Possible bighorn disease strategy

Strategies to combat sickness in bighorn sheep show promise

Cassirer, who has spent her career at the forefront of research attempting to understand the disease that is passed to wild sheep from their domestic cousins, is leading a study to see if intervention from wildlife managers can shorten the time it takes for bighorn populations to recover from initial infections.

The study revolves around identifying and removing the bighorn equivalents of Mary Mallon. The cook, better known as Typhoid Mary, was quarantined by New York health officials in the early 1900s after she was identified as a carrier of typhoid fever.

Cassirer said when pneumonia first hits a bighorn herd, it is passed from sheep to sheep, often killing many of them. Those that survive become immune, but the disease doesn’t go away.

“We think once it gets into a population it’s the females that keep it there. We think the ewes get some immunity and the lambs don’t,” she said. “The (ewes) that don’t die, they not only get immunity, they get rid of the pathogen. But some are like Typhoid Mary; they get immunity but they carry the pathogen.”

A carrier can infect her lamb, which then has the ability through play to pass the sickness to other lambs.

She said the herds don’t completely recover until the carriers die off.

Cassirer is trying to determine if wildlife managers can shorten the recovery time by taking the same tack that New York health officials did with Mallon 100 years ago — removing the carriers from the rest of the population.

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I know in those circles this has been widely discussed but implementation of it has always been a giant, insurmontable hurdle. Speaking as a guy who hunted the Tendoys some 60 days in two years and never got a sheep, how would you do that for an entire herd?

Interesting idea if it does indeed prove to be effective, but I have a hard time seeing how they would be able to pull this off for every outbreak. It seems that it would be exceedingly labor intensive and expensive to do. I suspect funding will be the limiting factor for agencies who might look to adopt this strategy. Wonder what avenues might be available to help cover the costs for something like this?

Not only funding but some of the terrain they inhabit would be nearly impossible to navigate for trapping an entire herd.

It's a short term solution if wild sheep continue to have contact with domestic sheep.

I don't even think that this is a short term solution, because managing wildlife in this capacity is not an easy, quick fix. I also feel that if people are focusing on this type of intervention, they keep ignoring the domestic cause.

This has actually been done several times in Colorado as part of an experiment. So far, results are encouraging. Once the slate is cleaned (so to speak), it's amazing how fast a unit can bounce back after years of little/no lamb recruitment. As pointed out, the ability to clean that slate can sometimes be difficult. Bait sites in the winter are extremely effective at taking care of that hurdle.

Keep in mind that this is not a cure all for the issues our wild sheep face. If the right situation presents itself to wildlife managers, it can be a beneficial tool. Solving for domestic interactions with wild sheep (almost impossible) and finding a cure/vaccine probably hold broader and longer lasting positive impacts for the health of our sheep herds.

Oak could probably interject with more details. I'm more of a lurker and don't usually post.

The strategies that L4MH and the OP are discussing are different. Dr. Cassirer (and others) are exploring the possibility of removing "super-shedders" from the herd only...those infected ewes that persist after a disease event and sporadically shed bacteria, resulting low or no lamb recruitment. As pointed out by some, it's not a solution to the disease issue and a matter of ignoring the domestic separation problem. Rather it's a way to potentially speed up recovery of herds that have suffered respiratory disease events. One thing that would make this strategy of speeding recovery more feasible is a field test that would allow managers to identify carriers of the bacteria while they had the sheep in hand, which would allow them to lethally remove positive sheep. The RMBS has recommended Auction and Raffle account funding the last two years for development of a rapid PCR method for detecting pathogens in live sheep, which can be performed in a field setting with minimal equipment, and which provides results in less than one hour. Progress on this project is very promising, and hopefully managers will have this tool in their kit in the near future.

What L4MH is referring to is similar and related, but in those cases managers removed all sheep from remnant bighorn herds that consisted of less than 20 individuals and had zero lamb recruitment for several years. This was done in conjunction with a density-dependence study to assess whether low lamb recruitment may be driven by density-dependent mechanisms, and thus whether reducing bighorn density will increase lamb recruitment. Two replications of the study were performed, with the second replication ongoing. These research projects were also funded by A&R money and RMBS funds. Once the remnant herds were removed, bighorns were introduced from large populations where managers suspected that density may be suppressing lamb recruitment. Recruitment among the collared ewes in the control herd where sheep were removed was compared to recruitment in the reintroduced herds. I don't want to comment on results until the research is published, but the reintroduced herds are doing outstanding.