Abstract
Seasonal variations in individual contacts give rise to a complex interplay between host demography and pathogen transmission. This is particularly true for wild populations, which highly depend on their natural habitat. These seasonal cycles induce variations in pathogen transmission. The seasonality of these biological processes should therefore be considered to better represent and predict pathogen spread. In this study, we sought to better understand how the seasonality of both the demography and social contacts of a mountain ungulate population impacts the spread of a pestivirus within, and the dynamics of, this population. We propose a mathematical model to represent this complex biological system. The pestivirus can be transmitted both horizontally through direct contact and vertically in utero. Vertical transmission leads to abortion or to the birth of persistently infected animals with a short life expectancy. Horizontal transmission involves a complex dynamics because of seasonal variations in contact among sexes and age classes. We performed a sensitivity analysis that identified transmission rates and disease-related mortality as key parameters. We then used data from a long-term demographic and epidemiological survey of the studied population to estimate these mostly unknown epidemiological parameters. Our model adequately represents the system dynamics, observations and model predictions showing similar seasonal patterns. We show that the virus has a significant impact on population dynamics, and that persistently infected animals play a major role in the epidemic dynamics. Modeling the seasonal dynamics allowed us to obtain realistic prediction and to identify key parameters of transmission.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-015-0218-8) contains supplementary material, which is available to authorized users.
Highlights
Pathogen spread in both human and animal populations is largely constrained by seasonal variations in individual contacts [1]
We considered in the model five health states (Figure 1): S0, kids protected by maternal antibodies, S, susceptible to infection, T, transiently infected, R, resistant, and P, persistently infected
These parameters were the mortality of persistently infected (PI) animals, the risk of abortion (ρ), and the coefficient of horizontal transmission by contact with a PI animal, the latter being mostly unknown for Pyrenean chamois
Summary
Pathogen spread in both human and animal populations is largely constrained by seasonal variations in individual contacts [1]. Sexual segregation, i.e., the separation of males and females by habitat, spatially or socially outside of the breeding season, is a common phenomenon among a large range of animal species [5]. In domestic species (and probably in wild species too), pestiviruses are a significant cause of reproductive failures such as abortion and stillbirths [13] They may have immunosuppressive effects, which increase the severity of other opportunistic infections [14]. Classical swine fever occurs in domestic pigs and wild boars and causes major economic losses, in countries with an industrialized pig production sector [12,16]
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