Notoedric mange is a disease that seems to be an increasing issue for bobcats in California (see 'Disease' page for more information about this disease). For me, this is a disease that is very interesting to study for several reasons. Prior to 2002, a mange epizootic (the equivalent of an epidemic for humans) had never been documented in any species of wild cats. In 2001, biologists with the National Park Service (NPS), working in Santa Monica Mountains National Recreation Area, observed their first notoedric mange case in a bobcat in the Thousand Oaks, CA. Lead NPS biologist, Dr. Seth Riley, was startled at what he observed for this bobcat (see photos below of bobcats with mange). Having studied bobcats for nearly 10 years by 2001, and never before observing a bobcat in this state, he was naturally shocked! He decided a veterinary pathologist was needed to diagnose what had happened to the bobcat. So, a pathologist with the Center for Animal Health and Food Safety performed a necropsy and ran a battery of tests on the bobcat. The pathologist found that the bobcat was extremely emaciated, was covered in notoedric mange mites, and after running a panel of potential toxicants the individual could be exposed to, found that it was exposed to high levels of anticoagulant rodenticides.
In 2002, a full-blown notoedric mange epizootic hit the bobcat population in Thousand Oaks. Over the next few years after 2002, more than 50% of radio-collared bobcats died of notoedric mange. Scat (fecal) surveys NPS performed along multiple fire road and trail transects in the same area mirrored the trend observed for radio-collared bobcats. Nearly 90% fewer bobcat scat was collected in the same area, confirming that during that time, the local bobcat populations were severely impacted. In recent years, since 2006, mange has been observed to affect multiple bobcat individuals and populations in Orange, Riverside, San Diego, Santa Barbara Counties and 3 other northern California Counties. There are two potential things occuring with apparantly increasing notoedric mange:
1) Because bobcats are elusive and difficult to study or observe, notoedric mange could be something that has affected their populations in the past but now we are more aware of the disease impacts because of biologists studying them in the State and because of increasing urbanization encroaching upon bobcat habitat.
2) Something is changing increasing bobcat susceptibility to the disease. This isn't necessarily one thing that could be different. Rather, it could involve multiple factors like higher bobcat population densities increasing opportunity for transmission of mange between individuals, potential stress from living near urban areas, increased opportunity to contract the disease from domestic cats, and exposure to toxicants like anticoagulant rodenticides. Bobcats are exposed to many factors in the wild, and there are also lot of unknowns for this disease that complicate the picture even more. For example, we are unsure whether bobcats always carry low mange mite numbers, or if it is a novel disease for them contracted instead from domestic cats- known carriers for the disease. It's possible that even the bobcat's prey items (woodrats, rabbits, or ground squirrels) are carriers of the disease! So, this makes the issue VERY difficult to study, and tease apart the many factors affecting bobcats!
Where Do We Stand On Understanding This Disease Now?
Notoedric mange has been one of the focal points and inspiration for my Ph.D. bobcat disease susceptibility research. I've been studying this issue for the past 6 years, and although some days I feel we are no closer to understanding this issue better, I have to keep things in perspective! First, research takes time. My research has required that I go out and design a project to study the issue, raise money to support myself and the research (as a graduate student at UCLA, I've been responsible to pay for ~85% of my research expenses, living costs, and tuition), trap bobcats to collect samples (including ones with the disease!), perform the lab work to get data from the samples and then analyze and write up a report about the data I collected. After 6 years on this path, and because of some of the samples I have and data I've collected, I've started collaborating with vets, epidimiologists, a gastroenterologist, and a toxicologist at UC Davis. Additionally, we have a vet and veterinary pathologist working for Department of Fish and Game now on the team to evaluate California bobcat health. Finally, we are increasing our communication with others studying bobcats across California to increase our opportunity for sample collection and monitor the state of other populations. This team we've assembled is a group of folks with varied expertise to help crack this problem. To start off, they have already recommended additional tests to run on the samples I've collected and are helping to interpret our findings thus far. Our team met last week at UC Davis, and we discussed what is known already and some data I and the state pathologist has collected on bobcats with notoedric mange.
Conclusively, we can still say that all bobcats that die with mange, whether in southern or northern California, are exposed to anticoagulant rat poisons. And, bobcats that are exposed to anticoagulants at greater than 0.05 parts per million residue concentration (measured in liver tissue) are 7 times more likely to die of notoedric mange! When they die, they are extremely emaciated. Some have evidence of anticoagulant toxicity, but anticoagulants are not the primary cause of death. One bobcat with severe mange that died while I was attempting to transport her to a wildlife rehab facility had a delayed clotting time (the mode of action of anticoagulants is to prevent the formation of some clotting factors essential to prevent uncontrolled bleeding). Most bobcats that die with mange have tarry-looking fecal matter (a sign of blood in the stool) and some have had blood in their stomach or intenstine. Both could be associated with anticoagulant toxicosis. Also, it seems there is no other disease that bobcats are first exposed to that is increasing their susceptibility to notoedric mange.
But why would anticoagulants increase bobcat suscpetibility to notoedric mange and how would it increase their susceptibility? That is what our new assembled team hopes to address!
One problem we are finding in dissecting available physiological health data collected from bobcats just before they died with severe notoedric mange is that they are so sick, it's hard to know whether what we are finding in these data is because of the anticoagulants or because of the disease. However, because we have some stored samples available from bobcats with mange, our bobcat health team is reccommending additional tests to try to tease these factors apart further.
Overall- the issue is very complicated, not the least bit straightforward, difficult to study under the best of circumstances. Some of the challenges that make this all the more difficult is a lack of information about notoedric mange and all the species it affects. We also have limited funds to run the tests we need to get more information both about healthy bobcats and those with notoedric mange and/or anticoagulant exposure. It would also be very helpful have a pathologist perform all of our bobcat necropsies, but since those cost $200/animal we biologists perform them ourselves and although we do our best, we are likely missing critical information that could help us understand this issue better.