Vector-borne pathogens account for nearly 20% of all infectious disease cases worldwide. In the United States, Lyme borreliosis is the most common vector-borne pathogen and is spread by ticks of the genus Ixodes. A lesser known group of vector-borne pathogens belong to the genus Bartonella. Bartonella are transmitted to humans through numerous vectors including: fleas, lice, and to a lesser known extent ticks. Vectors must first acquire pathogens from a reservoir before they can transmit them. While the white-footed mouse is well established as a reservoir of Borrelia burgdorferi, Lyme borreliosis occurs outside of the range of the white-footed mouse. Similarly, small mammal reservoirs of Bartonella spp. are poorly understood in much of the United States. This study sought to identify the presence and prevalence of arthropod-borne pathogens among prairie rodents in northern Illinois, as well as assess the degree of coinfection within potential reservoir species. Rodents were live trapped during the summers of 2015-2017. Upon initial capture, animals were identified to species and a tissue sample was collected. DNA was extracted from tissues and screened for both Borrelia burgdorferi and Bartonella spp. using separate multi-locus sequence typing protocols. Prevalences were compared among species and coinfection rates were also analyzed.
Results/Conclusions
A total of 680 rodents were trapped between 2015 and 2017. These represented four rodent species: Ictidomys tridecemlineatus, Microtus ochrogaster, Microtus pennsylvanicus, and Zapus hudsonius. Over 30% of rodents tested were positive for Borrelia burgdorferi sensu stricto. Rates ranged from 26.6% in Z. hudsonius to 37.5% in M. pennsylvanicus with a significant difference in infection rate among species (p=0.03). All Bartonella spp. identified in this study were known pathogens. Bartonella washoensis was identified in 39.4% of I. tridecemlineatus. Bartonella grahamii was identified in 21.59% of Z. hudsonius and 18.91% of M. ochrogaster. A total of 17.65% of M. pennsylvanicus were infected with either B. grahamii or B. vinsonii. At the community level, 16.38% of tested animals were co-infected with both B. burgdorferi and a pathogenic Bartonella, which was significantly more than expected by chance (OR 1.88; CI: 1.05-3.36; p=0.038). These data suggest that several prairie dependent rodent species may represent reservoirs of Borrelia burgdorferi and pathogenic Bartonella species. Additionally, infection with one pathogen seems to increase the likelihood of infection with additional pathogens. Tick transfection experiments are needed to verify reservoir status of species involved.