The Effect of Cowpox Virus Infection on Fecundity in Bank Voles and Wood Mice (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.
Epidemiology and Infection, 2009
SUMMARYRecent studies have provided evidence that endemic pathogens may affect dynamics in animals. However, such studies have not typically considered that infected individuals might have a preceding underlying poor condition. We examined whether individuals in poor condition are more likely to become infected by an endemic pathogen, using as a system the dynamics of cowpox virus in field voles. With data from monthly sampled vole populations, a nested case-control study evaluated whether susceptible individuals with poorer condition had higher probabilities of contracting cowpox. The influence of condition was found to be considerable, especially for males. At times when a susceptible male with good body condition had a relatively low probability of becoming infected, a susceptible male with poor body condition was twice as likely to contract cowpox; if this male was also anaemic, the chances were almost quadrupled. We discuss the care needed when interpreting the findings of wild...
Rodents, cowpox virus and islands: densities, numbers and thresholds
Journal of Animal Ecology, 2003
The population dynamics of bank voles and wood mice, and of cowpox virus infection in these two species, was studied over a 2-year period in a mainland population and in 14 nearby island populations of varying sizes. 2. For both species, there was no intrinsic variation in the pattern of host dynamics with island size: small island populations behaved as though they were small subsamples of a larger population, displaying no more than the expected random variation from the general pattern. 3. None the less, the relative numbers of bank voles to wood mice increased markedly with decreasing island size; and bank vole densities tended to be higher on smaller islands. 4. Only 22 animals were discovered to have moved either between islands or between the mainland and the islands, out of 1883 captured in all. None the less, it was apparent that males were more likely to move than females. 5. Overall patterns of cowpox virus dynamics were similar in all cases. However, on all islands there were extended periods when cowpox virus infection was apparently absent, and on the small islands the numbers of infected individuals were mostly very low and in many cases infection was never found. 6. For both host species, there was no evidence for a threshold population size for cowpox virus (critical community size) in terms of density, but clear evidence for one in terms of the numerical size of populations. This suggests little support for density-dependent transmission, despite this having been the usual default assumption for non-sexually transmitted infections. 7. There was also evidence for a separate invasion threshold (between ecological and epidemiological invasion) and persistence threshold (between epidemiological invasion and persistence). This is contrary to the output of the most-quoted (deterministic) models -persistence and invasion threshold one and the same -highlighting the fact that little attention has been paid in the past to the practical meaning of the theoretical concept of a threshold. 8. In the case of the wood mice, a superficial similarity to the bank vole thresholds was potentially misleading. Wood mouse thresholds were influenced at least as much by the bank vole thresholds as they were by the dynamics within the wood mouse populations themselves. islands and in Manor Wood (notional (grid) area 10 4 m 2 ), plotted against density (mean minimum number alive per sample per 10 4 m 2 ), numbers (log (mean MNA) + (1), and area (log area (in units of10 4 m 2 ) + (2). Large islands and Manor Wood are indicated by squares; small islands by triangles.
Patterns of orthopox virus wild rodent hosts in South Germany
Vector borne and zoonotic diseases (Larchmont, N.Y.), 2009
Although cowpox virus (CPXV) infections in a variety of dead-end hosts have been investigated in Germany for more than 50 years, data on species and geographical distribution of CPXV in reservoir hosts are sparse. Here we present the first comprehensive study of 825 rodents that have been collected in Bavaria, Southern Germany. In summary, six different rodent species (Apodemus flavicollis, Myodes glareolus, Microtus arvalis, Apodemus sylvaticus, Microtus agrestis, and Arvicola amphibius) were trapped at three main trapping sites and investigated using a serum neutralization test (SNT). Prevalence of orthopox virus (OPV)-neutralizing antibodies was (with exception of one trapping site) highest in bank voles, ranging from 24.5% to 42.4%; often with SNT titers !96. Two up to 25% of yellow-necked mice were OPV sero-positive, but wood mice only at one site with 5.5%. Up to 7.7% of common voles were found to be OPV seroreactive, while M. agrestis and A. amphibius only sporadically showed seroreactivity. Further analyses of a subset of 450 bank voles and yellow-necked mice trapped at one site over a 18-month period revealed that male yellow-necked mice and female gravid yellow-necked mice had significantly more OPV-neutralizing antibodies. Mean body weight and OPV-seroreactivity were significantly negatively associated in male A. flavicollis. This was not due to shorter body length or smaller body mass index, but previously OPV-infected male A. flavicollis had dramatically reduced mean kidney weights. Seroreactivity in female bank voles was positively related to lung weights. We also found that both male yellow-necked mice and male bank voles with positive SNT titers had higher infestation rates with ectoparasites. We here show for the first time that A. flavicollis beside M. glareolus is a hypothetic host for CPXV, and that there are big geographical and spatial variations concerning the seroprevalence in rodent populations in South Germany.
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.