Wildlife and Human Health

Deer Hunting and Lyme Disease

The MSPCA recognizes the widespread concern regarding Lyme disease and the need for more information and education on the issue. The pervasive but incorrect common name, "deer tick", suggests a correlation between deer and tick-borne Lyme disease and has caused communities to increase deer hunting in a futile attempt to reduce the threat of Lyme disease.  In fact, there was no correlation between deer and ticks found in recent studies (e.g., Jordan and Schulze, 2005; Ostfeld et al., 2006; Jordan et al., 2007)  [i]  Ticks do not require a specific host and can thrive by feeding on white footed mice and other small animals so, when deer numbers are reduced, ticks will find other, more efficient hosts (better able to transmit a bacterial infection to feeding ticks), which can actually increase the risk of humans contracting Lyme disease.   In order to effectively reduce the number of Lyme disease cases, the number of disease carrying ticks needs to be reduced, not the number of deer.  Read a recent article on the deer-Lyme disconnect and the new book, "Lyme Disease - The Ecology of a Complex System" by Rick Ostfeld.
  

Black legged ticks have a two-year life complex cycle with three stages: larvae, nymph and adult, during which they can use various host species, therefore tick abundance and distribution is affected by many factors. According to the American Lyme Disease Foundation, due to its small size, an infected nymph tick can go unnoticed until they are fully engorged and are “therefore responsible for nearly all of  human Lyme disease cases.”[ii]  Ticks have to feed on an infected vertebrate host to get and transmit Lyme disease: these hosts, also called wildlife reservoirs, vary in their effectiveness for transmitting Lyme – deer are highly ineffective, whereas mice and other rodents are much more effective.  If tick-borne diseases are to be successfully addressed, efforts need to focus on decreasing the number of ticks throughout their life cycle, not the number of hosts. 

Recommendations

The following tactics may be effective in reducing the number of tick-borne diseases:

1. Increase public education    

Since ticks in the nymph stage have a greater potential for infecting people, communities should focus on increasing the means by which they educate people about ticks, how to reduce the chance of getting one, and what to do when people are bitten. The Massachusetts Department of Public Health recommends that people protect themselves from ticks by using repellents, staying out of tall grassy areas, and checking for ticks every day.

According to Assistant State Epidemiologist at Maine’s Department of Health and Human Services, education is the key to prevention because “a deer tick [sic] will not transmit Lyme disease if removed within 24 to 36 hours”[iii]

2. Install deer treatment bait stations and bait boxes for mice and other small mammals

Treating deer with products that kill ticks should be more effective than killing deer because ticks will seek alternate hosts if deer are missing and those alternate hosts will be more effective at transmitting disease. Deer treatment bait stations ("4-poster devices") can be installed; in some locations this may require permission from the state wildlife agency (read a recent article about research in MA). The American Lyme Disease Foundation, Inc. recommends a relatively inexpensive deer treatment bait station; deer using the feeding station are forced to rub up against applicators that apply a pesticide to their ears, heads, necks and shoulders where approximately 90% of feeding adult ticks are attached.[iv]

 “Bait boxes” for mice and other small mammals (chipmunks, shrews) use fipronil, also used in Frontline spot treatments for cats and dogs; this approach has been shown to reduce tick burdens on mice and abundance of questing nymph ticks – and, even more importantly -a reduction in tick infection with B.burgdorferi

3. Modify habitat to reduce the number of ticks in high-use areas

Increased diversity (decreased forest fragmentation) protects from exposure to Lyme disease, so habitats should be kept in-tact as much as possible.  Habitat modification and pesticides can be used to reduce the number of ticks in recreational areas. Places with “low-lying vegetation, shrubs and grasses surrounding campgrounds or backyards should be close cropped or mowed to discourage tick movement and nesting. An approved residual insecticide should then be broadcast into the surrounding vegetation to establish an effective chemical barrier. A similar process, but on a smaller scale, can be followed for well-defined hiking trails.  Control should be aimed at the nymphal stage, which is the most likely stage to transmit the disease to humans. One application of a pesticide should be made at nymphal population peak. A second application toward the end of the nymphal stage, in late July to early August, is also suggested.”[v]

The MSPCA’s Living With Wildlife philosophy involves effective strategies that are long lasting; reducing deer herds will not successfully address the tick-borne disease. We agree with the many professionals who recognize that this issue needs to be addressed through education, prevention, and innovative pesticide methods that directly affect the ticks.  Download a factsheet on Lyme disease.

For more information on Lyme disease, please visit the following:

Cary Institute of Ecosytem Studies

American Lyme Disease Foundation

Massachusetts Department of Public Health

Center for Disease Control


Endnotes

[i] Jordan RA and TL Schulze. 2005. Deer browsing and the distribution of Ixodes scapularis (Acari: Ixodidae) in central New Jersey forests. Environmental Entomology 34: 801-806.
Jordan, RA, TL Schulze, and MB Jahn. 2007. Effects of reduced deer density on the abundance of Ixodes scapularis (Acari: Ixodidae) and Lyme disease incidence in a northern New Jersey endemic area. Journal of Medical Entomology 44: 752-757.
Ostfeld RS, CD Canham, K Oggenfuss, RJ Winchcombe, F Keesing. 2006. Climate, deer, rodents, and acorns as determinants of variation in Lyme-disease risk. PLoS Biology 4: 1058-1068.

[ii] American Lyme Disease Foundation, “Deer Tick Ecology”.  http://aldf.com/deerTickEcology.shtml  

[iii] Beckett, Geoff (Assistant State Epidemiologist Maine Department of Health and Human Services). “Toxic tick bites: Incidents increase in Midcoast”, Village Soup. November 9, 2004.

[iv] American Lyme Disease Foundation, “The ‘4-Poster’ Deer Treatment Bait Station http://aldf.com/fourPoster2.shtml

[v] Caron, Dewey. “Tick Control” University of Delaware, Cooperative Extension Entomologist. 1996  http://ag.udel.edu/extension/information/hyg/hyg-13.htm