Analyzing 30 years of data detailing a large rabies virus outbreak among North American raccoons, researchers at Emory University have revealed how initial demographic, ecological and genetic processes simultaneously shaped the virus's geographic spread over time. The study appears online in the Proceedings of The National Academy of Sciences.
"Our study demonstrates the combined evolutionary and population dynamic processes characterizing the spread of a pathogen after its introduction into a susceptible host population," says Leslie Real, PhD, Emory University Asa G. Candler professor of biology. During invasion, emerging pathogens, such as rabies, ebola and hantavirus, undergo rapid evolution while expanding their numbers and geographic range; yet, it is difficult to demonstrate how these processes interact, says Dr. Real.
However, this particular outbreak, which went largely unchecked until relatively recently, was unusually well documented both spatially and temporally. Data were methodically collected and stored since the outbreak began in the mid-1970s. In addition, the Centers for Disease Control and Prevention (CDC) had been stockpiling viral samples from the outbreak since 1982, giving scientists a treasure trove of genetic data ripe for analysis.
"Together these data offer a rare chance to examine how the demographic and spatial processes of spread and population expansion over 30 years have shaped viral evolution on a geographic scale," says Dr. Real. "Landscape features, such as rivers and mountains, can have a pronounced effect on the rate of rabies' spread and may therefore affect viral dynamics on a large scale," he says.
The study, for example, showed that because mountain ranges make for a poor raccoon habitat especially at higher elevations, raccoons did not cross the Appalachian mountain chain during the first part of the outbreak, which clearly limited the virus's westward expansion, says Dr. Real.
Contact: Holly Korschun