, where 33% of dogs tested positive for A phagocytophilum. A high rate of coinfection was also identified with both A phagocytophilum and B burgdorferi with a calculated odds ratio of 18.7.

This study fills the gap of important prevalence information for the Pacific states. Clinicians in northern California upward to the Puget Sound should be aware that these pathogens, previously thought to be largely absent from this area, are present in significant numbers. The authors also indicate that these prevalence numbers are likely underestimations caused by the seasonality of samples and the time to seroconversion following infection. Data regarding owner use of preventive treatments and dog lifestyles were not collected, so it is unclear whether these factors contributed data.—Carly Jordan, PhD

Spatial distribution of seroprevalence for Anaplasma phagocytophilum, Borrelia burgdorferi, Ehrlichia canis, and Dirofilaria immitis in dogs in Washington, Oregon, and California. Carrade D, Foley J, Sullivan M, et al. VET CLIN PATHOL 40:293-302, 2011.