Deer and Lyme Disease, Research on the Relationship
This page presents a collection of the latest research on the deer-Lyme disease relationship. See the left bottom of the page for efforts to deliver safe pesticides to deer in order to reduce tick populations. Lyme disease is named for the rural Connecticut town where it was first found in 1975. Where foxes thrive, Lyme disease doesn't September 10, 2012 New York, Poughkeepsie Journal ... Taal Levi has studied environments from Brazil to Alaska ... His statistical analysis showed little correlation between the prevalence of deer and the incidence of Lyme. If that were the case, Levi said, “then why is Lyme disease so relatively rare in Western New York when deer are more abundant than in places here that have lots of Lyme disease?” ...Levi used statistical data to show that as fox populations went down, Lyme went up. The statistical connection between Lyme and other species wasn’t as consistent. The study was published in the Proceedings of the National Academy of Sciences in June... Have deer gotten a false rap for Lyme disease? August 3, 2012 Earthwise [includes pictures and podcast] ... While deer host lots of ticks, so do other vertebrates, including raccoons, skunks, and white-footed mice. Eliminate deer, and ticks will feed on other hosts. Also, while deer don’t transmit the Lyme bacterium to ticks—the smaller mammals do. Rick Ostfeld, a senior scientist at the Cary Institute of Ecosystem Studies, has written a book on Lyme disease ecology… East Hampton, Deer in Town Sights July 5, 2012 New York, East Hampton Star ... As for Lyme disease, the Group for Wildlife suggests that the town do more to educate the public about how to avoid tick bites and to prohibit the hunting of turkeys, which eat immature ticks. Because Lyme disease is also spread by ticks that feed on the white-footed mouse, the report says, “it’s unlikely that any reduction of deer populations can alleviate the disease.” ... if deer were eliminated, the ticks would feed on other animals ... two recent studies show that “four-poster” stations, where deer are exposed to tick-killing chemicals, reduced ticks by 69 to 100 percent.... Missing Foxes Fuel Lyme Disease Spread June 18, 2012 LiveScience.com Researchers used to think the increases were due to increasing deer populations ,,, However, the new data show these increases were independent of deer population levels... "Increases in Lyme disease in the Northeastern and Midwestern United States over the past three decades are frequently uncorrelated with deer abundance and instead coincide with a range-wide decline of a key small-mammal predator, the red fox, likely due to expansion of coyote populations,"... in the journal Proceedings of the National Academy of Sciences (June 18, 2012 article). Council Talks Deer Management, Chevy Chase Program Deemed A Success? February 28, 2013 Maryland, Bethesda Now ... County data shows the deer management program racked up 5,598 deer kills during the 2012-2013 seasons, 5,571 in 2011-2012, 5,969 in 2010-2011 and 5,599 in 2009-2010. Despite those totals... In the case of Lyme disease, which some dispute is related to deer overpopulation, the numbers have also remained steady. There were 297 confirmed and probably cases of Lyme disease in the county in 2011 and 296 in 2010, the two most recent years that those statistics were available. Surprise Culprits of Lyme Disease Boom June 18, 2012 Discovery News Deer are not to blame for rising rates of Lyme disease ... Foxes don’t spread Lyme disease directly. Instead, they cull populations of small mammals, which are responsible for the bulk of infectious ticks. Where foxes are thriving, the risk of disease drops. But when fox numbers fall – often because coyotes move in, small mammal populations surge and Lyme disease flourishes. Predators, Prey and Lyme Disease June 18, 2012 New York Times (blog) ... While people used to blame deer for the spread of Lyme disease, Dr. Levi said that scientific evidence has indicated that deer probably aren’t significant transmitters of B. burgdorferi bacteria because their systems tend to quickly flush it out. ... models showed higher numbers of Lyme disease cases in places where there are fewer foxes. They detected no significant relationship between numbers of deer and numbers of Lyme disease cases. Deer, predators, and the emergence of Lyme disease Proceedings of the National Academy of Science. June 18, 2012. Taal Levi, A. Marm Kilpatrick, Marc Mangel, and Christopher C. Wilmers Abstract Lyme disease is the most prevalent vector-borne disease in North America, and both the annual incidence and geographic range are increasing. The emergence of Lyme disease has been attributed to a century-long recovery of deer, an important reproductive host for adult ticks. However, a growing body of evidence suggests that Lyme disease risk may now be more dynamically linked to fluctuations in the abundance of small-mammal hosts that are thought to infect the majority of ticks. The continuing and rapid increase in Lyme disease over the past two decades, long after the recolonization of deer, suggests that other factors, including changes in the ecology of small-mammal hosts may be responsible for the continuing emergence of Lyme disease. We present a theoretical model that illustrates how reductions in small-mammal predators can sharply increase Lyme disease risk. We then show that increases in Lyme disease in the northeastern and midwestern United States over the past three decades are frequently uncorrelated with deer abundance and instead coincide with a range-wide decline of a key small-mammal predator, the red fox, likely due to expansion of coyote populations. Further, across four states we find poor spatial correlation between deer abundance and Lyme disease incidence, but coyote abundance and fox rarity effectively predict the spatial distribution of Lyme disease in New York. These results suggest that changes in predator communities may have cascading impacts that facilitate the emergence of zoonotic diseases, the vast majority of which rely on hosts that occupy low trophic levels. Climate, Deer, Rodents, and Acorns as Determinants of Variation in Lyme-Disease Risk Ostfeld RS, Canham CD, Oggenfuss K, Winchcombe RJ, Keesing F (2006) Climate, Deer, Rodents, and Acorns as Determinants of Variation in Lyme-Disease Risk. PLoS Biol 4(6): e145. doi:10.1371/journal.pbio.0040145 Indices of deer abundance had no predictive power, and precipitation in the current year and temperature in the prior year had only weak effects on entomological risk. The strongest predictors of a current year's risk 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. We conclude that interannual variation in entomological risk of exposure to Lyme disease is correlated positively with prior abundance of key hosts for the immature stages of the tick vector and with critical food resources for those hosts. Biodiversity and Disease Risk: The Case of Lyme Disease Richard S. Ostfeld and Felicia Keesing Conservation Biology Vol. 14, No. 3 (Jun., 2000), pp. 722-728 "A positive correlation between Lyme disease per capita and species richness of ground dwelling birds . . ." Full Abstract: Utilitarian arguments concerning the value of biodiversity often include the benefits of animals, plants, and microbes as sources of medicines and as laboratory models of disease. The concept that species diversity per se may influence risk of exposure to disease has not been well developed, however. We present a conceptual model of how high species richness and evenness in communities of terrestrial vertebrates may reduce risk of exposure to Lyme disease, a spirochetal (Borrelia burgdorferi) disease transmitted by ixodid tick vectors. Many ticks never become infected because some hosts are highly inefficient at transmitting spirochete infections to feeding ti cks. In North America, the most competent reservoir host for the Lyme disease agent is the white-footed mouse (Peromyscus leucopus), a species that is widespread and locally abundant. We suggest that increases in species diversity within host communities may dilute the power of white-footed mice to infect ticks by causing more ticks to feed on inefficient disease reservoirs. High species diversity therefore is expected to result in lower prevalence of infection in ticks and consequently in lower risk of human exposure to Lyme disease. Analyses of states and multistate regions along the east coast of the United States demonstrated significant negative correlations between species richness of terrestrial small mammals (orders Rodentia, Insectivora, and Lagomorpha), a key group of hosts for ticks, and per capita numbers of reported Lyme disease cases, which supports our "dilution effect" hypothesis. We contrasted these findings to what might be expected when vectors acquire disease agents efficiently from many hosts, in which case infection prevalence of ticks may increase with increasing diversity hosts. A positive correlation between per capita Lyme disease cases and species richness of ground-dwelling birds supported this hypothesis, which we call the "rescue effect." The reservoir competence of hosts within vertebrate communities and the degree of specialization by ticks on particular hosts will strongly influence the relationship between species diversity and the risk of exposure to the many vector-borne diseases that plague humans. Dilution Effect, "the scientific evidence as I’ve reviewed it, without any preconceived notion or political agenda or any other agenda, does not support the notion that tick numbers and Lyme disease risk are strongly correlated with deer numbers, and the data do not suggest that if you manage deer by hunting, you’ll reduce the number of Lyme cases.” Dr. Richard S. Ostfeld Disease Ecologist Ph.D., 1985, University of California. Buy the book on Amazon: Lyme Disease: The Ecology of a Complex System Acorns And Mice Driving Unusual Lyme Disease Risks (ICEID 2) March 14, 2012, Wired News Dr. Richard S. Ostfeld of the Cary Institute of Ecosystem Studies in Millbrook, New York, explained .. Mice also can survive in much smaller areas than the larger animals, chiefly deer, that are usually blamed for perpetuating Lyme, Ostfeld pointed out. In sampling of “forest fragments” sliced up by development in three northeastern states, his team has not found a parcel in which mice did not thrive. Larger parcels with more balanced ecosystems, with natural mouse predators and larger mammals, actually tend to have lower Lyme density ... White-tailed deer live throughout Minnesota, but blacklegged ticks are not found everywhere that deer live From Michigan Department of Natural Resources (Lyme disease): The relationship between deer and the disease is complex. Deer show no symptoms of the disease. Deer may carry small numbers of the spirochete that causes Lyme disease but they are dead-end hosts for the bacterium. Deer cannot infect another animal directly and no deer hunter has acquired the disease from dressing out a deer. Infected ticks that drop from deer present little risk to humans or other animals since the ticks are now at the end of their life cycle and will not feed again. There is no evidence that humans can become infected by eating venison from an infected deer. In addition, the Lyme organism is killed by the high temperatures that would be reached when venison is cooked or smoked. Deer supply the tick that transmits the bacterium with a place to mate and provides a blood meal for the female tick prior to production of eggs. Research has shown that white-tailed deer are important to the reproductive success of the black-legged tick. In the absence of deer, this tick will opportunistically feed on other medium sized mammals and humans. As a management tool for Lyme Disease, there is still debate in the scientific community as to whether reducing the number of deer present in an area will effectively or dramatically reduce Lyme Disease "risk". Research Summary: Deer are immune to Lyme disease and do not carry the diseases. If an infected tick bites a deer, the disease does not spread to other ticks that may bite the deer as it would if the tick bit a mouse. Reducing the number of deer may reduce the number of ticks, but because of the dilution effect, the result can be a higher percentage of remaining ticks with the disease since the ticks will choose other hosts that may be carriers of the disease. Deer also browse on the vegetation that provide tick habitat. While deer may provide a meal for the adult tick, research shows the risk of Lyme disease is statistically correlated to mice, chipmunks, and ground dwelling birds. Deer groom themselves, eliminating many ticks. Lyme disease originated in Connecticut Duke Forest, Our illogical war on deer February 9, 2013 North Carolina, The Durham News, Karin Yates ... According to John Rohm of the Virginia Department of Game and Inland Fisheries, “Reducing deer density by X will not = X percentage reduction in Lyme disease cases. ... Deer should not be blamed for the current Lyme disease situation. Integrated pest management would be more effective than focusing solely on deer.” Explanation for Chronic Lyme Disease Does this new study put an end to the chronic Lyme Disease controversy? Allentown Morning Call November 16, 2012 ... It's not one stubborn infection that is making them ill, states a study released this week by the New England Journal of Medicine, but multiple new infections. Researchers at the University of Pennsylvania and New York Medical College studied 17 patients, who had the classic erythema migrans rash associated with Lyme disease, more than once in a span of 20 years. They analyzed the genetic makeup of the Lyme-causing bacteria in those who had been sick several times. Each time, they were infected by different strains of the bacteria, ruling out relapses. Other Motives for the Lyme Disease Hunts Odgen Dunes, Deer Management Task Force Publishes Findings/Opinions July 12, 2012 Indiana, SaveOurDeer.Org ... Ogden Dunes has not come to a consensus on whether there is an overabundance of deer in Ogden Dunes. But they have come to a consensus that killing deer will not eliminate the risk of Lyme Disease ... Despite this development, the threat of a deer cull within Town limits seems to remain. Why? ... It appears the real reason for the deer cull was never to protect young families from the risk of Lyme Disease. The Town government was using the fear factor of Lyme Disease to promote the idea of a deer cull when the real reason was to kill deer to keep them from eating the plants of prominent town residents... | Information about the 4-poster System Used to Control Ticks on Deer Tick...Tick...Tick, white-footed mouse main reservoir for Lyme disease March 16, 2011 Rhode Island Patch.com Directed, produced, and narrated by Mary Healey Jamiel, "Hidden in the Leaves" is a 24-minute film about deer ticks. The DVD features the work of Thomas N. Mather, Ph.D., Director of the University of Rhode Island's Center for Vector-Borne Disease. ...
One study often cited as an example of reducing Lyme disease by reducing the deer population, was done on an offshore island with little biodiversity so few alternate hosts for ticks. Rand, P.W., et al. 2004. Abundance of Ixodes scapularis (acari:Ixodidae) after complete removal of deer from an isolated offshore island, endemic for Lyme disease. Journal of Medical Entomology 41:779-784 WILSON, M. L., DUCEY, A. M., LITWIN, T. S., GAVIN, T. A. and SPIELMAN, A. (1990), Microgeographic distribution of immature Ixodes dammini ticks correlated with that of deer. Medical and Veterinary Entomology, 4: 151–159. doi: 10.1111/j.1365-2915.1990.tb00273.x ABSTRACT. In order to determine whether the small-scale distribution of immature Ixodes dammini Spielman et al. corresponds closely to the activity patterns of white-tailed deer, Odocoileus virginianus (Zimmerman), these relationships were examined in a site on Long Island, New York, U.S.A. We first determined the extent and temporal pattern of adult ticks feeding on deer by examining twenty-three resident deer tranquilized during September-December 1985.1, dammini adults infested deer throughout this fall period, most abundantly during October and November. With radio-telemetry collars attached to deer we determined the relative frequency that they occupied 0.25 ha quadrats of the study site. During the following summer, we examined white-footed mice, Peromyscus leucopus (Rafmesque), that inhabited these quadrats and removed immature ticks from each. 8975 larval and 163 nymphal /. dammini were removed from 208 mice trapped in forty-three such quadrats. The frequency of deer using these quadrats was positively correlated with both the number of larval and of nymphal ticks per mouse. These results suggest that risk of I.dammini-borne zoonotic disease may be decreased by locally reducing deer density in sites that experience intense human activity. Localized Deer Absence Leads to Tick Amplification Localized Deer Absence Leads to Tick Amplification Sarah E. Perkins, Isabella M. Cattadori, Valentina Tagliapietra, Annapaola P. Rizzoli and Peter J. Hudson Ecology Vol. 87, No. 8 (Aug., 2006), pp. 1981-1986 Published by: Ecological Society of America Deer support high tick intensities, perpetuating tick populations, but they do not support tick-borne pathogen transmission, so are dilution hosts. We test the hypothesis that absence of deer (loss of a dilution host) will result in either an increase or a reduction in tick density, and that the outcome is scale dependent. We use a complementary methodological approach starting with meta-analysis, followed up by a field experiment. Meta-analysis indicated that larger deer exclosures reduce questing (host-seeking) tick density, but as the exclosure becomes smaller (<2.5 ha) the questing tick density is increased (amplified). To determine the consequences for tick-borne pathogen transmission we carried out a field experiment, comparing the intensity of ticks that fed on hosts competent for tick-borne pathogen transmission (rodents) in two small (<1 ha) deer exclosures and their replicated controls. Intensity of larval ticks on rodents was not significantly different between treatments, but nymph intensity, the tick stage responsible for tick-borne encephalitis (TBE) transmission, was higher in deer exclosures. TBE seropositive rodents were found in a deer exclosure but not in the controls. We propose that localized absence of deer (loss of a dilution host) increases tick feeding on rodents, leading to the potential for tick-borne disease hotspots. Deer-free areas may be haven for ticks, disease Penn State Study Reduced abundance of immature Ixodes dammini (Acari: Ixodidae) following incremental removal of deer. J Med Entomol. 1993 Jan;30(1):144-50 Deblinger RD, Wilson ML, Rimmer DW, Spielman A. Trustees of Reservations, Beverly, MA 01915. Abstract: The abundance of immature Ixodes dammini Spielman, Clifford, Piesman & Corwin was monitored for 9 yr (1983-1991) before and during the controlled, limited hunting of white-tailed deer, Odocoileus virginianus (Zimmerman), at a coastal Massachusetts site. Deer abundance was reduced from an estimated 350 during 1985 to approximately 60 during 1991. Although annual fluctuations were large, mean larval I. dammini abundance declined from 20.8 per white-footed mouse, Peromyscus leucopus (Rafinesque), during 1983-1986 before deer reduction to 10.3 per mouse following deer reduction (1987-1991). Similarly, mean nymphal I. dammini abundance declined from 2.7 per mouse before intervention to 1.6 per mouse after intervention. Immature I. dammini population fluctuations were not associated with those of P. leucopus. The total population of larvae infesting P. leucopus declined from 3,596 ticks before intervention to 1,535 ticks after intervention. Concurrently, the total nymphal population declined from 417 ticks before intervention to 187 ticks after intervention. The number of feeding adult female I. dammini on deer increased as deer density decreased. Freehold Township > Tick Borne Disease Ecology > Current Research Study Results. After three seasons, the estimated deer population was reduced by 46.7 %, from the 2002 post-fawning estimate of 2,899 deer (45.6 deer/km2) to a 2005 estimate of 1,540 deer (24.3 deer/km2). There was no apparent effect of the deer culling program on numbers of questing nymphal ticks in the culling areas and the overall numbers of host-seeking ticks in the culling areas appeared to increase in the second year of the program. The Lyme disease incidence rate generated by both passive and active surveillance systems showed no clear trend among years and did not appear to vary with declining deer density. Cayuga Heights, NY: Richard Ostfeld, PhD Senior Scientist, the Cary Institute of Ecosystem Studies Author of Lyme Disease: The Ecology of a Complex System(2010, Oxford Univ. Press) • DEIS incorrectly states that linear correlations exist between deer and ticks • No scientific data support the existence of a deer density threshold below which ticks decline to low numbers • Deer actually reduce the prevalence of Lyme infection in tick populations • Adult blacklegged ticks feed on at least 27 mammal species, not just deer • It’s misleading for DEIS to use Monehgan Island study to predict what will happen in Cayuga Heights. Read Statement Cayuga Heights, NY: Tamara Awerbuch, PhD ,Instructor, Department of Population and International Health, Harvard School of Public Health • Incorrect assumptions are made in DEIS about the relationship between deer and “deer ticks”, which have no basis in science • There is no linear correlation between killing deer and the tick population • White-footed mice, and not deer, are the carriers of the agent of Lyme disease • In Ipswich, MA, Lyme disease kept growing following deer-killing program • “there is NO scientific justification for a deer killing program in your community”. Read Statement POPULATION AND COMMUNITY ECOLOGY, Effects of Reduced Deer Density on the Abundance of Ixodes scapularis (Acari: Ixodidae) and Lyme Disease Incidence in a Northern New Jersey Endemic Area ROBERT A. JORDAN, TERRY L. SCHULZE, AND MARGARET B. JAHN Freehold Area Health Department, 1 Municipal Plaza, Freehold, NJ 07728 J. Med. Entomol. 44(5): 752Ð757 (2007) ABSTRACT We monitored the abundance of Ixodes scapularis Say (Acari: Ixodidae) and the Lyme disease incidence rate after the incremental removal of white-tailed deer, Odocoileus virginianus Zimmermann, within a suburban residential area to determine whether there was a measurable decrease in the abundance of ticks due to deer removal and whether the reduction in ticks resulted in a reduction in the incidence rate within the human population. After three seasons, the estimated deer population was reduced by 46.7%, from the 2002 postfawning estimate of 2,899 deer (45.6 deer per km2) to a 2005 estimate of 1,540 deer (24.3 deer per km2). There was no apparent effect of the deer culling program on numbers of questing I. scapularis subadults in the culling areas, and the overall numbers of host-seeking ticks in the culling areas seemed to increase in the second year of the program. The Lyme disease incidence rate generated by both passive and active surveillance systems showed no clear trend among years, and it did not seem to vary with declining deer density. Given the resources required to mount and maintain a community-based program of sufficient magnitude to effectively reduce vector tick density in ecologically open situations where there are fe impediments to deer movement, it may be that deer reduction, although serving other community goals, is unlikely to be a primary means of tick control by itself. However, in concert with other tick control interventions, such programs may provide one aspect of a successful community effort to reduce the abundance of vector ticks. Overpopulation problems December 20, 2010 Part 2 of 3 The Adirondack Daily Enterprise Biologists Felicia Keesing and Richard Ostfeld reject the tick-Lyme disease connection, noting that studies in New York and New Jersey found no correlation between the number of deer and the number of ticks in a region. These researchers argue that when deer are scarce, ticks simply move to alternate hosts: raccoons, skunks, opossums and other medium sized animals. Keesing and Ostfeld note that Lyme disease is rare in Southeastern and most Midwestern states, regions of the country where deer are plentiful.  Tick Management for Deer Deer and Elk Farmers DIscussion The dosage rate we use is 250ml of Ivomec (pour-on) per ton of feed. We prep the feed in the following manner. Using a small spray bottle, we mix 12 ml of ivomec to 2 pints of water. We then take 100# of feed and spread it out on a 4x8 sheet of untreated plywood. We spray a light coat( about 1/2 of the mixture) of the ivo/H20 mix over the feed, then allow to dry completely. If you use a feed with a water sheild on it, it less effective. Using a simple dust-pan, we scoop and flip the feed over, much like flipping a pancake on the griddle, then apply the remaining amount of the mixture to the other side of the feed and allow to dry completely. Replace it back into the bags and distribute it just like you are using normal feed. It is important to do this on a warm sunny day when possible, and always wear latex gloves. In our bulk trough feeders, we coat the top of the feed with the same dosage rate per pound, and allow the deer to eat through the layer of ivomec. We do this every6 months, alternating with Purina Exotic Animal De wormer on a 6 month rotation, providing a worming treatment every quarter. We try to time it as to not have any of the treatments closer than one month to the birthing of fawns. This is easy if you have a single species in the enclosure, but in multiple species populations, it requires a good deal of thought to maximize the gaps between birthing cycles. Having said that, we have had births in some of the horned species within days following a treatment with no adverse affects. This works well in helping control ticks. In addition to these treatments, we use powdered garlic in our feed at the rate of 2# per ton of feed throughout the year. I find it to be very effective in reducing ticks and the animals do not seem to mind the taste. Some Contradictory Results from Connecticut The use of deer vehicle accidents as a proxy for measuring the degree of interaction between human and deer populations and its correlation with the incidence rate of Lyme disease. DH Wiznia, PJ Christos, AM LaBonte - Journal of environmental health, 2013 ... The authors also examined the relationship between deer population density and human Lyme incidence rate. They analyzed data from Connecticut's Department of Environmental Protection and the Department of Public Health from 1999 through 2008 by deer management zone (DMZ) and town. For DVA incidence rate versus Lyme incidence rate for both DMZs and towns, most of the correlation coefficients computed yearly were moderate to strong and all of the p-values were significant. A weak correlation was observed between deer population density and Lyme disease incidence rate by DMZ. The authors propose DVAs as a proxy for measuring the interaction between coexisting populations of humans and deer. |