Environmental risk and prevention of Lyme disease.

An understanding of the environmental determinants of Lyme disease risk is essential to evaluate human disease potential and to recommend strategies for disease prevention. Tick vectors of Lyme disease require a vertebrate blood meal during each of three motile developmental stages (larva, nymph, and adult). Although the immature stages (larvae and nymphs) exhibit broad and overlapping host ranges, adult ticks are primarily dependent on deer for feeding and reproduction. Consequently, the distribution and abundance of these ticks often reflect those of deer. Several species of smaller mammals and some birds that host immature ticks are also competent reservoirs for Borrelia burgdorferi, which becomes established within the tick population during feeding. The relative abundance of these host species and their ability to infect ticks are key factors in determining the distribution of Lyme disease risk in the local environment. Available methods for reducing the risk of Lyme disease in the environment include the application of insecticides and use of deer fencing, which have been shown to be 83-97% effective in reducing risk. However, the adverse environmental impact of insecticides and high cost of deer fencing limit these methods to high-risk areas where human exposure is constant and unavoidable (i.e., residential or occupational). Personal protection in high-risk areas can lessen the likelihood of contact with ticks. Future prevention methods may include host-targeted insecticides, environmental alteration, and biologic control. Moreover, research is currently directed to identifying antigens for use in recombinant human vaccines.