COMPLETED PROJECTS
Genetic Relatedness of Free-Ranging White-tailed Deer Related to Transmission of Chronic Wasting Disease in Wisconsin
Investigator: Michael D. Samuel, USGS, University of Wisconsin-Madison,
Funding: Wisconsin Department of Natural Resources
Expected Completion: June 30, 2007
CWD was first detected in Wisconsin in three deer harvested during the 2001 fall hunting season. The source of CWD infections in Wisconsin is unknown and will likely remain unknown. However, we suspect that CWD has been present in the Wisconsin deer herd for at least 10 years. Very little is known about the routes of CWD transmission between free-ranging animals, the rates of infection, or how disease spreads within a local population. Routes of direct transmission of CWD among white-tailed deer will likely be related to the degree of social and behavioral interactions that occur in free-ranging animals. The intensity of these interactions varies depending on age/sex relationships and genetic relationships among deer. Due to social structure, genetically related adult female white-tailed deer are not randomly distributed across the landscape. Purdue et al. (2000) found that populations of white-tailed deer separated by >25 km shared very few maternally inherited mitochondrial DNA markers and had different frequencies of biparentally inherited DNA markers. Based on alleles and genotypes of a single DNA locus Scribner et al. (1997) found that white-tailed deer in an 800 km2 area of Georgia formed genetic clusters. Matthews and Porter (1993) correlated genetic clusters with matrilineal social groups that were defined by radiotelemetry data.
The general objectives of this study are to characterize the spatial genetic structuring and degree of genetic relatedness among free-ranging white-tailed deer in the CWD affected area in south-central Wisconsin. Relatedness of deer will be used to evaluate prevalence of CWD, transmission dynamics within and among related deer, genes flow related to landscape feature, or genetic resistance of deer to CWD. This research project will provide supplementary genetic information to assist the evaluation of previously funded research studies.
Serological Survey of WNV Exposure in Mammalian Scavengers in the CWD Eradication Zone
Investigator: Michael D. Samuel, USGS, University of Wisconsin-Madison
Funding: Wisconsin Department of Health and Family Services
Expected Completion: January 31, 2007
Although West Nile Virus (WNV) is known to infect over 58 species of mosquitoes and 284 avian species, with few exceptions little is known about its role in the cause and transmission of disease in mammalian species. Besides humans and horses, incidental cases of WNV exposure based on serological evidence have been reported in a handful of mammals such as bats, rabbits, and in sensational species such as bears, wolves, reindeer and even Barbary Macaques. In certain mammals, for example squirrels, mortality due to WNV has also been reported. For most of these species, the role of infection in the transmission of WNV is largely unknown. The objective of this research is to gain a better understanding of the incidence of WNV infection in native meso-predators during the next two years. By extending our analysis of trapped animals collected for a companion study on Chronic Wasting Disease for two more seasons, we can determine whether the elevated incidence in 2003-2004 was a result of short-term environmental conditions or an indication of a long-term transmission mechanism. In addition, we can also estimate annual changes in WNV exposure and correlate these results with transmission information from mosquito collections and human cases. Our project will continue to rely on serum samples collected at necropsy on Nobuto strips and the presence and titer of neutralizing antibodies for WNV will be performed by PRNT. Our goal is to sample around 100 animals each year from each of the following species: opossum, raccoon, and coyote, and to perform incidental testing of red fox, skunk, and feral cats as available.
Development of Epizootiologic Models and Related Analytical Support for Chronic Wasting Disease in Wisconsin White-tailed Deer and Other Cervids
Investigator: Michael D. Samuel, USGS, University of Wisconsin-Madison
Funding: U.S. Geological Survey, Wisconsin Department of Natural Resources
Expected Completion: June 30, 2007
The spread of CWD in wild animals is of great concern. The disease was originally described in captive animals 35 years ago in Colorado. However, over the last five years, CWD has been detected in wild cervids in several surrounding states and Canada. In early 2002, CWD was detected in wild deer in South Dakota, Wisconsin, and now in New Mexico. The recent detection of CWD in the wild white-tailed deer herd in Wisconsin is of particular concern. White-tailed deer appear more susceptible than mule deer and elk to CWD with a greater percentage of the herd becoming infected. Until now, CWD was found in white-tailed deer herds in Colorado, Wyoming, and Nebraska where deer occur at densities of approximately 2-5 deer per square mile. In contrast in Wisconsin, deer are found at 50+ animals per square mile. No one knows how rapidly CWD will spread among white-tailed deer at these densities or what long-term affect this disease will have on a herd of this size (approximately 1.5 million animals).
The objectives of research are: (1) develop strategic and spatially explicit epidemiological models of CWD involving white-tailed deer in Wisconsin and in collaboration with other research studies test and improve these models; (2) in collaboration with other research projects, extend, test, and improve these epidemiological models to incorporate features of CWD found in wild cervids from endemic areas; (3) extend these models to incorporate epidemiology and ecology applicable in the event of TB or FMD outbreaks; and (4) provide statistical and quantitative epidemiological support to the National Wildlife Health Center and the Wisconsin Department of Natural Resources (WDNR) to assist in the evaluation of CWD surveillance, monitoring, and research efforts in Wisconsin.
Disease Patterns in the CWD Eradication Zone
Investigator: Michael D. Samuel, USGS, University of Wisconsin-Madison
Funding: U.S. Geological Survey
Expected Completion: December 31, 2006
Since the discovery of CWD in southern Wisconsin in 2001, more than 20,000 deer have been removed from a >2,500 km2 disease eradication zone surrounding the three initial cases. Nearly all deer removed were tested for CWD infection and sex, age, and harvest location were recorded. Our analysis used data from a 310 km2 core study area where disease prevalence was higher than surrounding areas. We found no difference in harvest rates between CWD infected and non-infected deer. Our results show that the probability of infection increased with age and that adult males were more likely to be infected than adult females. Six fawns tested positive for CWD, five fawns from the core study area, including the youngest (5 months) free-ranging cervid to test positive. The increase in male prevalence with age is nearly twice the increase found in females. We concluded that CWD is not randomly distributed among deer and that differential transmission among sex and age classes is likely driving the observed patterns in disease prevalence. Understanding CWD transmission in free-ranging cervid populations will be essential to the development of strategies to manage this disease in areas where CWD is found as well as for surveillance strategies in areas where CWD threatens to spread.
We also evaluated the hypothesis of socially facilitated transmission of chronic wasting disease (CWD) among adult female white-tailed deer using spatial location and genetic relatedness for 1,387 female deer, as well as the spatial location of 1,321 adult male deer harvested during 2002-2004 CWD control efforts in Wisconsin, USA. There was little correlation between genetic relatedness and geographic distance among all pairs of adult females separated by up to 10 km. At small distances (<0.8 km), CWD positive deer were more related than random individuals in the population, indicating a weak association between relatedness and CWD infection. This relationship was confounded by a low degree of spatial aggregation of related females compared to previous theories. Infection in adult females was strongly influenced by closely related females (full-sibling, mother-offspring) that were spatially proximate (<3.2 km). To a lesser extent, infection was also influenced by the number of infected nearby females (<3.2 km). In contrast, infection was not influenced by less genetically related females (i.e. half-sibling, grandmother-granddaughter, cousin) that were also expected to be in the same social group. Our results suggest a hierarchy of CWD transmission within social groups based on familial relationships. Our results indicate that direct (deer-to-deer) transmission of CWD likely occurs between closely related female deer. CWD transmission also appears to occur among spatially proximate females. However, we cannot determine whether occasional direct contact or contact with a contaminated environment is responsible for increased infection among proximate females. It is likely that direct and environmental (deer-environment-deer) transmission occurs in this epidemic. The influence of spatially proximate females and close female kin on CWD infection does not extend beyond a 2-3 km radius. In addition, the spatial relationship between infected females and among infected males and females suggests that CWD transmission operates on a local scale of 20-30 km2.