Co-infection rates of black-legged ticks (Ixodes scapularis) in central Wisconsin
In the United States, reported cases of Lyme disease increased over two-fold between 2001-2016. The causative agent is the bacterium Borrelia burgdorferi, which is transmitted by the black-legged tick (Ixodes scapularis). This vector also transmits at least six additional pathogenic agents. My study focused on B. burgdorferi, Anaplasma phagocytophilum, Babesia microti, and Ehrlichia species. If the tick previously fed on a host that was co-infected, hosts may acquire multiple agents during a single blood meal. Such co-infections are poorly understood but likely to have important implications for the transmission dynamics of each infectious agent. My objective was to determine if co-infection rates of I. scapularis occur at frequencies other than predicted by infection rates of individual agents. My research focused on quantifying infection and co-infection rates at Hartman Creek State Park in central Wisconsin. This site has the vector (black-legged tick) and competent hosts (deer and multiple small mammal species) for these infectious agents. I collected nymphal and adult black-legged ticks from small mammal hosts and by flagging vegetation. Ticks were then screened using end-point PCR for the four agents. My data showed 103/253 (40.7%) of questing ticks infected with B. burgdorferi, 87/253 (34.4%) infected with A. phagocytophilum, and 24/253 (9.5%) infected with B. microti. My data also showed 50/253 (19.8%) of questing ticks were co-infected with ≥2 agents. I also found less co-infection of questing ticks with A. phagocytophilum and B. microti than predicted by chance, which suggests a negative population-level interaction between these two agents in the vector. The research outcomes will increase the knowledge of co-infection rates at this site and contribute to the growing body of knowledge on this subject, thereby positively impacting human health.
Ticks as carriers of disease