Meeting Abstract
Host immune responses can reduce parasite load (resistance) and/or mitigate damage caused by infection (tolerance). These defense strategies mediate the outcome of individual infections but also have implications for population-level processes. Hosts with high tolerance and low resistance maintain high performance despite high parasite burden, enabling these individuals to contribute disproportionately to transmission. Past exposure to parasites modifies the consequences of subsequent exposures for individuals, but how it impacts transmission is less clear. Antibody responses augment resistance upon parasite re-exposure, but whether re-exposures also impact tolerance has yet to be studied. Multiply exposed individuals may pose a greater risk to others in a population if they develop increased competence to transmit a parasite. We exposed wild-caught house sparrows (HOSP) 2x to West Nile virus (WNV) with exposures separated by a ten-day recovery period. We then quantified serum viremia and five forms of bird health and/or performance within and between exposures. We expected that both population-level resistance and tolerance would increase following a secondary exposure to WNV. Our initial findings show high variability among WNV-infected HOSP in viremia profiles and performance. In 90% of cases, viral loads exceeded the threshold for transmission to a vector. Despite a mortality rate of 70%, these individuals were infectious for between two and four days prior to death. We did not detect a significant relationship between infection intensity and performance. Further analysis will indicate whether survivors of primary infection develop increased tolerance and/or resistance to subsequent infection, and thus broadens our understanding of the role of individuals in disease dynamics in nature.
