Sex‐Specific Elk Resource Selection during the Anthrax Risk Period

Abstract

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.

A framework for integrating inferred movement behavior into disease risk models

“…The spatial distribution of such pathogens can be readily modeled using remotely-sensed proxies of various environmental factors [ 22 ], making studies of their overlap with host animals especially fruitful. Two prior studies of such overlap were carried out based on seasonal habitat preference using a resource selection function (RSF) framework [ 23 , 24 ]; while informative, these studies did not include avoidance behavior at the much finer step selection level [ 25 , 26 ], as we present here.…”

Some Peculiarities of Anthrax Epidemiology in Herbivorous and Carnivorous Animals

“…While adult animals are susceptible to infection, young animals are relatively resistant, and among adults, fertile males are the most affected. This phenomenon has been described for livestock [ 23 , 24 ], wild bison [ 25 , 26 ], moose [ 25 , 27 ], and many African herbivores, including not only ungulates, but also Proboscidea (African elephant) [ 13 ]. There is no exhaustive explanation of these phenomena, or at least one confirmed by experiments or field observations; nevertheless, it is possible to put forward some hypotheses.…”

“…In addition, they feed on coarser vegetation. This increases both the likelihood of receiving microtraumas of the upper parts of the digestive system, which become the entrance gate of infection, and the duration of digestion, primarily in the rumen [ 25 , 27 , 36 ]. Considering the abovementioned model of spore germination as the initial stage of gastrointestinal anthrax development, such food segregation may increase the likelihood of males becoming sick when feeding on vegetation contaminated with B. anthracis spores.…”

“…If this death occurred due to anthrax, the male who reoccupied this territory is at an increased risk of infection, since it begins to graze in an epidemically dangerous area. In addition, the relatively large body size and higher aggressiveness of males means that large herbivore males avoid the risk of meeting predators to a lesser extent than females and calves [ 25 , 27 ]. In particular, they will be less likely to be scared away by predators gnawing the carcass of an animal killed by anthrax and contaminating the surrounding soil and vegetation, which, again, increases the risk of infection.…”

Routes of Spread of Anthrax in Natural Ecosystems

“…При этом самцы зачастую питаются более грубой растительностью, что увеличивает вероятность получения микротравм верхних отделов пищеварительной системы, которые, по мнению некоторых авторов [9], могут сыграть роль входных ворот инфекции. Но, на наш взгляд, важнее то, что большая доля в рационе грубых частей растений увеличивает длительность пищеварения в первую очередь в рубце [36,38,39] [47] измеряли концентрацию спор B. anthracis в воздухе с наветренной стороны от старых почвенных очагов сибирской язвы, содержащих от 2•10 4 до 1,6•10 6 КОЕ/г почвы в национальном парке Этоша (Намибия) после механического воздействия на почву, имитирующего поднятие пыли при движении животных. При этом оказалось, что содержание спор на расстоянии 6-18 м от почвенного очага составляло не более 2 КОЕ/л воздуха.…”