wildlife diseases in greater yellowstone:

current problems, future threats and solutions that work

executive summary

What sets Jackson Hole apart from other spectacular and highly scenic mountain communities is its unparalleled abundance and diversity of wildlife. To the thousands of valley residents and the millions of visitors that come to Jackson Hole to experience the area’s offerings, it is the access to abundant wildlife that draws so many people to this remote location and pours millions of dollars into the local economy. It goes without saying that wildlife matters in and around Jackson Hole.

The wildlife conservation ethic that exists in Jackson Hole today is nothing new to the valley or state. Almost a century ago, settlers provided hay for starving elk in the wintertime and were instrumental in establishing the National Elk Refuge. Those early management efforts have evolved into a wildlife management strategy that includes feeding a total of 23,000 elk and 800 bison on the National Elk Refuge and 22 other elk feedgrounds in western Wyoming. Human feeding of wildlife has arguably led to artificially high wildlife populations in parts of Wyoming.

It certainly can be said that the early focus of wildlife management in the Greater Yellowstone Ecosystem (GYE) has achieved the intended success of assisting wildlife populations. But in the past decade, the results of key scientific studies have forced us to ask the key question: at what costs?

current problems: concentration and diseases

The legacy of wildlife feeding programs, such as those in western Wyoming, has artificially concentrated animals and created unnaturally crowded conditions that facilitate disease transmission. When presented with a readily available, artificial food source, elk and other wildlife alter their traditional migration patterns and change their natural behaviors. Elk feedgrounds are analogous to the crowded, unhealthy conditions that allowed the plague to spread quickly through Europe’s human population. For wildlife, brucellosis is an example of a disease transmission cycle that these conditions facilitate.

In all likelihood, brucellosis was brought to this continent by infected European cattle. It now affects elk and bison as an exotic disease in the GYE. Brucellosis often causes animals’ first pregnancies to end in abortion. Subsequent pregnancies are usually full-term and end in the birth of healthy offspring. The disease is spread by direct contact with the bacteria Brucella abortus, present in birth fluids and aborted fetuses.

The elk using western Wyoming feedgrounds appear to be most severely affected by brucellosis. When on artificial feedgrounds, elk do not isolate themselves for abortion events as they do under natural conditions, thereby potentially exposing hundreds of others to the bacteria. This artificial and feeding-induced behavioral change is the major mechanism that allows brucellosis to thrive on Wyoming’s feedgrounds. Indeed, scientific studies suggest that phasing out feedlots would ultimately – by itself – rid elk populations of this disease. Brucellosis is also present in bison populations; interestingly, most bison show few symptoms of the disease. While it is generally agreed that the elk and bison within the GYE represent the largest remaining reservoir of the disease in the U.S., brucellosis is not a threat to sustainable wildlife populations.

As such, most brucellosis research has focused on cattle. And while brucellosis vaccinations provide significant protections for cattle – with a few drawbacks – they are of questionable value for wildlife. Brucellosis garners a great deal of attention because of the possible threat of transmission from wildlife to livestock. Recently, there were only two states that did not have brucellosis-free status for their cattle, which is a significant issue in the livestock industry. Unfortunately in early 2004, Wyoming became the third such state after two herds were found to have the disease. Although possible, there have not been any confirmed transmission events from elk or bison to livestock in the wild. Feedlots, where elk are artificially concentrated, have much higher infection rates and may increase the risk of wildlife-to-cattle infection.

future threats

Chronic wasting disease (CWD) is one of the most serious diseases that could infect elk, mule deer and bison populations. CWD is in the same family of diseases as mad cow and the human version of mad cow, new variant Creutzfeldt-Jakob. CWD, like other diseases in its family, is fatal once contracted.

Scientists do not fully understand CWD progression or transmission. The infective agent that causes CWD and related diseases is not definitively known, but it is thought to be a malformed version of a brain protein called a prion. It is known that CWD moves readily through captive ungulate herds and kills all that contract the disease. Computer models to help predict the outcome of CWD outbreaks show that when infection rates are high enough to maintain the disease, populations become extinct. Game farms have the most severe outbreaks of CWD due to the close contact among animals.

CWD is endemic in 9.4 million acres in southeastern Wyoming and northeastern Colorado. The prevalence rates in this area vary by region and by species, but are relatively low compared to captive herds. Accordingly, this low infection rate among naturally dispersed animals most likely means that wildlife populations in these areas will not go extinct. In 2003, mule deer with CWD were discovered in both Wyoming and Colorado west of the Continental Divide, one of the barriers expected to contain the spread. The scientific community predicts that CWD will arrive within the GYE in a matter of time. The feedgrounds, including the National Elk Refuge, serve as quasi-game farms and may be the perfect enabler for CWD to gain a foothold in the region.

Because of its similarity to mad cow disease and its potential impacts to wildlife populations, managers in other regions have taken aggressive approaches to control CWD. When outbreaks occur, managers often decide to kill all deer and elk within a certain radius. While seemingly a sure-fire way to control outbreaks, this solution is problematic because the protein prion is very resistant and can infect wildlife that move back into an area. Further, this method kills wildlife that are genetically resistant to CWD, which may prevent wildlife populations from reducing or even eliminating the disease through natural selection.

Numerous other wildlife diseases pose a serious danger should they make their way to the GYE. The crowded conditions found on feedgrounds provide an ideal setting for the rapid spread of tuberculosis, paratuberculosis, pasteurellosis, scabies and others.

solutions that work

Disease is a natural part of any functioning ecosystem. However, diseases new to the ecosystem can have serious impacts to wildlife populations that have not had the evolutionary time to develop a natural immunity. Ridding the GYE of “native” diseases is neither realistic nor necessary. It is instead the challenge of 21st Century scientists and managers to protect our wildlife from new and potentially devastating disease outbreaks. An important first step must involve breaking the habit of artificially feeding our wildlife. Concentrating wildlife in that fashion promotes a cycle of wildlife disease, threatens cattle herds and perpetuates the near-perfect setting for new diseases to gain a stronghold in the Greater Yellowstone Ecosystem.