As has now been obvious for too long, we have a serious problem with tick-borne diseases on eastern Long Island. These can be challenging to diagnose and treat and sometimes progress to debilitating chronic or even fatal illnesses. More effective methods to control our excessive tick populations and prevent human infections are sorely needed.
As recently reported by Carrie Miller in your newspaper, a task force of the New York State Senate majority has proposed a multifaceted action plan for dealing with this public health crisis. Although this plan contains some useful suggestions for further studies and education, it is deficient in its recommendations for preventive measures that might work in the short term. Suggested measures focus only upon the possible wider deployment of “four poster” feeding stations to de-tick deer, a more thorough evaluation of chemical agents for reducing tick numbers around homes and studies of oral bait vaccines to eliminate tick-borne disease organisms from their natural, reservoir hosts.
Four posters work by applying a tickicide (permethrin) to deer when they feed on corn dispensed by the devices. This is important because deer provide a bountiful supply of blood for deer and lone star ticks at their adult, reproductive stage. Expansion of our deer population in recent years has contributed directly to explosions in the tick population and tick-borne diseases in humans. Although the deployment of four posters on Shelter Island is often cited as a success story, it has hardly been that. These devices are expensive to deploy, this must be done indefinitely and they must reach 90 percent or more of the deer to be adequately effective in reducing the overall tick population. The latter is a challenge for two reasons: Dominant deer in the population will drive less dominant animals from the feeders, thereby limiting or precluding tickicide treatment; and New York State regulations prohibit the placement of four posters within 300 feet of roads or where children might be present (unless the devices are fenced in). In many areas with severe deer problems, this would limit the placement of four posters at the recommended density of one device per 40 to 50 acres. The widespread deployment of four posters may also discourage deer hunting that’s desperately needed for environmental and agricultural reasons, because of a fear of pesticide contamination of the venison. Finally, the abundant food offered by four posters is problematic because it attracts other wildlife and could increase the spread of other serious zoonotic diseases. These would include rabies, leptospirosis and raccoon roundworm by raccoons, as well as hantavirus by deer mice. In some locations, four posters will probably promote rat problems as well.
Some people have understandably opted to treat their properties with acaricides during the tick season. It must be recognized that many of these will also kill highly beneficial insects (such as bees), fish and aquatic invertebrates.
While progress is being made to develop new vaccines directed against ticks or tick-borne diseases, this research is unlikely to provide a completely satisfactory solution anytime soon. Injectable vaccines for humans are likely to be limited to only one or two diseases, while we face the risk of contracting many (e.g., Lyme borreliosis and the related Borrelia miyamotoi, babesiosis, ehrlichiosis, anaplasmosis, Rocky Mountain spotted fever and a couple of newly emerging tick-borne diseases). Some oral bait vaccines suffer from the same deficiency, and all animal reservoir hosts for the diseases may not readily accept the baits. Other oral bait vaccines are intended to prevent tick feeding rather than to immunize hosts against disease organisms. Although conceptually appealing, this strategy is still at the research stage.
While all these approaches have shortcomings or are early in their development, it is now clear that one effective method of reducing tick levels and human cases of Lyme disease is already available. That is to substantially reduce excessive deer populations. In an important multiyear study just published in the Journal of Medical Entomology (Vol 51: 777-784, 2014), H.J. Kilpatrick and collaborators established that reduction of the deer density in the Mumford Cove community in Groton, Conn., to about 13.2 deer per square mile resulted in a 76 percent reduction in tick abundance and an 80 percent reduction in resident-reported cases of Lyme disease. As noted by these investigators and others, with insufficient deer available, tick populations cannot be sustained or are sustained at much lower levels.
On eastern Long Island, substantial reduction of our deer population can be achieved only by some combination of recreational hunting and humane culling. Fertility control is not affordable, truly feasible or approved as a stand-alone deer management method by the New York State Department of Environmental Conservation. Furthermore, this approach would do nothing to reduce tick abundance or other serious deer-related problems within any reasonable time period.
Dr. John Rasweiler, of Cutchogue, is a retired medical school professor and Cornell-trained reproductive physiologist who has spent much of his scientific career working with wildlife. He serves on the Town of Southold deer management committee, the Suffolk County Tick Control Advisory Committee and the board of the North Fork Deer Management Alliance.