MORE THAN JUST A SYRINGE

Ticks are obligate hematophagous parasites and pathogen vectors responsible for morbidity and mortality worldwide. Ixodes scapularis is a vector for at least seven pathogens relevant to human health, including the Lyme disease microbe, Borrelia burgdorferi, and the causative agent of anaplasmosis, Anaplasma phagocytophilum. The persistence and spread of tick-borne pathogens are dependent upon interactions between ticks and host species, including the host response to the tick. In some hosts, repeated tick infestation can elicit an immune response directed against ticks which can lead to rejection and/or death of the tick. This phenomenon is termed acquired tick resistance (ATR). ATR research has traditionally relied upon artificial tick-host pairings, such as guinea pigs, which exhibit robust ATR to repeated I. scapularis infestations with aberrant or exaggerated immune responses. In contrast, I. scapularis nymphs do not elicit tick resistance in their native reservoir host, Peromyscus leucopus, contributing to the assumption that ticks do not provoke tick resistance in native hosts. However, much of the work on the ATR response to I. scapularis has been performed with nymphal ticks, with few experiments focusing on larvae. The responses of natural hosts and laboratory model hosts to repeated larval infestation has yet to be fully characterized. Additionally, the impact of host response on pathogen acquisition by larvae in native tick-host pairings has yet to be elucidated. Here, we discovered that P. leucopus mice mount an immune response with repeated I. scapularis larval infestation characterized by increasingly severe inflammation at tick bite and decreased larval feeding success. Moreover, the ATR response leads to increased ingestion of B. burgdorferi and A. phagocytophilum by feeding larvae. Our findings demonstrate that the host response to tick feeding is dependent on life stage. Characterization of ATR in a native host expands our understanding of the interactions between ticks and host species that influence pathogen maintenance and circulation in wild vertebrate and tick populations.