Interaction among deer in a chronic wasting disease endemic zone

Abstract

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 CWDendemic 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 ¼ 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. ß 2011 The Wildlife Society.

Mule deer spatial association patterns and potential implications for transmission of an epizootic disease

“…Mule deer have a marked right-skewed distribution of group sizes [25] with obvious seasonality driven by environmental conditions and reproductive behaviour [25, 28–31]. The largest mixed-sex groups are observed in winter, while the smallest are seen during the fawning period [25, 29].…”

“…The largest mixed-sex groups are observed in winter, while the smallest are seen during the fawning period [25, 29]. In our study area, open flat habitat is associated with larger groups and a greater frequency of close proximity events (deer within 25 m of each other), while rugged terrain is used by many individuals in small groups [25, 28]. …”

Comparing radio-tracking and visual detection methods to quantify group size measures

“…A study on chronic wasting disease (CWD) transmission dynamics was conducted at Antelope Creek (50.66°N, 108.27°W), a 248 km 2 CWD endemic area in south Saskatchewan, Canada (Silbernagel 2011;Mejía Salazar et al 2016). This study site is within the mixed grassland ecoregion and consists of crop (46.6%), grassland (35.6%), shrub (7.6%), woodland (2%) and open water (0.3%).…”

Potential role of soil properties in the spread of CWD in western Canada

“…8,9 Therefore, soil properties are an important factor for PrP TSE preservation and transmission in the environment. [10][11][12][13] Analysis of soil-prion interactions and the impact on infectivity is a complicated task because soils are multicomponent systems consisting of mineral particles (clay, silt, sand); soil organic matter (humic, fulvic acids and humin); humus or/and Fe-Mn films and cutans interacting with mineral particles. The enormous complexity of soils indicates a need to examine a variety of soils and their separated compounds (mineral and organic) to identify the ability of prions to bind the soil, what the effect of binding is on infectivity and what components of soil bind prions.…”

“…A recent study in southern Saskatchewan has suggested the importance of landscape position for CWD transmission: croplands have a higher risk compared with coulees and creek valleys. 13 This correlation may be related to soil properties because soil texture, organic matter content, pH etc. usually vary with topography.…”