Passive and Aggressive Means of Deer Control

Evaluation of deer-targeted interventions on Lyme disease incidence in Connecticut.

Garnett JM, Connally NP, Stafford KC 3rd, Cartter ML.  Public Health Rep. 2011 May-Jun;126(3):446-54.

Reducing the number of blacklegged ticks (Ixodes scapularis), the vector for LD should in theory reduce the incidence of LD in an endemic area.  One such strategy targets white-tailed deer. 

Although deer are not competent reservoir hosts for the LD causative agent, Borrelia burgdorferi, they are the primary hosts for adult blacklegged ticks and are an important tick transport mechanism.  One study showed that more than 95% of adult female ticks feed on white-tailed deer.  Nymphal ticks will also feed on deer.  Therefore, deer-targeted interventions could provide a large-scale method for controlling tick populations by reducing the number and movement of blacklegged ticks.

Two proposed deer-targeted interventions have included a topical acaricide applied using a four-poster device and deer-reduction programs.  However, few studies have evaluated whether deer-targeted interventions resulted in decreased LD incidence, particularly in non-island settings.  The four-poster device is a passive topical treatment system developed by the U.S. Department of Agriculture, Agricultural Research Services.  A central bin stores and dispenses bait to attract deer.  As the deer feeds, rollers apply an acaricide directly to the head, ears, and neck, which is transferred to other body areas by self-grooming.  Studies of this device have shown a significant decrease in blacklegged tick abundance on deer and in the surrounding area.

Another deer-targeted intervention aims to reduce deer populations through a controlled deer hunt.  Two studies showed that complete, or near complete, elimination of deer was effective in reducing tick populations on an inhabited peninsula and islands off the northeastern U.S. coast.  However, it is unclear whether deer-reduction strategies will translate to mainland settings where deer cannot be eliminated completely. 

Four-poster:  The results of the four-poster analysis showed a general decreasing trend in EM rash incidence in all areas.  In the original treatment area, the mean incidence before treatment was 427.5 cases per 100,000; after treatment, the mean incidence was 137.8 cases per 100,000.

Deer hunt: The deer hunt analysis did not show a clear decreasing trend in EM rash incidence in the original treatment area.  In the original treatment area, the mean incidence rate before treatment was 450.8 cases per 100,000; after treatment, the mean incidence rate was 245.9 cases per 100,000.  The mean incidence rate was not significantly different before and after treatment.

CONCLUSIONS

Our findings suggest that the four-poster device was effective in decreasing the incidence of EM rash in an endemic area.  Despite a decrease in EM rash incidence,

however, we did not find a statistically significant effect of the deer hunt on EM rash incidence, probably due to LD reporting issues, study design limitations, and the small population size.  Further study is necessary to conclusively evaluate the effect of deer-targeted tick control interventions on LD incidence.  A prospective, multiyear study designed with consistent surveillance methods, a large population, and established control areas could provide reliable data for analyzing the effectiveness of deer-targeted interventions.  A combination of deer-targeted and other interventions, such as education, may ultimately prove to be successful in preventing LD in endemic areas.