The effect of seasonal birth pulses on pathogen persistence in wild mammal populations

Abstract

The notion of a critical community size (CCS), or population size that is likely to result in long-term persistence of a communicable disease, has been developed based on the empirical observations of acute immunizing infections in human populations, and extended for use in wildlife populations. Seasonal birth pulses are frequently observed in wildlife and are expected to impact infection dynamics, yet their effect on pathogen persistence and CCS have not been considered. To investigate this issue theoretically, we use stochastic epidemiological models to ask how host life-history traits and infection parameters interact to determine pathogen persistence within a closed population. We fit seasonal birth pulse models to data from diverse mammalian species in order to identify realistic parameter ranges. When varying the synchrony of the birth pulse with all other parameters being constant, our model predicted that the CCS can vary by more than two orders of magnitude. Tighter birth pulses tended to drive pathogen extinction by creating large amplitude oscillations in prevalence, especially with high demographic turnover and short infectious periods. Parameters affecting the relative timing of the epidemic and birth pulse peaks determined the intensity and direction of the effect of pre-existing immunity in the population on the pathogen's ability to persist beyond the initial epidemic following its introduction.

Biannual birth pulses allow filoviruses to persist in bat populations

“…The use of a periodic Gaussian function (PGF) that allows births to be pulsed over a period and ensures that no births occur outside the birthing season has previously been described [23]. The function looks like…”

“…A full exploration of the function and general effects of synchronous birthing on infection maintenance is described elsewhere [23].…”

“…Host traits, such as maternally derived antibody [20,21] and seasonal birthing [22,23], can affect infection dynamics within populations. Theoretical studies using stochastic epidemiological models with a seasonal birth pulse suggest that increased birthing synchrony increases the necessary population size required for infection persistence (CCS) [23]. Thus, seasonal birthing may decrease the probability of pathogens persisting in a colony, but lead to periods of increased infection prevalence following birthing.…”

Timing and severity of immunizing diseases in rabbits is controlled by seasonal matching of host and pathogen dynamics

“…This is primarily because of a paucity of long-term and site-specific field data on RHD and myxomatosis epizootics and the absence (until recently) of modelling frameworks that are able to couple multi-disease epidemiological processes dynamically with stochastic -demographic models. However, understanding the timing of interactions between hosts and viruses, and how these interactions can vary in time and space owing to environmental conditions and global change [52] is crucial for both accurate prediction of the timing of epizootics and, subsequently, for understanding their impact on long-term population growth of hosts [4,53].…”

“…These are not independent, because birth and mortality determine the pool of individuals accessible to infections and infectious disease can significantly reduce host populations or the reproductive behaviour of individuals. Consequently, changes in either demographic or epidemiological traits in space and time can strongly influence coupled host-pathogen dynamics [1][2][3][4].…”