Sex-Specific Elk Resource Selection during the Anthrax Risk Period.

Anthrax, caused by the spore-forming bacterium Bacillus anthracis, is a zoonosis affecting animals and humans globally. In the United States, anthrax outbreaks occur in wildlife and livestock, with frequent outbreaks in native and exotic wildlife species in Texas, livestock outbreaks in the Dakotas, and sporadic mixed outbreaks in Montana. Understanding where pathogen and host habitat selection overlap is essential for anthrax management. Resource selection and habitat use of ungulates may be sex-specific and lead to differential anthrax exposure risks across the landscape for males and females. We evaluated female elk (Cervus canadensis) resource selection in the same study areas as male elk in a previous anthrax risk study to identify risk of anthrax transmission to females and compare transmission risk between females and males. We developed a generalized linear mixed-effect model to estimate resource selection for female elk in southwest Montana during the June to August anthrax transmission risk period. We then predicted habitat selection of female and male elk across the study area and compared selection with the distribution of anthrax risk to identify spatial distributions of potential anthrax exposure for the male and female elk. Female and male elk selected different resources during the anthrax risk period, which resulted in different anthrax exposure areas for females and males. The sex-specific resource selection and habitat use could infer different areas of risk for anthrax transmission, which can improve anthrax and wildlife management and have important public health and economic implications.

Anthrax Surveillance and the Limited Overlap Between Obligate Scavengers and Endemic Anthrax Zones in the United States.

Anthrax is a zoonosis caused by the spore-forming bacterium Bacillus anthracis, with potential for high fatality rate, especially in herbivores. Upon host death, spores can enter the soil surrounding the carcass and be ingested by other animals feeding in the same location. Accordingly, surveillance to quickly identify and decontaminate anthrax carcasses is crucial to outbreak prevention. In endemic anthrax areas such as Texas and Africa, vultures are used as a surveillance tool for identifying presence and location of dead animals. However, many anthrax outbreaks in the United States have occurred in areas outside the ranges of both black and turkey vultures. Here, we used a longitudinal camera trap survey at carcass sites in southwestern Montana to investigate the utility of facultative avian scavengers on disease and carcass surveillance in a reemerging anthrax risk zone. From August 2016 to September 2018, camera traps at 11 carcass sites were triggered 1996 times by avian scavengers. While the majority were facultative avian scavengers such as corvids and eagles, our results suggest that facultative scavengers cannot replace vultures as a surveillance tool in this ecosystem due to their absence during the anthrax risk period (June to August), reduced search efficiency, or low flight patterns. We found that the conditions in Montana likely parallel systems elsewhere in the continental United States. Using ecological niche models of B. anthracis distribution overlaid with relative abundance maps of turkey vultures, we found that much of North Dakota, South Dakota, Minnesota, Wyoming, Nebraska, and Iowa have areas of anthrax risk, but low or absent turkey vulture populations. Without vultures in these areas, surveillance capacity is reduced, and it becomes more difficult to identify anthrax cases, meaning fewer carcasses are decontaminated, and consequently, outbreaks could become more frequent or severe.

Factors influencing scavenger guilds and scavenging efficiency in Southwestern Montana.

Scavenging of carrion shapes ecological landscapes by influencing scavenger population demography, increasing inter- and intra-specific interactions, and generating ecosystem services such as nutrient cycling and disease moderation. Previous research found the cues promoting, or the constraints limiting, an individual's propensity or ability to scavenge vary widely, depending on anthropogenic and environmental factors. Here we investigated differences in scavenging patterns in a complex scavenger guild in Southwestern Montana. We used camera traps established at 13 carcass sites to monitor carcass detection, visitation, and consumption times, during 2016-2018 and generalized linear models to explore the influence of carcass characteristics, habitat features, and seasonality, on carcass selection and scavenging efficiency. We found that scavenger species diversity was higher at higher elevations and in grassland habitats. Scavenging efficiency was influenced inter alia by seasonality, distance to water, and elevation. We found that most carcass consumption was via facultative scavengers (bears, wolves, magpies, Corvus spp.) rather than turkey vultures, the only obligate scavengers in the study area. However, growing populations of turkey vultures may lead to increased competition with facultative scavengers over carrion, and could have cascading effects on food webs in this ecosystem.

Ungulate use of locally infectious zones in a re-emerging anthrax risk area.

Environmentally mediated indirect pathogen transmission is linked to host movement and foraging in areas where pathogens are maintained in the environment. In the case of anthrax, spores of the causative bacterium Bacillus anthracis are released into the environment following host death and create locally infectious zones (LIZs) around carcass sites; by grazing at LIZs, herbivores are potentially exposed to spores. Here, we used camera traps to assess how ungulate species use carcass sites in southwestern Montana and evaluated how these behaviours may promote indirect anthrax transmission, thus providing, to our knowledge, the first detailed documentation and study of the fine-scale mechanisms underlying foraging-based disease transmission in this ecosystem. We found that carcasses at LIZs significantly increased aboveground biomass of vegetation and concentrations of sodium and phosphorus, potentially making these sites more appealing to grazers. Host behavioural responses to LIZs varied depending on species, sex, season and carcass age; but, overall, our results demonstrated that carcasses or carcass sites serve as an attractant to herbivores in this system. Attraction to LIZs probably represents an increased risk of exposure to B. anthracis and, consequently, increased anthrax transmission rates. Accordingly, continued anthrax surveillance and control strategies are critical in this system.

Potential Bacillus anthracis Risk Zones for Male Plains Bison ( Bison bison bison) in Southwestern Montana, USA.

A re-emergence of anthrax, a zoonosis caused by the long-lived, spore-forming Bacillus anthracis, occurred with a multispecies outbreak in southwestern Montana, US in 2008. It substantially impacted a managed herd of about 3,500 free-ranging plains bison ( Bison bison bison) on a large, private ranch southwest of Bozeman, with about 8% mortality and a disproportionate 28% mortality of mature males; a similar high rate occurred in male Rocky Mountain elk ( Cervus canadensis nelson). Grazing herbivores are particularly at risk for anthrax from ingesting spore-contaminated soil and grasses in persistent environmental reservoirs. We predicted areas of mature male bison habitat preference on the landscape by using GPS collar data and a resource selection function model using environmental covariates. We overlaid preferred areas with ecologic niche, model-based predictions of B. anthracis environmental reservoirs to identify areas of high anthrax risk. Overlapping areas were distributed across the ranch and were not confined to pastures associated with the previous outbreak, suggesting that ongoing pasture exclusion alone will not prevent future outbreaks. The data suggested vaccination campaigns should continue for bison, and the results can be used to prioritize carcass surveillance in areas of greatest overlap.

Elk Resource Selection and Implications for Anthrax Management in Montana.

Anthrax, caused by the spore-forming bacterium Bacillus anthracis, is a zoonotic disease that affects humans and animals throughout the world. In North America, anthrax outbreaks occur in livestock and wildlife species. Vaccine administration in wildlife is untenable; the most effective form of management is surveillance and decontamination of carcasses. Successful management is critical because untreated carcasses can create infectious zones increasing risk for other susceptible hosts. We studied the bacterium in a re-emerging anthrax zone in southwest Montana. In 2008, a large anthraxepizootic primarily affected a domestic bison (Bison bison) herd and the male segment of a free-ranging elk (Cervus elaphus) herd in southwestern Montana. Following the outbreak, we initiated a telemetry study on elk to evaluate resource selection during the anthrax season to assist with anthrax management. We used a mixed effects generalized linear model (GLM) to estimate resource selection by male elk, and we mapped habitat preferences across the landscape. We overlaid preferred habitats on ecological niche model-based estimates of B. anthracis presence. We observed significant overlap between areas with a high predicted probability of male elk selection and B. anthracis potential. These potentially risky areas of elk and B. anthracis overlap were broadly spread over public and private lands. Future outbreaks in the region are probable, and this analysis identified the spatial extent of the risk area in the region, which can be used to prioritize anthrax surveillance.

Dances with anthrax: wolves (Canis lupus) kill anthrax bacteremic plains bison (Bison bison bison) in southwestern Montana.

Bacillus anthracis, the cause of anthrax, was recovered from two plains bison (Bison bison bison) cows killed by wolves (Canis lupus) in Montana, USA, without associated wolf mortality in July 2010. This bison herd experienced an epizootic in summer 2008, killing ∼ 8% of the herd, the first documented in the region in several decades. No wolf deaths were associated with the 2008 event. Surveillance has continued since 2008, with research, ranch, and wildlife personnel diligent during summer. As part of this, we tested wolf-killed bison and elk (Cervus elaphus) for anthrax during the 2010 summer using lateral flow immunochromatographic assays (LFIA). Two bison cows were positive for protective antigen, confirming active bacteremia. The LFIA results were confirmed with traditional bacteriology recovering viable B. anthracis. No wolf fatalities were associated with the bison deaths, despite consuming the meat. Low-level anthrax occurrence in large, rough terrain landscapes remains difficult to detect, particularly if mortality in the herbivore host is not a consequence of infection. In these instances, surveillance of predators with large home ranges may provide a more sensitive indicator of anthrax emergence or reemergence in such systems. Though speculative, it is also possible that anthrax infection in the bison increased predation risk. These results also suggest B. anthracis remains a threat to wildlife and associated livestock in southwestern Montana.

Sarcoptic mange found in wolves in the Rocky Mountains in western United States.

We documented sarcoptic mange caused by mites (Sarcoptes scabiei) in 22 gray wolves (Canis lupus) in the northern Rocky Mountain states of Montana (n=16) and Wyoming (n=6), from 2002 through 2008. To our knowledge, this is the first report of sarcoptic mange in wolves in Montana or Wyoming in recent times. In addition to confirming sarcoptic mange, we recorded field observations of 40 wolves in Montana and 30 wolves in Wyoming displaying clinical signs of mange (i.e., alopecia, hyperkeratosis, and seborrhea). Therefore, we suspect sarcoptic mange may be more prevalent than we were able to confirm.