Many insect-born diseases are on the rise, in part because of warmer winters associated with climate change. But Lyme and other tick-transmitted diseases are’t going to be controlled with ever more insecticides applied to the land, livestock and to our dogs and cats. We need to look at how farming, forestry and especially the activities state wildlife management authorities accord with the One Health concept that public health is in part dependent upon environmental/ ecological health.
The wildlife management practices of one representative state, Minnesota, and its Lyme disease incidence, provide a good example of the harmful consequences of ecosystem manipulations that increase deer numbers, coupled with the selective harvesting of other species that naturally help control Lyme disease by consuming ticks and rodents. In 2004, a record 1,023 Lyme disease cases were reported; this represents a 116% increase from the 473 cases reported in 2003.” My colleagues in the veterinary profession will attest to its increase in the canine population as well.
Small carnivores that help regulate the rodent population that is the major harbinger of Lyme disease are killed by the thousands annually including a recorded 1,012 Bobcats, 903 Fisher cats, 1,842 Martens, in 2010-2011, along with “a few thousand” Grey fox, up to 100,000 Red fox, over 44,000 coyotes and a few Mink and the Long and Short tailed weasels. Significantly, the number of licenses given out to trappers has risen from 925 in 1982-83 to 7,027 for the 2008-2009 season which parallels the rise in Lyme disease diagnosed in-state.
With an annual 450,000 deer hunters, some being permitted to kill up to 5 deer to depopulate some hunting zones, and smaller birds of prey which help regulate the population of rodent carriers of Lyme and other diseases succumbing to poisoning from ingesting lead shot in other prey and from the remains of hunter-killed deer, the small rodent population and attendant ticks are likely to flourish for decades to come. An astounding 1,300 tons of highly toxic lead shot is put into the environment by hunters every year. This accumulating poison gets into the food chain and has been found in Woodcock, and may be an issue in other ground-feeding, insect-consuming birds who play a significant role in controlling ticks, notably pheasants, grouse, turkeys, partridge and crows. Permitting hundreds of thousands of these tick-consuming birds to be killed annually by state licensed small game hunters is imprudent from a public health perspective.
Wild animals are the natural managers of healthy ecosystems. Putting animals and nature first in the science-based ecological management/stewarship of natural resources and wildlife is enlightened self interest and in accord with the One Health protocol. A re-assesment of current municipal, state and federal wildlife management and natural resource use beyond existing laws and policies is long overdue.
Recently completed ecological studies of the role of predators in controling Lyme disease confirm some of my assertions in a critical review “Crying Wolf’ at www.drfoxvet.com) of Minnesota DNR hunting, trapping and wildlife and habitat management practices. From the perspective of public health it would be prudent for the MN DNR to stop all trapping of small carnivores and to not continue with its proposed double hunting season and single trapping and hunting season for wolves.
Decline in red fox numbers due to coyote competition and predation are linked in this study to the increaed incidence of Lyme disease in the northeastern and midwestern United States. Recovery of wolf and cougar populations that help suppress coyote numbers may actually facilitate red fox population increse and thus greater control of Lyme disease carrying rodents, the primary prey of the red fox. (See Levi, Taal, et al. Deer, predators, and the emergence of Lyme disease PNAS 2012 ; published ahead of print June 18, 2012, doi:10.1073/pnas.1204536109 www.pnas.org/cgi/content.)
“Foxes, not deer, may hold key to rise in Lyme disease, study says”
By Amanda Alvarez, Journal Sentinel, Milwaukee Wisconsin June 18, 2012.
Increases in the deer population have been blamed for the explosion of Lyme disease cases in recent years, but changes in the numbers of foxes and coyotes - and what they eat - may actually be responsible, according to a study published Monday.
This could have implications for how wildlife is managed, and shed light on the complex ecosystems underlying the rise of Lyme and other tick-borne diseases.
Wisconsin saw a 280% jump in Lyme disease cases in the decade from 1997 to 2007, with a total of 2,376 cases statewide just last year. Other states in the Midwest and the East Coast have seen even greater increases. The bacterial infection that starts with a distinctive bull’s-eye rash can require extensive antibiotic treatment and may lead to arthritic and nervous system complications.
But what do small predators such as foxes and coyotes have to do with a disease spread by the deer tick?
The answer lies not only in the life cycle of the Lyme bacterium, Borrelia burgdorferi, but also in the ecological changes of all the animals with which it comes in contact. Normally, small mammals get infected by the bacteria, ticks get infected by feeding on the mammals, and then ticks feed and lay their eggs on deer. Foxes disrupt the chain by feeding on the small mammals.
“It was thought that deer were the only game in town for ticks,” said Taal Levi, lead author of the new study and a research fellow at the Cary Institute of Ecosystem Studies in New York.
Foxes have hunting habits that are different from those of coyotes: They will kill many small mammals at once, stashing the kill for later. Coyotes, on the other hand, especially those that have crossbred with wolves, will eat deer, rabbits, or even foxes, and are not efficient predators of small mammals the way foxes are. As coyotes have expanded in numbers and range, the new study suggests, they interfere with the important role served by foxes: to suppress Lyme disease rodent hosts, especially around human habitation.
The chain of events that leads to Lyme disease starts small, with a larval tick biting, say, a white-footed mouse that carries Borrelia bacteria. The tick matures into a nymph that can infect other animals each time it feeds. The life cycle of the tick typically ends with deer, on which they prefer to feed and lay their eggs. The unlucky outdoorsman or hunter may intrude at any stage and be bitten. Hunting, it turns out, was key to understanding the spread of Lyme.
Using harvest records from 1982 to the present, the researchers tracked the number of deer, coyotes and foxes in Wisconsin, Minnesota, Pennsylvania and Virginia. In all four states, coyote hunter harvests were up over the 30-year period, while fox harvests decreased.
Incidence of Lyme disease over the same time period mirrored the rise of coyotes and the decline of foxes. Deer abundance and Lyme cases were not related in Wisconsin, debunking the common belief that more deer equals more Lyme, according to the study, which was published in the Proceedings of the National Academy of Sciences.
There also was no consistent increase in Lyme with deer numbers in the other states. In fact, an area with a high fox population in western New York was notably devoid of Lyme.
A new picture was emerging, where Lyme appeared to be more closely associated with changes in predators rather than deer. Local survey data from the Wisconsin Department of Natural Resources helped to corroborate the hunter data. Deer observations were stable, even somewhat declining, from 1999 to 2009. The initial emergence of Lyme in the state may be linked to a deer boom in the 1980s and ‘90s. In the past 15 years, however, deer have waned while Lyme has continued its relentless spread. This more recent burst in Lyme prevalence appears to be linked to the statewide rise of coyotes and fall in foxes. Foxes don’t build dens where coyotes are present, and they may even be killed by coyotes. As a result, the small animals that host infected ticks are left to multiply freely.
Infectious disease emerging from altered predator-prey dynamics is nothing new; Levi points to bubonic plague and hantavirus as diseases whose spread also depends heavily on rodents and other common prey species. For Lyme research, shifting the focus from deer alone to the ecosystem underlying the disease has been challenging, says Levi, and perhaps overdue.
Jennifer Coburn, Borrelia researcher at the Medical College of Wisconsin, agrees: “These ideas fill an important hole in our knowledge of why Lyme disease is continuing to emerge. It’s not all accounted for by deer, who are dead-end hosts (for the bacteria).”
As the prevalence of other tick-borne pathogens increases, tracking wildlife numbers and transmission patterns may become even more important. Bacteria such as Anaplasma, and parasites like Babesia, are also spread by deer ticks. Last August, a new species of Ehrlichia bacteria was found in ticks in Wisconsin and Minnesota. While Borrelia, the bacteria that cause Lyme, can infect someone 36 hours after being bitten, Anaplasma can be transmitted from tick to human much more quickly. To stay on the safe side, Coburn advises meticulous tick checks every evening when returning from the outdoors.
Based on their research, Levi and colleagues suggest a deer reduction strategy be combined with efforts to rehabilitate the red fox, to reduce tick abundance and ultimately to stall the spread of Lyme disease. In fact, this may be already happening organically, as wolves recover and cougars move eastward. These top predators may control the coyote population, thus helping foxes recover.
Adrian Wydeven, an ecologist with the DNR, said wolf predation can also contain the spread of chronic wasting disease in deer, but he believes implementing the new study’s strategy of predator manipulation on a large scale would be very difficult.
Wisconsin already has proactive management of these animals in place, according to David Drake, wildlife specialist at the University of Wisconsin-Madison. The No. 1 goal of the harvest strategies is to ensure healthy populations of these species, with the aim of minimizing crop damage and threats to property from deer and predators.
Human diseases don’t figure high on the priority list: “I would not structure a deer season with the sole idea of reducing Lyme disease,” said Drake.
Rather, he views Lyme and other tick-borne maladies as a controllable public health concern, just not through wildlife management. The onus is on the individual, not the DNR, to manage ticks and, he said, “the public is aware enough of tick (avoidance) strategies.” Plus, “dogs and cats can bring ticks into the house, and you have a lot more interaction with your pets than with deer.”
Nebraska deer are in the throes of the worst outbreak of epizootic hemorrhagic disease in decades, according to the Nebraska Game and Parks Commission, with some 6,000 carcasses reported in 2012, compared with about 10 in 2011 and a 10-year high of several hundred. The disease is transmitted to deer via biting midges, which are thriving amid the state’s severe drought
* animaldocfox@gmail.com www.drfoxvet.net