Saturday, March 05, 2016
Social affiliation and contact patterns among white-tailed deer in disparate landscapes: implications for disease transmission
Eric M. Schauber, Clayton K. Nielsen, Lene J. Kjær, Charles W. Anderson, Daniel J. Storm
DOI: http://dx.doi.org/10.1093/jmammal/gyu027 16-28 First published online: 27 March 2015
In social species, individuals contact members of the same group much more often than those of other groups, particularly for contacts that could directly transmit disease agents. This disparity in contact rates violates the assumptions of simple disease models, hinders disease spread between groups, and could decouple disease transmission from population density. Social behavior of white-tailed deer has important implications for the long-term dynamics and impact of diseases such as bovine tuberculosis and chronic wasting disease (CWD), so expanding our understanding of their social system is important. White-tailed deer form matrilineal groups, which inhabit stable home ranges that overlap somewhat with others—a pattern intermediate between mass-action and strict territoriality. To quantify how group membership affects their contact rates and document the spectrum of social affiliation, we analyzed location data from global positioning system (GPS) collars on female and juvenile white-tailed deer in 2 study areas: near Carbondale in forest-dominated southern Illinois (2002–2006) and near Lake Shelbyville in agriculture-dominated central Illinois (2006–2009). For each deer dyad (i.e., 2 individual deer with sufficient overlapping GPS data), we measured space-use overlap, correlation of movements, direct contact rate (simultaneous GPS locations < 10 m apart), and indirect contact rate (GPS locations < 10 m apart when offset by 1 or 3 days). Direct contact rates were substantially higher for within-group dyads than between-group dyads, but group membership had little apparent effect on indirect contact rates. The group membership effect on direct contact rates was strongest in winter and weakest in summer, with no apparent difference between study areas. Social affiliations were not dichotomous, with some deer dyads showing loose but positive affiliation. Even for obvious within-group dyads, their strength of affiliation fluctuated between years, seasons, and even days. Our findings highlight the poor fit between deer behavior and simple models of disease transmission and, combined with previous infection data, suggest that direct contact is the primary driver of CWD transmission among free-living female and juvenile white-tailed deer.
Key words:contact disease global positioning system group Illinois landscape Odocoileus virginianus transmission white-tailed deer
Relating social contact patterns to infection patterns can help shed light on fundamental questions of wildlife disease dynamics. For example, CWD can be transmitted by both direct and indirect routes and indirect transmission of CWD appears to be common in captive cervids; however, the relative importance of direct and indirect contact for free-living cervid populations is unknown (Miller and Williams 2003; Miller et al. 1998, 2000, 2004, 2006). Grear et al. (2010) examined patterns of CWD infection in female white-tailed deer harvested in south-central Wisconsin and found that the presence of a closely related female deer infected with CWD in close proximity increased the odds of being infected by > 100-fold relative to the presence of an unrelated infected female (ln odds ratio [β] = 4.93 for related and 0.09 for unrelated, exp[4.93−0.09] = 126). Their findings indicate that CWD transmission occurs much more readily between members of the same matrilineal social group than between groups or from males to females. Combining that result with our data indicating that the distinction between within- and between-group contact rates is much stronger for direct than indirect contacts, we find that the evidence is most consistent with the hypothesis that direct transmission is the dominant mode of CWD spread among free-living female white-tailed deer, at least at the present stage of the epizootic. Because prions that cause CWD can persist for long periods in the environment (Miller et al. 2004; Pedersen et al. 2006), the relative importance of indirect transmission could increase as time progresses and infection prevalence increases (Almberg et al. 2011). However, recent research suggests that prion infectivity is substantially higher via inhalation of aerosol than via ingestion (Denkers et al. 2013), again pointing to a key role for close physical proximity in CWD transmission.
Tuesday, February 02, 2016
Illinois six out of 19 deer samples tested positive for CWD in the Oswego zone of Kendall County
Friday, February 05, 2016
Report of the Committee on Wildlife Diseases FY2015 CWD TSE PRION Detections in Farmed Cervids and Wild
Saturday, February 6, 2016
Secretary's Advisory Committee on Animal Health; Meeting [Docket No. APHIS-2016-0007] Singeltary Submission
kind regards, terry