Large predatory animals likely protect grazing animals from disease?

In the latest Jackson Hole News and Guide, outdoor writer Todd Wilkinson discusses the question, “Do wolves, cougars help curb diseases?” At the Wildlife News we have posed the same question. Properly stated this question can be investigated scientifically.

First a hypothesis (or hypotheses) need to be stated in a way that things can be observed and measured — which predators? Which grazing animals? Are there animals other than those that graze that are protected from disease?  What is meant by “curbing disease” or “protect?” Do we mean all diseases or just some of them? How do we measure “protection of” or “curbing disease?” What would not protected look like?

After the task above completed, then the actual data needs to be gathered. We suspect that overall these hypotheses are mostly true. It is important to remember that our suspicions are not observational evidence.

It might be difficult to find funding for this research, however. This is because current politics discourages investigation of these hypotheses because finding it true would cast doubt on the current predator management regime and also the way grazing wildlife is manged (such as winter feeding of many thousands of elk in Wyoming and other places).

Scientific research is currently being strongly attacked and misused in the United States by powerful interests and ideologies indifferent to verified facts, tested hypothesis, and the theories that result from them. We think current evidence tells us that large predators do retard the spread of many infectious diseases. The old statement that wolves mostly kill the weak and the sick appears to be true as a generalization. Critics of this seem to miss that it is a generalization similar to “tornadoes generally occur in the American mid-West.” This is true about tornadoes even though almost every state has some tornadoes. Likewise, wolves and cougars do sometimes kill strong, very fit elk, deer and the like. That happens when some other circumstance makes the weak and sick part not so important.

So let us see if we are correct or not, and in which ways. Scientific research in this matter must continue. We still believe that it is good to learn the truth, whether the truth supports our hunches or not.




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  1. Todd Wilkinson Avatar
    Todd Wilkinson

    I enjoyed your post, Ralph. Ah yes, alas, generalizations. And the next question is: why wouldn’t
    the desire for self persistence and survival pre-dispose predators to key in on the more vulnerable? The recognized prospect of being killed or disabled when taking on the strong and the better equipped for self defense is not lost on wolves. I’ve seen little evidence, and non convincing, that suggests otherwise. Have you? Indeed, natural systems are complicated.

    1. Ralph Maughan Avatar
      Ralph Maughan

      Todd emailed this to me, and I see he also posted.

      I replied this by email

      “I think it is almost certain that large predatory animals look for any advantage to exploit as they search for prey, whether it be age, size, injury, or simply whether they have a favorable location on the ground compared to their target.

      As to curbing disease, offhand, I think some competing hypotheses that need to be investigated are whether carnivores and scavengers also spread the disease after they have killed and consumed the prey or carcass. Do the predators themselves become infected?

      Oh, by the way. Would you add scavengers to the hypothesis?

      If they don’t become infected, I think knowing the mechanism for resistance would be really interesting.

      1. Scott Slocum Avatar

        Right, judgement is so much cheaper (and more profitable for fast talkers) than proof that we rarely ever learn the truth about complicated and lucrative things like this.

        But as for the adaptability of disease to any ecosystem, I’d guess that it’s unlimited; that some kind of disease will adapt to succeed in any type of predator/prey relationship.

      2. Ida Lupines Avatar
        Ida Lupines

        Do the predators themselves become infected?

        This is something I wonder about too. It would seem we need predators. Great post – I look forward to more information on this!

    2. ramses09 Avatar

      Wolves hunt to eat – humans hunt for the fun of it. Wolves do take the sick, old, damaged species,humans take the biggest & the most beautiful of species.

      Thanks for another great post Ralph!

  2. Richie G. Avatar
    Richie G.

    The only way I can see it being the other way around if their are a great number of wolves on the attack and if they are desperate I mean very hungry not have eaten for a very long period of time.

  3. Mark L Avatar
    Mark L

    I don’t see this being provable through wolves (or other large ‘charismatic’ …or uncharismatic) predators, but through water bourne predators or unexpected sources like rattlesnakes or spiders. Too politically charged to show the obvious here…suggest a flanking move? I do think it has merit though. Would love to see pre K/T evidence …i.e. Dinosaur fossils.

  4. Richie G. Avatar
    Richie G.

    I seen a picture of MOOSE who had to calves bedding down behind somebodies house ,I am sure it took place in Alaska. Now a Grizzly bear approached in the morning. Won’t go into the details but the Grizzly killed both calves. The commentator said the bear would be killed cause he was too close to people. So here is a bear going after an easy kill, so why would not many predators do the same thing in the wild. IT’s been filmed wolves and other predators going after babies, lions too with water buffalo.

    1. ramses09 Avatar

      I know it’s nature but still sad 🙁

  5. Larry Thorngren Avatar

    I can remember lots of photos of wildlife researchers breaking open bones of dead deer to show from the red marrow that the deer starved to death.
    It would seem that similar studies could be done on the fringes of the areas infected with CWD by doing brain and spinal cord studies on wolf and cougar killed deer and elk to see if these predators are selecting for the CWD diseased animals.
    I am sure there are lots of wannabe wildlife researchers that would work for board an room + gas as interns.
    Yellowstone seems to be full of them.

    1. Jay Avatar

      That is, if you can find them among the hoards of wannabe wildlife photographers.

  6. Richie G. Avatar
    Richie G.

    Most of the people who write on this website excluding me really know how to do research in the wildlife field and many have their Masters or PHD’S IN wildlife I have learned a great deal just by reading their comments. I would guess most of these questions have already been answered.

  7. George Swan Avatar
    George Swan

    This is an interesting question and Richie’s right there is a decent body of literature already out there on this subject. The paper below is a good example.

    “Keeping the herds healthy and alert: implications of predator control for infectious disease” Packer et al., 2003 Ecology Letters

  8. Richie G. Avatar
    Richie G.

    people are lucky that their are people who want to take pictures of wildlife with all the abuse the animals go through and I would Imagine it’s out west too! . Illegal vets take the vocal cords out of pit bulls so nobody will hear them fighting or better yet if the cops raid a drug house they will not hear the dogs, so thank God for small favors!

  9. CodyCoyote Avatar

    Back at the dawn of Wolf reintroduction c. 1995 , there was also a small outbreak of Chronic Wasting disease in NW Wyoming. A couple of deer were found to be suffering CWD in the Owl Creek Mountains west of Thermopolis 75 miles south of Cody. Game and Fish got very concerned.

    Coincidentally , there came into that region a pack of the wolves, some of the first to disperse out of Yellowstone. They came to be known as the Washakie Pack and roamed all the way over to the DuNoir River above Dubois and back around to Meeteetse country.

    A year or so later it was determined there were no more deer infected with CWD in the Owl Creeks. And none since.

    Am I saying the wolves took care of the weak and sick CWD deer? No. I have no direct evidence of that. But the timing is serendipitous, plus the fact the southern Big Horn Basin and Owl Creeks have a substantial Cougar population , and the big cats feed almost exclusively on deer.

    Make of it what you will. Multiple Deer appear with CWD in an area enjoined with two major predators , then there is no more CWD reported there in fifteen years.

    Back about 2006 at a public forum on the pending wolf management plan in Cody , I asked the Game and Fish’s top man there if the department saw any positive value to wolves at all. That supervisor, Bill Rudd, said no. Then I rephrased the question and told the story about the Owl Creek CWD deer and the Washakie wolf pack, and asked him if it was possible the wolves took care of the CWD there. He ducked the question. Wouldn’t go there. Started to get a little red in the f ace and his jugular was distending and throbbing. he simply could not bring himself to take back his statement that wolves have positive ecological uses. He just could not bring himself to say it , and lose face . But I think he was thinking it…

    1. ramses09 Avatar

      Sounds like Bill Rudd needs to start reading more & believe in science – ALL of those folks out west should just open their minds to it.
      Obviously an anti-wolf guy.

      1. CodyCoyote Avatar

        AT the time I believe Bill Rudd was the senior Wyo G&F manager in charge of Trophy Game.

        I took him at his word and he was speaking on behalf of the Department when he flatly stated Wyo G&F saw no positive value to having Grey Wolves back in the region. I beleive he or someone standing next to him also stated the Department was in the camp that ” wolves were foisted on Wyoming by the Feds” or something along those lines. Nearly unanimously I would add… I have yet to hear a single Wyo G&F person —even Marc Bruscino the recently retired wolf and grizzly wrangler who was on the team that brought the wolves down from Canada in ’95 and again in ’96 — state that wolves have a positive ecological value as wildlife in the ecosystem.

        I have heard US Fish & Wildlife Service personnel say wolves are beneficial.

        It will be nigh impossible to do any definitive research that large predators are disease modulators. So having only anecdotal evidence, hunches, and ” thought experiments” to go on , those who are anti-wolf can come to the fray heavily armed with silver bullets of Barstool Biology Bullsh_t.

        1. Louise Kane Avatar
          Louise Kane

          This comment is for JB and relates back to our earlier discussion about fish and wildlife/ fish and game or wildlife agencies being corrupted. I would ask, when a senior manager of a fish and game office sees absolutely no value in a top predator, isn’t that corrupt? broken, unstable even? What has changed in the last hundred years – less poison?

          Cody’s comment is an example of what I was talking about.

    2. Ralph Maughan Avatar
      Ralph Maughan

      Cody Coyote,

      I remember the Washakie Pack, and the opposition is somehow gathered. At the time I said the pack is probably doing more to save the numerous deer in the area than anything humans would do.So, I am especially glad to get your historic update.

  10. ramses09 Avatar

    Very interesting story by the way CodyCoyote, thanks for sharing it.

  11. Mark L Avatar
    Mark L

    Some interesting work on this by Sean M. Moore, Elizabeth Borer, and Parviez Hosseini from 2009.

  12. Mike Bickley Avatar
    Mike Bickley


    Or maybe CWD is the result of the absence of large predators for 70 plus years.

    1. CodyCoyote Avatar

      … except the area where the Deer with CWD were found back in 1997-98 is an area loaded with Cougars , who eat primarily deer for prey, and are also heavily hunted by the human, hound , and snowmobile packs . Cougars have always been prevalent thereabouts. I’m think that introducing wolves that hunt in packs, tactically , may have been a new variable in the ecology equations.

  13. Todd Wilkinson Avatar
    Todd Wilkinson

    Folks: Great discussion. Thanks CodyCoyote for the story. Here is something that Ralph brought up with me earlier in an email: the frightening possibility of CWD infecting predator populations. So far no evidence to suggest it has passing across the species divide but in recent days I’ve received emails from several folks who have expressed this concern, including someone who is convinced that BSE, which caused the Mad Cow scare in Britain, has shown up in domestic dogs. The issue has been examined and so far not a lot of hard evidence to prove it is so.

    1. SAP Avatar

      I’m a little rusty on my understanding of prion diseases like Chronic Wasting Disease (CWD), but it’s instructive to look back at the British trans-species BSE (Mad Cow) outbreak.

      Basically, an animal with a TSE (transmissible spongiform encephalopathy) starts out with relatively few of the mis-shapen proteins called prions. The prevalence of prions in the animal grows tremendously as the animal lives with the disease. Prions are concentrated in the central nervous system, but can occur in any tissue or blood.

      Many of the cattle that get ground up for burgers are older dairy cows. Burger — at least back then — also used to contain a lot of ground up spine and maybe some brain. So, get a burger made from elderly dairy cows, and you’re getting a potentially whopper dose of prions. (And prions, not technically alive, aren’t rendered ineffective by cooking.)

      Apparently, during the UK Mad Cow outbreak (the disease in humans is called variant Creutzfeldt-Jakob, or vCJD), Britain’s meat supply had a tremendous amount of prions in it (a combination of the cattle feeding practices of the time, along with meat processing that included lots of central nervous tissue, and maybe the food culture of the UK as well?)

      Yet, even considering long incubation time for vCJD, infection rates from eating prions in beef are low (177 vCJD deaths between 1986 and now).

      In other words, even if you eat really really heavily infected animals, it’s not certain that you’ll come down with a TSE yourself (not trying to make anyone feel ok about eating prions, of course, and I don’t feel USDA is doing enough to protect us here). Speculation is that our own digestive acids render the prions ineffective. Supporting this notion, pigs (who can get TSEs if you put prions directly in their brains) can eat nasty prion-laden stuff steadily yet never get infected.


      So what? Pigs aren’t wolves, of course. But let’s go back to that point about prions increasing greatly as the infected animal lives with the TSE. With predators around, a wild ungulate that is even a little bit compromised by a TSE (such as CWD) is going to get picked off pretty rapidly, probably pretty early in the disease’s progression.

      In livestock, heavily infected animals can’t even walk. It’s extremely unlikely that a wild ungulate almost anywhere could get to that point, especially in an environment with large carnivores. It seems safe to assume that infected animals would get killed pretty early on.

      The upshot: if a wolf or a bear or a cougar kills and eats a CWD-infected animal early in the disease’s progression, it’s probably getting a relatively light dose of the infectious agent, the prions. It’s not the same as a person eating a burger with a bunch of prion-laden spinal cord from an 8-year-old BSE-crippled Holstein in it. And if it’s indeed true that stomach acids* protect us from prions, then there’s a good chance that what prions they do eat will be ineffective (again, considering the level of prions in the UK beef supply in the 1980s, it’s clear that far more people were exposed to prions than were infected).

      Sure, I’m biased (I like large carnivores). But I’d say, large carnivores are highly unlikely to spread CWD by getting infected themselves. More likely, by removing infected prey animals early on, and by cutting down on large, sedentary concentrations of ungulates, they’ll play a big role in containing CWD (if we let them . . .)

      *On the role of stomach acid: fascinating 2011 study here, where they gave mice Prilosec (the heartburn drug) to reduce their stomach acid, and fed them prions. The mice that got Prilosec developed brain infections at more than twice the rate of the control mice.

      1. Nancy Avatar

        So SAP, after venison chili or elk burgers, probably not a good idea to toss back Prilosec or a couple of Tums? 🙂

        A link to some articles about CWD but you can’t freely access them:

        The dieoff of over 400 deer around Missoula this past fall due to CWD, should of been a wake up call but I’ve seen little about it since. I would think those that claim wild game is the only way to go when it comes to meat, would be concerned.

        1. SAP Avatar

          Somehow missed hearing about any CWD outbreak in Montana? Are you sure that wasn’t hemorrhagic fever or bluetongue? Most recent sources still indicate no CWD in Montana.

          Along with willy-nilly over-prescribing of psychotropics, the widespread overuse of acid-suppressing drugs is a dangerous trend. A lot of people with “acid reflux” should look first to moderating their diet and sleeping habits, instead of dialing down one of their bodies’ front-line defenses against pathogens. But we’re a nation of overgrown children: if Larry the Cable Guy is telling everyone they can drink beer and eat chili dogs with wild abandon — all you gotta do is take this little pill!! — we literally eat it right up. Can’t be a downside if Larry the Cable Guy (MD?) says it’s the way to go!

          1. Nancy Avatar

            Oops, Hemorrhagic it was SAP.

            But how long before CWD shows up here?


            1. Elk375 Avatar

              They just have not found it yet.

          2. Mark L Avatar
            Mark L

            On SAP’s comment:
            After those acid-suppressing drugs ‘leave’ our bodies, think about where they go. They are still suppressing acid, too. Same with anti-bacterial soap after we use it and medicines too (heart disease, birth control, blood thinner, etc.).

        2. Elk375 Avatar

          To my knowledge there has only been one case of CWD in Montana. An elk was found infected in a captive elk herd in Phillipsburg, Montana many years ago. The entire herd was destroyed.

          The deer that died around Missoula was not from CWD.

  14. Gary Humbard Avatar
    Gary Humbard

    Lyme disease has vaulted to the rank of the fastest-growing infectious disease in the U.S. The disease is passed more by the little nymphs that sip blood from chipmunks and mice although the disease is also spread by ticks on deer. Deer, mice and chipmunk populations (especially on the east coast and midwest) have skyrocketed because of the dramatic decrease of predators.

    Because of the huge increase in deer and higher human densities, hunters cannot effectively reduce deer populations, however predators such as coyotes could do the job if given the chance.

    1. Immer Treue Avatar
      Immer Treue

      And foxes, if they were not incessantly trapped, to reduce the white footed mouse population.

    2. Scott Slocum Avatar

      Gary, you jumped really quickly from small rodents to deer, so I’m not sure what you meant about controlling deer; but we do have a couple of good control measures available for deer who live in areas of high human density: 1) don’t feed the deer, and 2) special hunts. Coyote depredation on deer isn’t an option in any suburb or city that I know of.

      1. Gary Humbard Avatar
        Gary Humbard

        Scott, the areas I was referring to are in the countrysides near towns and cities where predators such as coyotes and foxes can still inhabit if given the chance. Overpopulation of deer is causing native plants to be overbrowsed resulting in the invasion of non-native species. Hunting brings problems (ie. discharging firearms near humans, accidents, enforcement) that predators do not. In regards to efficiency, predators are much more efficient than humans since they must eat to survive.

        Coyotes in California have been found to prey on house and feral cats which has resulted in dramatic increases in songbirds, lizards and other native species. House and feral cats kill hundreds of millions of birds each year.


Dr. Ralph Maughan is professor emeritus of political science at Idaho State University. He was a Western Watersheds Project Board Member off and on for many years, and was also its President for several years. For a long time he produced Ralph Maughan’s Wolf Report. He was a founder of the Greater Yellowstone Coalition. He and Jackie Johnson Maughan wrote three editions of “Hiking Idaho.” He also wrote “Beyond the Tetons” and “Backpacking Wyoming’s Teton and Washakie Wilderness.” He created and is the administrator of The Wildlife News.

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