Diversity of rickettsiae in a rural community in northern California

Far northern California forests are highly biodiverse in wildlife reservoirs and arthropod vectors that may propagate rickettsial pathogens in nature. The proximity of small rural communities to these forests puts people and domestic animals at risk of vector-borne infection due to spillover from wildlife. The current study was conducted to document exposure to rickettsial pathogens in people and domestic animals in a rural community, and identify which rickettsiae are present in sylvatic and peri-domestic environments near this community. Blood samples from people, domestic animals (dogs, cats, and horses) and wild carnivores were tested for Rickettsia spp. antibodies and DNA (people and domestic animals only) by serology and real time (RT)-PCR, respectively. Ectoparasites were collected from dogs, wild carnivores and from vegetation by flagging, and tested for Rickettsia spp. DNA by RT-PCR. DNA sequencing of the rickettsial 17kDa protein gene or the ompA gene was used for species identification. Despite a seroprevalence of 3% in people, 42% in dogs, 79% in cats, 33% in gray foxes, and 83% in bobcats, RT-PCR on blood was consistently negative, likely because the sensitivity of this test is low, as Rickettsia spp. do not often circulate in high numbers in the blood. Rickettsia spp. DNA was found in four flea species collected from bobcats and Ctenocephalides felis collected from domestic dogs. All amplicons sequenced from fleas were R. felis. Ixodes pacificus collected by flagging were commonly infected with a Rickettsia sp. endosymbiont. Rickettsia rhipicephali DNA was found in Dermacentor variabilis from dogs, black bears, a gray fox, and a D. occidentalis collected by flagging. Dermacentor variabilis from dogs and black bears also contained R. montanensis DNA. Multiple Rickettsia spp. (including species with zoonotic and pathogenic potential) were found among human biting arthropod vectors of both wild and domestic carnivores and on flags. Knowledge of the diversity of Rickettsia spp. that are present within arthropod vectors to which people and domestic animals are exposed is an essential first step is making an accurate diagnosis and in better understanding the epidemiology of these potential pathogens. Within-host and vector interaction among these species may play a role in spillover into human and domestic animals.