A longitudinal study of an endemic disease in its wildlife reservoir: cowpox and wild rodents (original) (raw)
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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...
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 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.
Orthopox Virus Infections in Eurasian Wild Rodents
Vector-Borne and Zoonotic Diseases, 2011
The genus Orthopoxvirus includes variola (smallpox) virus and zoonotic cowpox virus (CPXV). All orthopoxviruses (OPV) are serologically cross-reactive and cross-protective, and after the cessation of smallpox vaccination, CPXV and other OPV infections represent an emerging threat to human health. In this respect CPXV, with its reservoir in asymptomatically infected wild rodents, is of special importance. In Europe, clinical cowpox has been diagnosed in both humans and animals. The main objective of this study was to elucidate the prevalence of OPV infections in wild rodents in different parts of Eurasia and to compare the performance of three real-time polymerase chain reaction (PCR) methods in detecting OPV DNA in wildlife samples. We investigated 962 wild rodents from Northern Europe (Finland), Central Europe (Germany), and Northern Asia (Siberia, Russia) for the presence of OPV antibodies. According to a CPXV antigen-based immunofluorescence assay, animals from 13 of the 17 locations (76%) showed antibodies. Mean seroprevalence was 33% in Finland (variation between locations 0%-69%), 32% in Germany (0%-43%), and 3.2% (0%-15%) in Siberia. We further screened tissue samples from 513 of the rodents for OPV DNA using up to three real-time PCRs. Three rodents from two German and one Finnish location were OPV DNA positive. The amplicons were 96% to 100% identical to available CPXV sequences. Further, we demonstrated OPV infections as far east as the Baikal region and occurring in hamster and two other rodent species, ones previously unnoticed as possible reservoir hosts. Based on serological and PCR findings, Eurasian wild rodents are frequently but nonpersistently infected with OPVs. Results from three real-time PCR methods were highly concordant. This study extends the geographic range and wildlife species diversity in which OPV (or CPXV) viruses are naturally circulating.
Serologic Survey of Orthopoxvirus Infection Among Rodents in Hungary
Vector-Borne and Zoonotic Diseases, 2015
As a result of discontinuing vaccination against smallpox after the late 1970s, different orthopoxviruses (OPVs), such as cowpox virus (CPXV), have become a re-emerging healthcare threat among zoonotic pathogens. In Hungary, data on OPV prevalence among its rodent host species have been absent. Here, rodents belonging to four species, i.e., striped field mouse (Apodemus agrarius), yellow-necked mouse (A. flavicollis), wood mouse (A. sylvaticus) and bank vole (Myodes glareolus), were live trapped at 13 sampling plots on a 149-ha area in the Mecsek Mountains, Hungary, from March to September in 2011 and 2012. Rodent sera were collected and screened for OPV-reactive antibodies with an immunfluorescence assay (IFA). Among the 1587 tested rodents, 286 (18.0%) harbored OPV-specific antibodies. Seroprevalence was the highest for the bank vole (71.4%) and the striped field mouse (66.7%). Due to a masting event in the autumn of 2011 across Central Europe, the abundance of bank voles increased drastically in the 2012 season, raising the overall OPV seroprevalence. We provide the first data on OPV occurrence and seroprevalence in rodents in Hungary. The circulation of OPV in rodents in densely populated areas warrants further studies to elucidate the zoonotic potential of OPV in humans.
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.
Proceedings of the Royal Society B: Biological Sciences, 2006
There have been virtually no studies of 'who acquires infection from whom' in wildlife populations, but patterns of transmission within and between different classes of host are likely to be reflected in the spatiotemporal distribution of infection among those host classes. Here, we use a modified form of K-function analysis to test for space-time interaction among bank voles and wood mice infectious with cowpox virus. There was no evidence for transmission between the two host species, supporting previous evidence that they act as separate reservoirs for cowpox. Among wood mice, results suggested that transmission took place primarily between individuals of the opposite sex, raising the possibility that cowpox is sexually transmitted in this species. Results for bank voles indicated that infected females might be a more important source of infection to either sex than are males. The suggestion of different modes of transmission in the two species is itself consistent with the apparent absence of transmission between species.