Dr. Michael W. Fox

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Lyme Disease and Wildlife Management


LYME DISEASE PREVENTION AND WILDLIFE MANAGEMENT:


A ONE HEALTH PERSPECTIVE


By Michael W. Fox BvetMed, PhD, DSc, MRCVS


                             


The One Health concept that human, animal and ecosystem health are interconnected, adopted by the American Medical Association, American Veterinary Medical Association and other health organizations (1) (www.onehealthinitiative.com and www.onehealthcommission.org ) is becoming a significant movement since its acceptance as a resolution by the National League of Cities (2) (www.nci.org/influence-federalpopicy/resources). An illustrative review presented below applies this One Health concept to a public health issue in Minnesota that is relevant to all states and countries where Borreliosis (Lyme disease) and other insect-transmitted and animal-harboring diseases are an increasing public health concern (3). It will show how this health issue is connected to human activities variously condoned and legally protected by local and state authorities, the Department of Natural Resources in particular, and some evidence based public health proscriptions and initiatives are considered. Ecosystem manipulations that increase deer numbers, coupled with the selective harvesting of other species that help control Lyme disease by consuming ticks and rodents, are of particular concern.


As in other regions across the U.S., the ‘wilderness’ and wild lands of Minnesota are in various stages of recovery following two centuries of  unregulated human exploitation, from logging and mining to farming, hunting and trapping. Now under the banner of the nascent One Health movement, the dots are being connected between Lyme disease and other public health concerns and healthy ecosystems and wildlife (4,5) This calls for a re-assesment of current state and federal management and protection of natural resources beyond current laws and policies advocating “sustainable” natural resource use. In particular, the encouragement (but not enforcement) of ‘best’ farming and ranching practices, monitoring of recreational activities such as hunting and commerical  trapping by setting seasonal quotas, call for a new approach from the One Health pesrpective.


Lyme Disease Epidemiology


The Minnesota Department of Natural Resources and the Pollution Control Agency have sufficient data (see below) to connect the dots with the Minnesota Department of Public Health’s (MDPH) alarm bell report of an escalating incidence of Lyme disease in the human population,(6) stating that: “Record numbers of Lyme disease cases were reported to the Minnesota Department of Health (MDH) in 2004, including substantial numbers of case-patients exposed to infected Ixodes scapularis ticks (deer ticks or black legged ticks) in some western and central Minnesota counties not previously considered high risk areas. Other diseases transmitted by I. scapularis namely human anaplasmosis, (HA, formerly known as human granulocytic ehrlichiosis or HGE) and babesiosis, were also reported at record or near-record levels.--- Since MDH began Lyme disease surveillance in 1983, 5,833 cases of Lyme disease (agent, Borrelia burgdorferi) have been reported among Minnesota residents. In 2004, a record 1,023 Lyme disease cases were reported; this represents a 116% increase from the 473 cases reported in 2003, and an 18% increase from the prior high of 867 cases in 2002. As recently as 1999, Lyme disease incidence was 6.0 per 100,000 Minnesota residents, versus the 20.0 per 100,000 observed in 2004.” It is also notable that more cases of Lyme disease in dogs are being diagnosed by veterinarians in Minnesota (7). This Blacklegged or Deer tick feeds primarily on small rodents during its larval stages of development, moving to larger species, notably deer, as reproducing adults. In contrast the winter tick Dermacentor albipictus spends all stages on its primary host, deer and moose, often causing severe anemia and endangering the latter species in Minnesota. Adult females fall off in April to lay eggs on the ground and are then vulnerable to ground-feeding insectivorous birds, the primary hosts being free of these ticks after late May.


DEER CONNECTIONS


The MN DNR’s management of the White tailed deer population is challenging because high-density populations in some hunting zones can mean high tick numbers, (8) especially when wolf predation on sick and debilitated deer is disrupted or negated by hunters and trappers killing these natural deer-herd managers. Some 250,000 licensed deer hunters in 2011 were permitted to kill up to 5 deer to depopulate some areas.  This widely quoted figure refers to the estimated seasonal number of actual deer hunters, but may be a low figure considering that in 2011 there were 192,331 registered deer kills, with a combined total of licenses sold for regular firearms, archery and muzle loaders reported to be almost 760,000. (The MN DNR manages a reported 110 game species on 1.1 million acres, generating over $25 million from the sale of hunting and trapping licenses in 2008).


 Several studies have shown that abundance and distribution of deer ticks are correlated with deer densities (9). When the deer population was reduced by 74% at a 248-acre (100 ha) study site in Connecticut the number of nymphal ticks collected at the site decreased by 92%.The relationship between deer and tick abundance, and human cases of  Lyme disease was documented in the Mumford Cove Community in Groton, CT, from 1996 to 2004. The deer population in Mumford Cove was reduced from about 77 deer per square mile to about 10 deer per square mile (4 deer per square kilometer) after 2 years of controlled hunting. After the initial reduction the deer population was maintained at low levels. Reducing deer densities to 10 deer per square mile (4 deer per square kilometer) reduced the risk of humans contracting Lyme disease in by more than 90% (10).


 But reducing the deer population in small areas may lead to higher tick densities resulting in more tick-borne infections in rodents leading to a high prevalence of tick-borne encephalitis and creating a tick “hot-spot” (11). This finding confirms the importance of DNR management practices encouraging thriving populations of smaller carnivore species to help control rodent numbers, especially as a ‘buffer’ when there is over-harvesting of deer in some hunting zones and seasons.


RODENT AND CARNIVORE CONNECTIONS


The probability of more people and their ‘litmus’ dogs becoming infected increases with the more there are of  tick infested  rodent species that harbor this, and other diseases in the environment that these people inhabit or visit. In one field study it was reported that “the strongest predictors of a current year's risk of Lyme disease were the prior year's abundance of mice and chipmunks and abundance of acorns 2 y previously. In no case did inclusion of deer or climate variables improve the predictive power of models based on rodents, acorns, or both” (12)


 When the carnivorous avian and mammlian predators that keep rodent numbers in check are being killed by trappers and hunters, and in some states also by diseases transmitted by free roaming cats and dogs, rodent numbers will increase. Rodents are not on the DNR’s radar for ecosystem management, otherwise we would most likely not have this escalating public health problem, the environmental effects of climate change/global warming (13) not withstanding.


The probability of escalating tick-born diseases in Minnesota, and most likely therefore in other states where Lyme disease and other tick born diseases are prevalent, is supported by the high annual carnivore mortalities from trapping recorded by the MN DNR, some 1,012 Bobcats, 903 Fisher cats, and 1,842 Martens, whose main diet is small rodents, being killed by licensed trappers in 2010-2011. The DNR also states:


 The gray fox is classed as a furbearer, and is managed with a regulated hunting and trapping season each year. Only a few thousand are taken for fur annually. Information not posted by DNR---.The red fox is the most common predator in the state. Hunters and trappers harvest up to 100,000 each year, but the fox population remains strong. ---Coyotes can be harvested by hunting and trapping. In Minnesota, roughly 4,000 are shot or trapped each year.”


But in another set of figures for 2010-2011 the DNR reports the killing of 44,051 coyotes by small game hunting license holders. In addition, government predator control agents exterminate ‘troublesome’ coyotes, on which there are now bounties in some counties, and trap and kill an average 200 problem wolves annually. All these predator species are the main rodent population control agents in healthy, well-managed ecosystems, along with Mink and the Long and Short tailed weasels who are also prey to trappers. 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.


What will be the long-term ecological impact of the DNR’s annual kill quota of a provisional 400 wolves following a permit lottery for 6,000 wolf hunters and trappers who are likely to catch non-target endangered species such as the Lynx as well as other smaller carnivores? Couple this with over 7,000 licensed trappers already having permits for other species, the small rodent population and attendant ticks are likely to flourish for decades to come. Lyme and other tick born diseases will predictably escalate in the human population.


In a telephone survey that I conducted on Feb 8th 2013 of taxidermists serving hunters and trappers across Minnesota there was a consensus that the dramatic increase in coyote numbers over the past decade was responsible for the no less dramatic decline in red fox numbers. I also learned that feral cats, frequently caught in traps and prevalent in many areas, may contribute significantly to the demise of ground nesting and other insectivorous birds.


Avian Connections


Smaller birds of prey also help regulate the population of rodent carriers of Lyme and other diseases, but many succumb to poisoning from ingesting lead shot in other prey and from the remains of hunter-killed deer. According to a 1999 report by the Minnesota Pollution Control Agency, some 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, paralleling the accumulation of mercury from the state’s coal- fired power plants which contaminate fish in the great lakes, children and other consumers. Lead has been found in Woodcock, and may be an issue in other ground-feeding, insect-consuming birds that play a significant role in controlling ticks, notably pheasants, grouse, turkeys, partridge and crows. Permitting hundreds of thousands of these birds to be killed annually by state licensed small game hunters may be imprudent from a public health perspective.


 HUMAN CONNECTIONS


Urbanization and other anthropogenic factors can be implicated in the spread of the Lyme disease organism ( Borellia burgdorferi sensu lato) to humans (14). Human interferences and practices that do not foster optimal biological diversity in ecosystems, (such as the rattle snake roundups in the South West), cause rodent population imbalances. These are associated with incresed incidence of various zoonotic (animal-to human) diseases such as documented outbreaks of Sylvatic plague and Hanta virus in the U.S. southwest. Rodent populations can also harbor leptospirosis and tularemia, carry other tick-born diseases such as Tick paralysis, Rocky mountain spotted fever, Colorado tick fever, and Ehrlichiosis, and be the reservoirs for mosquito transmitted St. Louis, LaCrosse and California encephalitis viruses, Eastern and Western equine encephalitis and West Nile fever. Municipal, agricultural and wildlife/natural resource management activities that disrupt terrestrial and aquatic ecosystems and consequentially reduce indigenous populations of insectivorous birds, bats and other veretebrates and invertebrate species that variously help control tick and mosquito numbers, give an anthropogenic edge to the emergence of zoonotic diseases. Notable are two studies that underscore the Lyme-disease promoting consequences of human depredation on carnivores that indirectly control this disease be reducing rodent numbers and which should lead to tighter restrictions and prohibitions of hunting, trapping and poisoning. ( !5, 16).


CONCLUSIONS


The evident fostering of high deer densities as a form of wildlife farming by the Minnesota DNR, compounded by the deers’ access to agricultural land to feed on corn and other crops, coupled with decades of harvesting and near extermination of small and large carnivores, lead from hunters’ shot poisoning raptors and ground-feeding birds being killed in large numbers by licensed small game hunters, has created a perfect ecological storm for the proliferation of Lyme and other disease- transmitting ticks. The same is probable in other states following the same cultural traditions and imperatives of hunting, trapping and predator control.


The science-based ecological and ethical management/stewarship of natural resources and wildlife is in accord with the One Health concept. Since healthy ecosystems interface with public health, all state, federal and private business activites that adversely impact the functional integrity of the natural environment need to be called to question from the enlightened self-interest perspective of One Health. The control and prevention of endemic zoonotic diseases and new emerging diseases that threaten both the human and domestic animal populations call for an inter-agency and inter-disciplinary approach with public involvement (17), the effectiveness of which would be enhanced by a shared vision of the One Health concept (18)


 Such a vision shared by the veterinary and medical professions and allied specialists in epidemiology, conservation biology and other sciences calls for a diplomatic and ultimately collaborative engagement with other stake holders and responsible parties including: state and federal regulatory agencies, politicians, legislators, the business community, farmers and hunters, non-profit conservation and animal protection organizations. A civil society initiative to examine how natural resource and wildlife management practices can help play a critical role in the reduction and prevention of zoonotic diseases such as Borreliosis (Lyme disease), along with improved protection of predator species, is long overdue.


 

 ADDENDUM

The U.S. government’s Centers for Disease Control & Prevention reports that each year, approximately 30,000 cases of Lyme disease are reported to them by state health departments and the District of Columbia. However, this number does not reflect every case of Lyme disease that is diagnosed in the United States every year. This is estimated now to be around 300,000 people diagnosed with Lyme disease annually.

 

 The number of tick-borne illnesses reported to the U.S. Centers for Disease Control and Prevention is on the rise. Lyme disease leads the pack. In the Northeast, the black-legged ticks (Ixodes scapularis) that spread Lyme disease also infect people with other maladies, among them anaplasmosis, babesiosis, and -- as a new paper in the journal Parasites and Vectors reports -- Powassan encephalitis.

 

 Powassan encephalitis is caused by Powassan virus and its variant, deer tick virus, recently identified in New York state. The virus is spread to people by infected ticks, and can cause central nervous system disruption, encephalitis, and meningitis. There is a 10-15% fatality rate in reported cases, with many survivors suffering long-term neurological damage. Unlike Lyme disease, anaplasmosis, and babesiosis -- which take feeding black-legged ticks hours to transmit --Powassan deer tick virus transmission can occur in just 15 minutes. This leaves very little 'grace period' for removing ticks, and underscores the importance of vigilance in tick habitat.


Since 2006, reports of lone star ticks have been steadily increasing in Wisconsin, and University of Wisconsin-Madison entomology professor Susan Paskewitz suspects there may be thousands of the ticks in well-established populations that are able to survive the winter. The tick carries ehrlichiosis, a zoonotic bacterial disease, which may also confer a certain type of beef allergy in rare cases!


 


 


References


(1) (www.onehealthinitiative.com and www.onehealthcommission.org )


(2) www.nci.org/influence-federalpopicy/resources)


(3) Collinge S K, Ray C.  Disease ecology: community structure and pathogen dynamics Oxford, UK: Oxford University Press.2006.


(4) LoGiudice K, Ostfeld R, Schmidt K, et al. The ecology of infectious disease: effects of host diversity and community composition on Lyme disease risk. Proc Natl Acad Sci USA 2003; 100: (2): 567–571. 


(5) Keesing F, Holt R D, Ostfeld R S. Effects of species diversity on disease risk. Ecol. Lett 2006; 9:485–498


(6) The Minnesota Department of Health Disease Control, Dramatic increase in Lyme disease and other tick-borne diseases, 2004.  Newsletter May/June 2005: Volume 33, Number 3 (PDF).


(7) Robertson T. Tick-borne diseases on the rise in northern Minn. MPRNews Aug 3, 2011.


(8) Wilson M L, Ducey AM, Thomas S, et al. Microgeographic distribution of immature Ixodes dammini ticks correlated with deer. Med & Vet Entomol.1990; 4: 151–159.


(9) Kilpatrick HJ, LaBonte AM. Managing urban deer in Connecticut: a guide for residents and communities (2nd ed.). Connecticut Department of Environmental Protection. http://www.ct.gov/dph/lib/dph/urbandeer07.pdf. 2007. 


 


(10) Rand PW, Lubelczyk C, Holman MS. et al. Abundance of Ixodes scapularis (Acari: Ixodidae) after complete removal of deer from an isolated offshore island, endemic for Lyme disease. J. Med Entomol 2004; 41; 779–784


(11)   Perkins SE, Cattadori IM, Tagliapietra V, et al. Localized deer absence leads to tick amplification. Ecology 2006; 87: 1981–1986.


(12) Ostfeld RS, Canham CD, Oggenfuss K, et al. Climate, deer, rodents, and acorns as determinants of variation in Lyme disease risk. PLoS Biol 2006 June; 4(6): e145. Published online 2006 May 9. doi: 10.1371/journal.pbio.0040145


(13)  Khasnis AA, Nettleman MD. Global warming and infectious disease. Arch. Med. Res.2005; 36: 689–96.


(14) Patz J, Daszak P, Tabor G, et al. Unhealthy landscapes: Policy recommendations on land use change and infectious disease emergence. Environ Health Perspect 2004; 112: 1092–1098.


(15) 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.


(16) Hofmeester TR, Jansen PA, Wijnen HJ, Coipan EC, Fonville M, Prins HHT, Sprong H, van Wieren SE. 2017 Cascading effects of predator activity on tick-borne disease risk. Proc. R. Soc. B 284: 20170453. http://dx.doi.org/10.1098/rspb.2017.0453


(17) Stafford KC III, Tick management handbook: an integrated guide for homeowners, pest control operators, and public health officials for the prevention of tick-associated disease.(PDF) New Haven, Connecticut: The Connecticut Agricultural Experiment Station 2007.


(18) Fox MW, Healing animals and the vision of one health CreateSpace publications and Amazon.com, 2011

 




Check the link below for a Dr. Fox C-Span feature concerning "Animal Testing"

Dr. Michael W. Fox on C-Span



--Video Link--

OUR ANIMAL RELATIONSHIPS: THE MOMENTS OF TRUTH PROJECT
Dr. Michael W. Fox

What right do we humans have to exploit other animals?  Where does that right come from and what are the limits if any?  What duties or obligations do we have in our relationships with our dogs, cats and other animals domesticated and wild?

          Follow and support Caroline Kraus and her Moments of Truth Project documentary film as she travels across the U.S. asking people, who variously live, work with and care for animals, these and other relevant questions.

Is there an overriding consensus and what are the reasons why people respond very differently to these questions, which in part examine our character, culture and future?

The viewing and discussion of this kind of documentary should be part of every school curriculum and will be of interest to all who work with, profit from and care for animals. Project Home Page: http://momentsoftruthproject.com/  To see the interview with Dr. Fox go to http://momentsoftruthproject.com/dr-michael-fox/