Host condition and individual risk of cowpox virus infection in natural animal populations: cause or effect? (original) (raw)
Related papers
Journal of Animal Ecology, 2008
1Cowpox virus is an endemic virus circulating in populations of wild rodents. It has been implicated as a potential cause of population cycles in field voles Microtus agrestis L., in Britain, owing to a delayed density-dependent pattern in prevalence, but its impact on field vole demographic parameters is unknown. This study tests the hypothesis that wild field voles infected with cowpox virus have a lower probability of survival than uninfected individuals.2The effect of cowpox virus infection on the probability of an individual surviving to the next month was investigated using longitudinal data collected over 2 years from four grassland sites in Kielder Forest, UK. This effect was also investigated at the population level, by examining whether infection prevalence explained temporal variation in survival rates, once other factors influencing survival had been controlled for.3Individuals with a probability of infection, P(I), of 1 at a time when base survival rate was at median levels had a 22·4% lower estimated probability of survival than uninfected individuals, whereas those with a P(I) of 0·5 had a 10·4% lower survival.4At the population level, survival rates also decreased with increasing cowpox prevalence, with lower survival rates in months of higher cowpox prevalence.5Simple matrix projection models with 28 day time steps and two stages, with 71% of voles experiencing cowpox infection in their second month of life (the average observed seroprevalence at the end of the breeding season) predict a reduction in 28-day population growth rate during the breeding season from λ = 1·62 to 1·53 for populations with no cowpox infection compared with infected populations.6This negative correlation between cowpox virus infection and field vole survival, with its potentially significant effect on population growth rate, is the first for an endemic pathogen in a cyclic population of wild rodents.Cowpox virus is an endemic virus circulating in populations of wild rodents. It has been implicated as a potential cause of population cycles in field voles Microtus agrestis L., in Britain, owing to a delayed density-dependent pattern in prevalence, but its impact on field vole demographic parameters is unknown. This study tests the hypothesis that wild field voles infected with cowpox virus have a lower probability of survival than uninfected individuals.The effect of cowpox virus infection on the probability of an individual surviving to the next month was investigated using longitudinal data collected over 2 years from four grassland sites in Kielder Forest, UK. This effect was also investigated at the population level, by examining whether infection prevalence explained temporal variation in survival rates, once other factors influencing survival had been controlled for.Individuals with a probability of infection, P(I), of 1 at a time when base survival rate was at median levels had a 22·4% lower estimated probability of survival than uninfected individuals, whereas those with a P(I) of 0·5 had a 10·4% lower survival.At the population level, survival rates also decreased with increasing cowpox prevalence, with lower survival rates in months of higher cowpox prevalence.Simple matrix projection models with 28 day time steps and two stages, with 71% of voles experiencing cowpox infection in their second month of life (the average observed seroprevalence at the end of the breeding season) predict a reduction in 28-day population growth rate during the breeding season from λ = 1·62 to 1·53 for populations with no cowpox infection compared with infected populations.This negative correlation between cowpox virus infection and field vole survival, with its potentially significant effect on population growth rate, is the first for an endemic pathogen in a cyclic population of wild rodents.
The effects of cowpox virus on survival in natural rodent populations: increases and decreases
Journal of Animal Ecology, 2002
The effect of cowpox virus on survival in two rodent hosts was investigated using nearly 4 years of longitudinal data from two sites. 2. We investigated whether an individual's probability of infection influenced the probability of surviving the next month. We also investigated the effect at the population level, examining whether, in addition to seasonal effects, changes in cowpox prevalence explained further temporal variation in survival rates. 3. In bank voles, but not wood mice, individuals with high probabilities of infection survived better than uninfected animals. 4. At the level of the population, the effect of infection on survival varied through the year in both species. Survival rates in late summer increased with cowpox prevalence, whilst survival rates in winter decreased with cowpox prevalence. 5. We discuss why parasites such as cowpox virus may increase or decrease host survival and why the effect may depend on the time of year.
The Effect of Cowpox Virus Infection on Fecundity in Bank Voles and Wood Mice
Proceedings of The Royal Society B: Biological Sciences, 1997
Although epidemic infectious diseases are a recognized cause of changes in host population dynamics, there is little direct evidence for the e¡ect of endemic infections on populations. Cowpox virus is an orthopoxvirus which is endemic in bank voles (Clethrionomys glareolus), wood mice (Apodemus sylvaticus) and ¢eld voles (Microtus agrestis) in Great Britain. It does not cause obvious signs of disease nor does it a¡ect survival, but in this study we demonstrate experimentally that it can reduce the fecundity of bank voles and wood mice by increasing the time to ¢rst litter by 20^30 days. The pathogenic mechanisms causing this e¡ect are at present not known, but this ¢nding suggests that natural subclinical infection could have a considerable e¡ect on the dynamics of wild populations.
The epidemiology of cowpox in its reservoir hosts
1999
It is generally accepted that the reservoir hosts of cowpox virus are wild rodents, although direct evidence for this is lacking for much of the virus's geographic range. Here, through a combination of serology and PCR, we demonstrate conclusively that the main hosts in Great Britain are bank voles, wood mice and short-tailed field voles. However, we also suggest that wood mice may not be able to maintain infection alone, explaining the absence of cowpox from Ireland where voles are generally not found. Infection in wild rodents varies seasonally, and this variation probably underlies the marked seasonal incidence of infection in accidental hosts such as humans and domestic cats.
Seasonal host dynamics drive the timing of recurrent epidemics in a wildlife population
Proceedings of The Royal Society B: Biological Sciences, 2009
The seasonality of recurrent epidemics has been largely neglected, especially where patterns are not driven by forces external to the population. Here, we use data on cowpox virus in field voles to explore the seasonal patterns in wildlife (variable abundance) populations and compare these with patterns previously found in humans. Timing in our system was associated with both the number and the rate of recruitment of susceptible hosts. A plentiful and sustained supply of susceptible hosts throughout the summer gave rise to a steady rise in infected hosts and a late peak. A meagre supply more limited in time was often insufficient to sustain an increase in infected hosts, leading to an early peak followed by a decline. These seasonal patterns differed from those found in humans, but the underlying association found between the timing and the supply of susceptible hosts was similar to that in humans. We also combine our data with a model to explore these differences between humans and wildlife. Model results emphasize the importance of the interplay between seasonal infection and recruitment and suggest that our empirical patterns have a relevance extending beyond our own system.
Seasonal host dynamics drive the timing of recurrent epidemics in a wildlife
2009
The seasonality of recurrent epidemics has been largely neglected, especially where patterns are not driven by forces external to the population. Here, we use data on cowpox virus in field voles to explore the seasonal patterns in wildlife (variable abundance) populations and compare these with patterns previously found in humans. Timing in our system was associated with both the number and the rate of recruitment of susceptible hosts. A plentiful and sustained supply of susceptible hosts throughout the summer gave rise to a steady rise in infected hosts and a late peak. A meagre supply more limited in time was often insufficient to sustain an increase in infected hosts, leading to an early peak followed by a decline. These seasonal patterns differed from those found in humans, but the underlying association found between the timing and the supply of susceptible hosts was similar to that in humans. We also combine our data with a model to explore these differences between humans and wildlife. Model results emphasize the importance of the interplay between seasonal infection and recruitment and suggest that our empirical patterns have a relevance extending beyond our own system.