Epidemiology of chronic wasting disease in captive white-tailed and mule deer

The natural occurrence of chronic wasting disease (CWD) in a 1993 cohort of captive white-tailed deer (Odocoileus virginianus) afforded the opportunity to describe epidemic dynamics in this species and to compare dynamics with those seen in contemporary cohorts of captive mule deer (O. hemionus) also infected with CWD. The overall incidence of clinical CWD in white-tailed deer was 82% (nine of 11) among individuals that survived >15 mo. Affected white-tailed deer died or were killed because of terminal CWD at age 49-76 mo (x = 59.6 mo, SE = 3.9 mo). Epidemic dynamics of CWD in captive white-tailed deer were similar to dynamics in mule deer cohorts. Incidence of clinical CWD was 57% (4/7) among hand-raised (HR) and 67% (4/6) among dam-raised (DR) mule deer; affected HR mule deer succumbed at 64-86 mo of age (x = 72 mo; SE = 5 mo), and affected DR mule deer died at age 31-58 mo (x = 41.3 mo; SE = 6.1 mo). Sustained horizontal transmission of CWD most plausibly explained epidemic dynamics, but the original source of exposures could not be determined. Apparent differences in mean age at CWD-caused death among these cohorts may be attributable to differences in the timing or intensity of exposure to CWD, and these factors appear to be more likely to influence epidemic dynamics than species differences. It follows that CWD epidemic dynamics in sympatric, free-ranging white-tailed and mule deer sharing habitats in western North American ranges also may be similar.     

Failure of fallow deer (Dama dama) to develop chronic wasting disease when exposed to a contaminated environment and infected mule deer (Odocoileus hemionus)

We monitored a herd of fallow deer (Dama dama) for evidence of prion infection for 7 yr by periodic postmortem examination of animals from the herd. The fallow deer were exposed to the chronic wasting disease (CWD) agent from mule deer by living in a paddock considered contaminated with infectivity from its history of housing CWD infected deer and, after the first year of the study, by comingling with infected mule deer (Odocoileus hemionus). At least 8 of 12 mule deer serving as sentinels for prion transmission and 25 additional mule deer serving as sources of infectivity developed clinical CWD or were otherwise confirmed to be infected with CWD via lymphoid tissue immunohistochemistry (IHC). In contrast, none of the 41 exposed fallow deer showed clinical signs suggestive of CWD, IHC staining of disease-associated prion in lymphoid or brain tissues, or evidence of spongiform degeneration in sections of brain stem at the level of the obex when sampled 18 mo to 7 yr after entering the mule deer paddock. The absence of clinical disease and negative IHC results in fallow deer housed in the same contaminated paddock for up to 7 yr and almost continuously exposed to CWD-infected mule deer for up to 6 yr suggests a species barrier or other form of resistance preventing fallow deer infection by the CWD agent or delaying progression of the disease in this species.     

Interaction among deer in a chronic wasting disease endemic zone

Although it is known that chronic wasting disease (CWD) can be transmitted by both direct animal-to-animal contact and contact with contaminated environments, the relative role of each mechanism in the spread of CWD in free-ranging populations has yet to be defined. We investigated patterns of interaction between mule deer (Odocoileus hemionus) in order to understand how factors such as season and landscape may influence patterns of disease spread in these populations. Using location data from male and female Global Positioning System (GPS)-collared mule deer in 5 study areas located in and around a CWD-endemic zone in southern Saskatchewan, Canada, we quantified close proximity events, or events involving both spatial and temporal overlap of individuals. We defined close proximity events as occurrences in which 2 deer were located <25 m apart at the same point in time. We looked at seasonal variation in the probability of close proximity events, as well as landscape factors associated with these events when compared to areas of shared space use, or spatial overlap alone. Overall probability of an individual GPS-collared deer being located in close proximity to another GPS-collared deer was 0.092 (n = 107). The early gestation (16 Dec–31 Mar) and late gestation (1 Apr–15 May) seasons had the highest probability of close proximity events occurring, and same-sex pairs were more likely to be found in close proximity than between-sex pairs during all seasons aside from the rut (1 Nov–15 Dec). High probability of close proximity events during the gestation seasons agrees with the tendency of mule deer to aggregate into large groups during late winter and suggests that this may be an important time period for CWD transmission to occur. Close proximity events occurred more in cropland and wetland than expected based on availability, whereas close proximity events occurred less than expected in grassland. The opposite was true for spatial overlap between individuals, which occurred more than expected in areas of low elevation and rugged terrain and in grassland or shrub–wood habitats. These results suggest that cropland may be a higher risk habitat for direct and indirect CWD transmission between individuals and that, although coulees and other areas of rugged topography are less likely to be associated with close proximity events, those areas may be more likely to contain environmental contamination in CWD-affected areas due to common use by multiple deer. © 2011 The Wildlife Society.     

Relative vulnerability of chronic wasting disease infected mule deer to vehicle collisions

We estimated chronic wasting disease (CWD) prevalence among vehicle-killed mule deer (Odocoileus hemionus) in select data analysis units (DAUs) in northern Colorado, USA, and compared these with estimated CWD prevalence among mule deer of the same sex sampled in the vicinity of collision sites to assess relative vulnerability of CWD-infected individuals to vehicle collisions. Twenty-five of 171 vehicle-killed mule deer tested positive for CWD (overall prevalence=0.146, 95% confidence interval [CI]=0.097-0.208); 173 of 2,317 deer sampled in the vicinity of these vehicle-killed deer tested positive (overall prevalence=0.075, 95% CI=0.064-0.085). In nine of ten DAU x sex comparisons, relative risk of CWD infection tended to be higher among vehicle-killed deer (range of estimated relative risks=1.6-15.9). Spongiform encephalopathy was detected in 12 of 20 (60%; 95% CI=39-81%) CWD-positive deer killed by vehicles and in 79 of 180 (44%; 95% CI=37-52%) CWD-positive deer detected via random sampling (relative risk=1.37; 95% CI=0.92-2.03), suggesting that infected deer killed by vehicles tended to be in later stages of disease than those killed by hunters. Our data offer evidence that CWD-infected mule deer may be relatively vulnerable to vehicle collisions. It follows that sampling of vehicle-killed mule deer may be exploited to increase efficiency of surveillance programs designed to detect new foci of CWD infection; moreover, evidence of increased susceptibility to vehicle collisions may aid in understanding vulnerability of CWD-infected individuals to other forms of death, particularly predation.     

Infectious Disease and Grouping Patterns in Mule Deer

Infectious disease dynamics are determined, to a great extent, by the social structure of the host. We evaluated sociality, or the tendency to form groups, in Rocky Mountain mule deer (Odocoileus hemionus hemionus) from a chronic wasting disease (CWD) endemic area in Saskatchewan, Canada, to better understand factors that may affect disease transmission. Using group size data collected on 365 radio-collared mule deer (2008–2013), we built a generalized linear mixed model (GLMM) to evaluate whether factors such as CWD status, season, habitat and time of day, predicted group occurrence. Then, we built another GLMM to determine factors associated with group size. Finally, we used 3 measures of group size (typical, mean and median group sizes) to quantify levels of sociality. We found that mule deer showing clinical signs of CWD were less likely to be reported in groups than clinically healthy deer after accounting for time of day, habitat, and month of observation. Mule deer groups were much more likely to occur in February and March than in July. Mixed-sex groups in early gestation were larger than any other group type in any season. Groups were largest and most likely to occur at dawn and dusk, and in open habitats, such as cropland. We discuss the implication of these results with respect to sociobiology and CWD transmission dynamics.     

Genetic assessment of environmental features that influence deer dispersal: implications for prion-infected populations

The landscape can influence host dispersal and density, which in turn, affect infectious disease transmission, spread, and persistence. Understanding how the landscape influences wildlife dispersal and pathogen epidemiology can enhance the efficacy of disease management in natural populations. We applied landscape genetics to examine relationships among landscape variables, dispersal of white-tailed deer hosts and transmission/spread of chronic wasting disease (CWD), a fatal prion encephalopathy. Our focus was on quantifying movements and population structure of host deer in infected areas as a means of predicting the spread of this pathology and promoting its adaptive management. We analyzed microsatellite genotypes of CWD-infected and uninfected deer from two disease foci (Southern Wisconsin, Northern Illinois). We quantified gene flow and population structure using F _ST, assignment tests, and spatial autocorrelation analyses. Gene flow estimates were then contrasted against a suite of landscape variables that potentially mediate deer dispersal. Forest fragmentation and grassland connectivity promoted deer movements while rivers, agricultural fields and large urbanized areas impeded movement. Landscape variables, deer dispersal, and disease transmission covaried significantly and positively in our analyses. Habitats with elevated host gene flow supported the concept of dispersal-mediated CWD transmission by reflecting a concomitant, rapid CWD expansion. Large, interrelated social groups isolated by movement barriers overlapped disease foci, suggesting that philopatry exacerbated CWD transmission. Our results promote adaptive management of CWD by predicting patterns of its spread and identifying habitats at risk for invasion. Further, our landscape genetics approach underscores the significance of topography and host behavior in wildlife disease transmission.     

Prevalence of chronic wasting disease and bovine tuberculosis in free-ranging deer and elk in South Dakota

Heads of hunter-harvested deer and elk were collected throughout South Dakota (USA) and within established chronic wasting disease (CWD) surveillance areas from 1997-2002 to determine infection with CWD and bovine tuberculosis (TB). We used immunohistochemistry to detect CWD-infected individuals among 1,672 deer and elk sampled via geographically targeted surveillance. A total of 537 elk (Cervus elaphus nelsoni), 813 white-tailed deer (Odocoileus virginianus), and 322 mule deer (O. hemionus) was sampled for CWD. Estimated overall prevalence and associated confidence intervals (95%) in white-tailed deer was 0.001% (0-0.007%). Similarly, estimated overall prevalence in elk and mule deer was 0.0% (0-0.004%) and 0.0% (0-0.011%), respectively. A total of 401 elk, 1,638 white-tailed deer, and 207 mule deer was sampled for TB. Estimated overall prevalence of infection with TB in elk harvested in South Dakota was 0.0% (0-0.009%). Similarly, estimated overall prevalence of TB in white-tailed deer and mule deer harvested throughout South Dakota was 0.0% (0-0.002%) and 0.0% (0-0.018%), respectively.     

Bayesian Modeling of Prion Disease Dynamics in Mule Deer Using Population Monitoring and Capture-Recapture Data

Epidemics of chronic wasting disease (CWD) of North American Cervidae have potential to harm ecosystems and economies. We studied a migratory population of mule deer (Odocoileus hemionus) affected by CWD for at least three decades using a Bayesian framework to integrate matrix population and disease models with long-term monitoring data and detailed process-level studies. We hypothesized CWD prevalence would be stable or increase between two observation periods during the late 1990s and after 2010, with higher CWD prevalence making deer population decline more likely. The weight of evidence suggested a reduction in the CWD outbreak over time, perhaps in response to intervening harvest-mediated population reductions. Disease effects on deer population growth under current conditions were subtle with a 72% chance that CWD depressed population growth. With CWD, we forecasted a growth rate near one and largely stable deer population. Disease effects appear to be moderated by timing of infection, prolonged disease course, and locally variable infection. Long-term outcomes will depend heavily on whether current conditions hold and high prevalence remains a localized phenomenon.     

Inhibition of protease-resistant prion protein formation in a transformed deer cell line infected with chronic wasting disease

Chronic wasting disease (CWD) is an emerging transmissible spongiform encephalopathy (prion disease) of North American cervids, i.e., mule deer, white-tailed deer, and elk (wapiti). To facilitate in vitro studies of CWD, we have developed a transformed deer cell line that is persistently infected with CWD. Primary cultures derived from uninfected mule deer brain tissue were transformed by transfection with a plasmid containing the simian virus 40 genome. A transformed cell line (MDB) was exposed to microsomes prepared from the brainstem of a CWD-affected mule deer. CWD-associated, protease-resistant prion protein (PrP(CWD)) was used as an indicator of CWD infection. Although no PrP(CWD) was detected in any of these cultures after two passes, dilution cloning of cells yielded one PrP(CWD)-positive clone out of 51. This clone, designated MDB(CWD), has maintained stable PrP(CWD) production through 32 serial passes thus far. A second round of dilution cloning yielded 20 PrP(CWD)-positive subclones out of 30, one of which was designated MDB(CWD2). The MDB(CWD2) cell line was positive for fibronectin and negative for microtubule-associated protein 2 (a neuronal marker) and glial fibrillary acidic protein (an activated astrocyte marker), consistent with derivation from brain fibroblasts (e.g., meningeal fibroblasts). Two inhibitors of rodent scrapie protease-resistant PrP accumulation, pentosan polysulfate and a porphyrin compound, indium (III) meso-tetra(4-sulfonatophenyl)porphine chloride, potently blocked PrP(CWD) accumulation in MDB(CWD) cells. This demonstrates the utility of these cells in a rapid in vitro screening assay for PrP(CWD) inhibitors and suggests that these compounds have potential to be active against CWD in vivo.     

Estimating chronic wasting disease effects on mule deer recruitment and population growth

Chronic wasting disease (CWD), a prion disease of mule deer (Odocoileus hemionus), accelerates mortality and in so doing has the potential to influence population dynamics. Although effects on mule deer survival are clear, how CWD affects recruitment is less certain. We studied how prion infection influenced the number of offspring raised to weaning per adult (≥2 yr old) female mule deer and subsequently the estimated growth rate (λ) of an infected deer herd. Infected and presumably uninfected radio-collared female deer were observed with their fawns in late summer (August-September) during three consecutive years (2006-2008) in the Table Mesa area of Boulder, Colorado, USA. We counted the number of fawns accompanying each female, then used a fully Bayesian model to estimate recruitment by infected and uninfected females and the effect of the disease on λ. On average, infected females weaned 0.95 fawns (95% credible interval=0.56-1.43) whereas uninfected females weaned 1.34 fawns (95% credible interval=1.09-1.61); the probability that uninfected females weaned more fawns than infected females was 0.93). We used estimates of prevalence to weight recruitment and survival parameters in the transition matrix of a three-age, single-sex matrix model and then used the matrix to calculate effects of CWD on λ. When effects of CWD on both survival and recruitment were included, the modeled λ was 0.97 (95% credible interval = 0.82-1.09). Effects of disease on λ were mediated almost entirely by elevated mortality of infected animals. We conclude that although CWD may affect mule deer recruitment, these effects seem to be sufficiently small that they can be omitted in estimating the influences of CWD on population growth rate.     

Salivary prions in sheep and deer

Scrapie of sheep and chronic wasting disease (CWD) of cervids are transmissible prion diseases. Milk and placenta have been identified as sources of scrapie prions but do not explain horizontal transmission. In contrast, CWD prions have been reported in saliva, urine and feces, which are thought to be responsible for horizontal transmission. While the titers of CWD prions have been measured in feces, levels in saliva or urine are unknown. Because sheep produce ∼17 L/day of saliva and scrapie prions are present in tongue and salivary glands of infected sheep, we asked if scrapie prions are shed in saliva. We inoculated transgenic (Tg) mice expressing ovine prion protein, Tg(OvPrP) mice, with saliva from seven Cheviot sheep with scrapie. Six of seven samples transmitted prions to Tg(OvPrP) mice with titers of −0.5 to 1.7 log ID₅₀ U/ml. Similarly, inoculation of saliva samples from two mule deer with CWD transmitted prions to Tg(ElkPrP) mice with titers of −1.1 to −0.4 log ID₅₀ U/ml. Assuming similar shedding kinetics for salivary prions as those for fecal prions of deer, we estimated the secreted salivary prion dose over a 10-mo period to be as high as 8.4 log ID₅₀ units for sheep and 7.0 log ID₅₀ units for deer. These estimates are similar to 7.9 log ID₅₀ units of fecal CWD prions for deer. Because saliva is mostly swallowed, salivary prions may reinfect tissues of the gastrointestinal tract and contribute to fecal prion shedding. Salivary prions shed into the environment provide an additional mechanism for horizontal prion transmission.Key words: scrapie, chronic wasting disease, saliva, horizontal transmission, titers     

Transmission of elk and deer prions to transgenic mice

Chronic wasting disease (CWD) is a fatal prion disease in deer and elk. Unique among the prion diseases, it is transmitted among captive and free-ranging animals. To facilitate studies of the biology of CWD prions, we generated five lines of transgenic (Tg) mice expressing prion protein (PrP) from Rocky Mountain elk (Cervus elaphus nelsoni), denoted Tg(ElkPrP), and two lines of Tg mice expressing PrP common to white-tailed deer (Odocoileus virginianus) and mule deer (Odocoileus hemionus), denoted Tg(DePrP). None of the Tg(ElkPrP) or Tg(DePrP) mice exhibited spontaneous neurologic dysfunction at more than 600 days of age. Brain samples from CWD-positive elk, white-tailed deer, and mule deer produced disease in Tg(ElkPrP) mice between 180 and 200 days after inoculation and in Tg(DePrP) mice between 300 and 400 days. One of eight cervid brain inocula transmitted disease to Tg(MoPrP)4053 mice overexpressing wild-type mouse PrP-A in approximately 540 days. Neuropathologic analysis revealed abundant PrP amyloid plaques in the brains of ill mice. Brain homogenates from symptomatic Tg(ElkPrP) mice produced disease in 120 to 190 days in Tg(ElkPrP) mice. In contrast to the Tg(ElkPrP) and Tg(DePrP) mice, Tg mice overexpressing human, bovine, or ovine PrP did not develop prion disease after inoculation with CWD prions from among nine different isolates after >500 days. These findings suggest that CWD prions from elk, mule deer, and white-tailed deer can be readily transmitted among these three cervid species.     

Epizootiology of chronic wasting disease in free-ranging cervids in Colorado and Wyoming

Surveillance and epidemic modeling were used to study chronic wasting disease (CWD), a transmissible spongiform encephalopathy that occurs naturally among sympatric, free-ranging deer (Odocoileus spp.) and Rocky Mountain elk (Cervus elaphus nelsoni) populations in contiguous portions of northeastern Colorado and southeastern Wyoming (USA). We used clinical case submissions to identify endemic areas, then used immunohistochemistry to detect CWD-infected individuals among 5,513 deer and elk sampled via geographically-focused random surveys. Estimated overall prevalence (prevalence, 95% confidence interval) in mule deer (4.9%, 4.1 to 5.7%) was higher than in white-tailed deer (2.1%, 0.5 to 3.4%) or elk (0.5%, 0.001 to 1%) in endemic areas; CWD was not detected in outlying portions of either state. Within species, CWD prevalence varied widely among biologically- or geographically-segregated subpopulations within the 38,137 km2 endemic area but appeared stable over a 3-yr period. The number of clinical CWD cases submitted from an area was a poor predictor of local CWD prevalence, and prevalence was typically > or =1% before clinical cases were first detected in most areas. Under plausible transmission assumptions that mimicked field data, prevalence in epidemic models reached about 1% in 15 to 20 yr and about 15% in 37 to 50 yr. Models forecast population declines once prevalence exceeded about 5%. Both field and model data supported the importance of lateral transmission in CWD dynamics. Based on prevalence, spatial distribution, and modeling, we suggest CWD has been occurring in northeastern Colorado and southeastern Wyoming for >30 yr, and may be best represented as an epizootic with a protracted time-scale.     

A qualitative model for aggregation and diffusion of \beta -amyloid in Alzheimer’s disease

In this paper we present a mathematical model for the aggregation and diffusion of A $\beta $ amyloid in the brain affected by Alzheimer’s disease, at the early stage of the disease. The model is based on a classical discrete Smoluchowski aggregation equation modified to take diffusion into account. We also describe a numerical scheme and discuss the results of the simulations in the light of the recent biomedical literature.     

Influence of interspecific competition on mule deer birthing and rearing site selection

Ungulates often alter behavior and space use in response to interspecific competition. Despite observable changes in behavior caused by competitive interactions, research describing the effects of competition on survival or growth is lacking. We used spatial modeling to determine if habitat use by female mule deer (Odocoileus hemionus) was affected by other ungulate species prior to, during, and after parturition. We conducted our study in the Book Cliffs region of eastern Utah, USA, during 2019 and 2020. We used resource selection function (RSF) analysis to model space use of 4 ungulate species that potentially competed with mule deer: bison (Bos bison), cattle, elk (Cervus canadensis), and feral horses. We incorporated RSF models for competing species into a random forest analysis to determine if space use by mule deer was influenced by these other ungulate species. We used survival and growth data from neonate mule deer to directly assess potential negative effects of other ungulates. Habitat use by elk was an important variable in predicting use locations of mule deer during birthing and rearing. The relationship was positive, suggesting interference competition was not occurring. Survival of neonate mule deer increased as the probability of use by elk increased (hazard ratio = 0.185 ± 0.497 [SE]). Further, probability of use by elk in rearing habitat had no influence on growth of neonate mule deer from birth to 6 months of age, suggesting that exploitative competition was not occurring.     

Population genetic structure of white-tailed deer: Understanding risk of chronic wasting disease spread

Understanding factors that influence the spread of wildlife diseases can assist in designing effective surveillance programs and appropriate management strategies. Chronic wasting disease (CWD), a fatal prion disease of cervids, was detected in south-central Wisconsin in 2002 and over time has been identified increasingly farther west in the state leading to concerns about CWD spreading to Iowa. Our objective was to characterize genetic connectivity between white-tailed deer (Odocoileus virginianus) populations in eastern Iowa and western Wisconsin to assess the risk of CWD-infected deer dispersing to Iowa. We hypothesized that the Mississippi River, which separates the states, may restrict the movement of deer and thus disease. We genotyped hunter-harvested female deer collected from both states at 12 nuclear microsatellite loci (n = 249) and sequenced a portion of the mitochondrial DNA (mtDNA) control region (n = 173). Microsatellite data indicated there was low genetic differentiation (Φ_PT = 0.005) between states and weak spatial genetic structure across the study area as a whole. Verifying expectations that dispersal in deer is male-biased, maternally inherited mtDNA data showed stronger spatial structuring across the study area and greater genetic differentiation between the states (Φ_PT = 0.052) such that clustering analysis grouped the majority of deer from Iowa and Wisconsin into separate clusters. The low level of genetic differentiation between deer in northeast Iowa and southwest Wisconsin, primarily the result of dispersing males who have greater CWD prevalence than females, indicates that the Mississippi River is unlikely to prohibit the westward spread of CWD, and underscores the importance of continued CWD surveillance in Iowa. © 2011 The Wildlife Society.     

Interspecies transmission of chronic wasting disease prions to squirrel monkeys (Saimiri sciureus)

Chronic wasting disease (CWD) is an emerging prion disease of deer and elk. The risk of CWD transmission to humans following exposure to CWD-infected tissues is unknown. To assess the susceptibility of nonhuman primates to CWD, two squirrel monkeys were inoculated with brain tissue from a CWD-infected mule deer. The CWD-inoculated squirrel monkeys developed a progressive neurodegenerative disease and were euthanized at 31 and 34 months postinfection. Brain tissue from the CWD-infected squirrel monkeys contained the abnormal isoform of the prion protein, PrP-res, and displayed spongiform degeneration. This is the first reported transmission of CWD to primates.     

Transmission of prions from mule deer and elk with chronic wasting disease to transgenic mice expressing cervid PrP

We generated mice expressing cervid prion protein to produce a transgenic system simulating chronic wasting disease (CWD) in deer and elk. While normal mice were resistant to CWD, these transgenic mice uniformly developed signs of neurological dysfunction approximately 230 days following intracerebral inoculation with four CWD isolates. Inoculated transgenic mice homozygous for the transgene array developed disease after approximately 160 days. The brains of sick transgenic mice exhibited widespread spongiform degeneration and contained abnormal prion protein and abundant amyloid plaques, many of which were florid plaques. Transmission studies indicated that the same prion strain caused CWD in the analyzed mule deer and elk. These mice provide a new and reliable tool for detecting CWD prions.     

Does small-perimeter fencing inhibit mule deer or pronghorn use of water developments?

Wildlife water development can be an important habitat management strategy in western North America for many species, including both pronghorn (Antilocapra americana) and mule deer (Odocoileus hemionus). In many areas, water developments are fenced (often with small-perimeter fencing) to exclude domestic livestock and feral horses. Small-perimeter exclosures could limit wild ungulate use of fenced water sources, as exclosures present a barrier pronghorn and mule deer must negotiate to gain access to fenced drinking water. To evaluate the hypothesis that exclosures limit wild ungulate access to water sources, we compared use (photo counts) of fenced versus unfenced water sources for both pronghorn and mule deer between June and October 2002–2008 in western Utah. We used model selection to identify an adequate distribution and best approximating model. We selected a zero-inflated negative binomial distribution for both pronghorn and mule deer photo counts. Both pronghorn and mule deer photo counts were positively associated with sampling time and average daily maximum temperature in top models. A fence effect was present in top models for both pronghorn and mule deer, but mule deer response to small-perimeter fencing was much more pronounced than pronghorn response. For mule deer, we estimated that presence of a fence around water developments reduced photo counts by a factor of 0.25. We suggest eliminating fencing of water developments whenever possible or fencing a big enough area around water sources to avoid inhibiting mule deer. More generally, our results provide additional evidence that water development design and placement influence wildlife use. Failure to account for species-specific preferences will limit effectiveness of management actions and could compromise research results. © 2011 The Wildlife Society.     

Epidemiology of chronic wasting disease in free-ranging mule deer: spatial, temporal, and demographic influences on observed prevalence patterns

We analyzed chronic wasting disease (CWD) prevalence data from mule deer populations in northcentral Colorado, USA, to discern the likely influences of temporal, spatial, and demographic factors on patterns observed in naturally infected populations. In addition to reaffirming spatial heterogeneity among wintering mule deer subpopulations, we report marked differences in CWD prevalence by sex and age groups as well as clear local trends of increasing prevalence over a 7-yr period. Prevalence of CWD differed by age (yearling vs. adult), sex, and geographic area at two different spatial scales (game management unit or population unit winter range) and increased over time at both geographic scales. Disease status (positive or negative) was not independent of age for males (n=285, df=6, chi2=18.4, P=0.005) or females (n=387, df=8, chi2=17.2, P=0.028). Among males, prevalence increased and then declined across age classes, peaking in 5- to 6-yr-old individuals; among females, prevalence showed no definite age-related pattern. Demographic, spatial, and temporal factors all appear to contribute to the marked heterogeneity in CWD prevalence in endemic portions of northcentral Colorado, USA. These factors likely combine in various ways to influence epidemic dynamics on both local and broad geographic scales.