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 North America, with about 300,000 cases each year. Most cases occur in the northeastern and north central U.S., with relatively few in the south, even though the vector tick is present in all of these regions. The purpose of this research is to elucidate the ecological reasons for this geographical gradient in Lyme 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 in tick host-seeking behavior 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.

The Future: The distribution of Lyme disease in the coming decades will depend on the interactions between tick populations and local environmental conditions, especially in view of climate change. The insights gained from the geographical gradients study can be combined with predicted changes in climate and vertebrate distributions to predict changes in Lyme disease patterns, with implications for public health and disease management.