Prior Infection Induces Long-Lasting Partial Immunity to Reduce Transmission within Flocks in an Avian Host-Pathogen...

AbstractPopulation-level differences in the ability to maintain immunity can lead to contrasting survival outcomes between groups and determine how future outbreaks will spread. Pathology and infectiousness during subsequent infections can be influenced by immunity and an increase in resistance or tolerance of individuals. However, determining the longevity and effectiveness of immunity in a wildlife population is challenging because of the lack of infrastructure for long-term monitoring of populations and individuals and for host-pathogen-specific tests. Furthermore, predicting wildlife disease dynamics requires an understanding of individual-level heterogeneity in pathology and behavior, as well as a knowledge of how populations with differing partial immunity will transmit disease, which is currently limited. Using an avian host-pathogen system, we ran two experiments to determine whether previously exposed birds had immunity to Mycoplasma gallisepticum (MG) after 3 yr and whether MG transmission differed between first- and second-infection index birds. Birds retained partial immunity to MG for 3 yr after their original infection and showed signs of being resistant to infection. The transmission experiment revealed that although first- and second-infection index birds experienced pathology and pathogen growth, only first-infection birds transmitted MG. Here, 3 yr could represent lifetime protection for individuals who survive their first infection and a reduction in risk for other members of their flock. Our research has important implications for understanding MG epidemics in wild populations of birds and disease in wildlife more broadly.