Ending the Lyme disease epidemic: a real possibility
The following information is provided by the CT Dept of Public Health and the CT Agriculture Experiment Station's National Tick Experts:
- Lyme incidence parallels deer population growth
- Fairfield County has the highest number of cases of Lyme disease in Connecticut
- Connecticut has the highest rate of Lyme in the United States
- Reducing deer numbers reduces tick numbers
- Reducing deer to below 8 to 10 per sq mile breaks the tick life cycle and prevents Lyme disease
A community in Maine decided in the 1990s to try and rid itself of Lyme disease. And after only 5 years they have achieved just that. Monhegan residents were suffering from a high rate of Lyme disease when they voted to take action. After failing to achieve their goal through the use of chemicals that attack deer ticks the residents voted to remove all the deer from their island.
Monhegan Island, 10 miles off the coast of Maine had no native deer until 1955 when they were intentionally introduced at the request of islanders. By the late 1980’s deer ticks were becoming abundant and by the mid 1990’s the deer population had reached an incredible 100 per sq mile. By 1996 13% of residents had Lyme disease. Recognizing the source of the problem, the residents voted to remove every deer from the island. Remarkably, within 5 years of this being completed, the number of new cases of Lyme disease had fallen to zero.
Lyme disease was first recognized in a group of arthritis patients from the area of Lyme, CT in 1975. The number of new cases of Lyme disease has since grown dramatically. Nationally, 7,900 human cases were reported in 1990 and 23,763 cases were reported in 2002. Connecticut has the highest incidence of Lyme of all the 50 states. Fairfield County has the highest number of cases of any county in the US. The true number of cases is estimated by the US Center for Disease Control (CDC) to be 10 fold higher as many cases go unreported. There were an estimated 360 new cases in Easton (population 7,000) in 2002, and 950 in Ridgefield compared to just 70 in all of Hartford (population 120,000).
Easton resident Tony Neidenbach, who moved back to the US after 3 years in England, was horrified when he realized that he had settled his family in the epicenter of the biggest Lyme epidemic in the world. He had his first experience with deer ticks and Lyme disease only 3 months after moving in when he found an embedded tick on his leg. It took some Internet research by his wife and several trips to his doctor before he realized the cause of his rash and exhaustion. He remains surprised at the complacency and resignation of other residents to the risks.
Despite prevention efforts, Lyme disease continues to increase. The public health response to the growing Lyme epidemic has focused on protective measures to reduce personal exposure to the deer ticks that transmit the disease to humans. Thorough daily body checks for ticks, the wearing of protective clothing when outdoors and using tick repellants can be effective for individuals. Surveys show that many homeowners follow these recommendations as well as undertaking landscape modifications such as creating a woodchip or gravel barrier around yards. However, these measures have failed to curb the rapid increase in the rate of Lyme disease.
Relationship between Deer and Lyme
There is a close relationship between the rising numbers of Lyme cases and the proliferation of deer across the United States. Areas with high rates of Lyme correspond with areas of the US that are highly populated with deer: the Northeast, upper Midwest and the west coast. Lyme disease bacteria are carried by the black-legged or deer tick. The white-tailed deer is the essential large mammal host in the successful completion of the complex 2-year life cycle of the deer tick. Even though adult ticks can feed on other mammals such as dogs, cats and raccoons, the female adult tick requires a blood meal from the deer before she can lay her 2,000 to 6,000 eggs. These eggs hatch into immature ticks that transmit the Lyme bacteria to small mammals such as white-footed mice and chipmunks and to many birds. Deer, however, play a unique role in the completion of the tick life cycle and provide a real opportunity to effectively control Lyme disease by reducing the numbers of just one species below the threshold for successful tick reproduction.
In landmark studies performed almost 20 years ago by researchers at the Connecticut Agricultural Experiment Station on a group of 6 islands in Narragansett Bay, Rhode Island, it was found that on the 2 islands with deer and mice, Lyme bacteria were detected in mice and meadow voles (Anderson). Neither Lyme bacteria nor ticks were found among the small mammals on the four islands that had no deer. This raised the question of whether a reduction in a deer population could reduce tick numbers sufficiently to prevent human infection. Other studies showed that frequent sighting of deer in backyards and living in proximity to a wildlife conservation area are associated with a greater incidence of human Lyme infection (Lastavica). Furthermore when deer numbers were reduced Lyme case numbers fell. Similar results were found in Great Island, Massachussetts (a peninsula, not an island) where Lyme and babesia cases have been kept very low for 20 years now with 6 deer per sq mile (Telford, Wilson). Scientists concluded that Lyme disease does not have to be a fact of life. It is a direct consequence of the increasing abundance of deer, as documented in numerous studies on the effects of deer reduction. These studies are now becoming available with startling results.
Could reducing deer numbers in Connecticut prevent Lyme disease?
Dr Kirby Stafford, PhD., an expert on ticks with the CT Agriculture Experiment Station (caes), thinks it could: “Deer are the key to tick abundance. If we could bring deer ticks low enough we could break the cycle between reservoir hosts and ticks. No ticks, no Lyme disease.” The study by Dr Peter Rand of the Maine Medical Center confirmed that this approach worked on Monhegan Island, Maine. Other studies have shown that it is not necessary to completely eliminate deer: reducing the deer population to 8 per square mile or less is sufficient to prevent most if not all ticks from reproducing and will dramatically reduce the rate of Lyme disease.
The Mumford Cove deer management program “has resulted in a reduction in the local tick population as well as a reduction in the risk of contracting Lyme disease by residents,” said deer biologist Howard Kilpatrick of the Department of Environmental Protection deer management program. An eight year follow up of this dramatically lowered Lyme incidence is being prepared for publication.
How can deer numbers be reduced?
Because urban deer have small home ranges, hunters can produce localized reductions in deer populations even if all the surrounding towns do not take part in a program. However, in the last 5 years many local Fairfield County towns have acknowledged the multiple problems caused by excess deer numbers and instituted deer reduction programs through controlled, planned hunting.
The Town of New Canaan after a costly public opinion survey in 2000 and aerial assessment of the deer population in Feb 2001, which revealed densities of over 40 deer per square mile, and around 45% of all households affected by Lyme, encouraged residents to permit licensed bow hunters to hunt deer. Ninety-five percent of New Canaan’s land is under private ownership. Wilton has now run two annual controlled hunts. Weston has begun reducing its deer numbers from 65 per sq mile through private hunting and the annual controlled hunt at Devil’s Den, a Nature Conservancy property shared with Redding, and is aiming for 10 per square mile. The Town of Greenwich and Audubon Greenwich have realized the severity of their deer problem and are both using controlled hunts in limited areas to reduce deer numbers, but without much hope yet of making a dent in overall deer numbers in Greenwich.
Many towns struggle to make an overall impact on the deer population due to the short regulated hunting season, the limitation to archery in many situations and the reluctance of residents to accept the need due to poor and misinformation on the role of deer.
What more could be done to help reduce deer numbers?
The most important thing to understand is that CT DEP sets deer population levels through their regulations and this is the state agency to appeal to for help in getting town deer numbers back under control. They have special permit programs available for controlling deer in problem residential areas that allows deer removals (by professionals or trained volunteers) outside the sport hunting season and with different techniques. It has also been suggested that extending the recreational hunting season by another month or two would be very effective. Dr Sam Telford of Harvard University, pointed out that “expanding hunting is free, effective and safe. In addition it contributes to the local economy.” Leadership and directives from bodies such as the Dept of Public Health and from the DEP would go a long way toward facilitating effective deer control, much of which relies on private land owners allowing hunters onto their land. Individual towns may differ in how they accomplish deer control, due to differences in development and land ownership and in local statutes. But all towns would benefit from a public information campaign and statement of intent from the national or State level.
Is there public support for deer reduction?
Just recently several Lyme advocacy groups have spoken out in support of deer management to reduce Lyme disease: Lyme Disease Foundation director Thomas Forschner said in an interview on March 28, “There is definitely a relationship between the number of deer and the number of Lyme cases. If we could control the deer we could control the incidence of Lyme disease.” He added, “I don’t care what it takes, I want to end this disease.”
American Lyme Disease Foundation director David Weld said in an interview, also in March, “We strongly support efforts to significantly reduce the deer population, which in turn will help eliminate Lyme disease and other tick-borne diseases.”
Dr Draper, Health Director and Medical advisor to the City of Danbury and co-chief of the Task Force on Lyme Disease at Danbury Hospital strongly favors prevention of Lyme disease through deer management. He has conducted exit surveys at recent Lyme conferences and found around 90% support amongst health workers for “community efforts to reduce the deer population.”
It is possible to reduce the number of new cases of Lyme disease through effective deer population reduction but will people choose to make this decision? With the knowledge that deer numbers in Connecticut must be returned to less than 12 per square mile to save the woodlands, will people choose to go one step further and reduce deer numbers to 8 per square mile? The rewards would be enormous. With the cooperative engagement of public health officials, clinicians, and residents of the affected communities it may be possible to reduce the rate of Lyme significantly or perhaps even eradicate Lyme disease. The first step is to inform people that this is an option. Due to the complexity of the spread of Lyme disease to humans this will have to begin with a public education campaign. The Cornell University publication “Community-based deer management” summarizes the experience of several communities, including Monhegan Island, Maine and other examples from New Jersey, Virginia, New York and Connecticut that successfully implemented deer population management and concludes that “as daunting as deer management can sometimes seem, success often is possible.”
Now three years later, Mr. Neidenbach of Easton has joined the Fairfield County Deer Management Alliance (FCDMA), a group formed just over a year ago to promote deer population reduction. He is one of thirteen municipal representatives making an effort to inform the public about the alternative to living with ticks, deer and Lyme disease and to create some momentum for change. He hopes to gain back some of the freedom to enjoy the outdoors with his kids that he felt in England.
Source material on deer reduction studies:
Connecticut Department of Public Health and Dr Kirby Stafford: Tick Management Handbook 2004: CT community based Lyme disease prevention projects. Funded by Centers for Disease Control and Prevention and by the Connecticut Agriculture Experiment Station. Available at www.caes.state.ct.us
Sam Telford 2002 Conservation Medicine: Aguirre, Ostfeld eds: Ecological Health in Practice, pp310-324; Oxford University Press. Deer reduction studies on Great Island, Cape Cod, MA and effects on Lyme incidence.
Anderson, JF, Johnson, Magnarelli et al 1987. Prevalence of Borrelia burdorferi and Babesia microti in mice on islands inhabited by white-tailed deer. Appl Env Microbiol 53:892-894
Awerbuch and Spielman (Harvard School of Public health) study that showed that 8 per square mile was the critical number of deer:
http://www.fao.org/wairdocs/ilri/x5441e/x5441e05.htm#host density and tick dynamics: the case of the vector of lyme disease
Daniels TJ, Fish D and Schwartz I 1993. Reduced abundance of Ixodes scapularis and Lyme disease risk by deer exclusion. J Med Entomology 30: 1043-1049
Telford SR 1993. Forum: Deer tick transmitted zoonoses in the eastern United States. In Ginsberg ed. Ecology and Environmental Management of Lyme Disease. pp 310-324 Rutgers University Press.
Telford SR 1993. Forum: perspectives on the environmental management…In Ginsberg ed. Ecology and Environmental Management of Lyme Disease. pp164-167 Rutgers University Press
Wilson ML, Telford SR lll 1988. Reduced abundance of immature Ixodes dammini ticks following elimination of deer. J Med Entomology 1988;25:224-8
Wilson and Deblinger. Vector management to reduce to reduce the risk of Lyme disease. In Ginsberg ed. Ecology and Environmental Management of Lyme Disease. pp126-156 Rutgers University Press
Hayes EB and Piesman J 2003. How Can We Prevent Lyme Disease? New England J Med. 348;24 2424-2430
Piesman et al 1979. J Med Entomology 15:537-540 Role of deer in the epizootology…
Lastavica, C. C., M. L. Wilson, V. P. Barardi, A. Spielman, and R. D. Deblinger. 1989. Rapid emergence of a focal epidemic of Lyme Disease in coastal Massachusetts. New England Journal of Medicine 320: 133-137.
Peter Rand, Charles Lubelczyk and Robert Smith. 2003 Deer Density and the Abundance of Ixodes scapularis ticks. Journal of Medical Entomology Vol 40 pp179-184 Lyme Disease Research Laboratory, Maine Medical Center Research Institute.
Peter Rand and Robert Smith. 2004 Monhegan Island study. Journal of Medical Entomology Vol 41 pp779-784 Maine Medical Center Research Institute, Vector-Borne Disease Laboratory
Kirby Stafford CT Agriculture Experiment Station, New Haven Frontiers of Plant Science: Special Issue Vol 53 Number 2 Spring 2001: An Increasing Deer Population is Linked to the Rising Incidence of Lyme Disease.
Tick Management Handbook 2004 and 2007: CT community based Lyme disease prevention projects. Funded by CDC and Prevention and CT Agriculture Experiment Station.
Kilpatrick and LaBonte. 2003, Wildl. Soc. Bull: 31:340-348 Deer Hunting in a Residential Community (Mumford Cove)
Managing Urban Deer in Connecticut: A guide for residents and communities concerned about overabundant deer populations. Ct Dept of Env Protection. Howard Kilpatrick and Andrew LaBonte 2007 http://www.ct.gov/dep/lib/dep/wildlife/pdf_files/game/urbandeer07.pdf
Community-based deer management: 2004 Decker, Raik, Siemer. Cornell University Outreach Cooperative, NY. For sale online: cornell.edu