Vector-borne Disease Research

Science Center Objects

Lyme disease is the most prevalent vector-borne disease in North America, with about 300,000 cases per year in the U.S.  We are studying transmission of the spirochete that causes this disease among wild animals and the blacklegged tick vectors, to determine why Lyme disease is common in the northeast and northern Midwest but rare in the south, even though blacklegged ticks are present in all of these regions.  Our research suggests that tick genetics, behavior, host associations, and climate all contribute to this geographical gradient in human disease. 

The Challenge: Lyme disease, which is caused by a tick-transmitted spirochete, is the most common vector-borne disease in the United States, with an estimated 300,000 cases each year. Human cases of Lyme disease are common in the northern U.S., but rare in the south, even though the tick vector is present in both regions. West Nile Virus (WNV) is the most common mosquito-transmitted pathogen, with thousands of cases yearly. The purpose of this research is to elucidate the natural transmission dynamics of these pathogens, so that we can understand the natural transmission dynamics of these pathogens, better predict human exposure, and design well-targeted, efficient methods to prevent human disease.

The Science: The north-south differences in Lyme disease incidence could result from differences in climate, tick-host associations, or genetic differences between geographically separate tick populations. A team of researchers from several universities, Patuxent, and the Public Health Agency of Canada have sampled ticks, hosts, and climatic data from sites in the eastern and central U.S., and have found that all of these factors contribute. In particular, north-south genetic differences result in geographical differences in tick host-seeking behavior that explain much of the observed distribution of Lyme disease.  Laboratory experiments suggest that this difference in behavior results, at least in part, from differences in climate between the northern and southern regions. Geographical trends in tick-host associations also appear to be important.

The Future: Geographical trends in tick-host associations, and their effects on natural transmission cycles of the Lyme spirochete, are currently being analyzed. We are also assessing possible effects of climate change on Lyme transmission. Recent results suggest that infection with the Lyme spirochete affects tick survival, and possibly behavior.  Studies are planned to determine whether effects of infection on tick life histories influence spirochete fitness. Analyses of transmission patterns of another tick-transmitted spirochete, Borrelia miyamotoi, are in progress.