CATTADORI, Isabella M; Penn State University: The effect of immunity and seasonality on pattern of infection

Insight into the dynamics of parasite-host relationships of higher vertebrates requires an understanding of two important features: the nature of transmission and the development of acquired immunity in the host. We have examined the dynamics of infection of two gastrointestinal nematodes, Trichostrongylus retortaeformis and Graphidium strigosum, and the poxvirus myxoma within a natural population of rabbits sampled monthly for 26 years. Rabbit age was re-constructed using body mass, and parasites intensity and virus prevalence were recorded. The rabbit age-nematode intensity curves were examined seasonally and with and without myxoma co-infection. We found that a decrease in immunity with host age associated with seasonality in host reproduction and parasite force of infection increased the number of heavily parasitized rabbits. These heavily infected hosts also had a significant higher net parasite transmission rate. We concluded that specific groups of rabbits that became immunosupressed during part of the year are responsible for parasites persistence and transmission.