Vaccinating wildlife can reduce human risk for Lyme disease

Durland Fish, Yale University Click here for a high resolution photograph.

Direct field evidence shows that Lyme disease in humans can be prevented by vaccinating wildlife, researchers in the Department of Epidemiology and Public Health at Yale School of Medicine report in the Proceedings of the National Academy of Sciences.

In a four-year study of isolated woodlands near New Haven, nearly 1,000 white-footed mice were trapped and either vaccinated against Lyme disease or given a placebo. Fewer deer ticks tested positive for Lyme disease in the experimental plots where mice had been vaccinated. Fewer ticks carrying infection reduced the risk for humans getting Lyme disease from a tick bite.

"Vaccinating wildlife increases our prevention options," said principal investigator Durland Fish, professor of epidemiology at Yale, who led the study with Jean Tsao, now at Michigan State University and microbiologist Alan Barbour at University of California at Irvine. "Despite a record increase in cases, efforts to prevent Lyme disease with a human vaccine were set back in 2002 when it was pulled from the market due to poor sales."

Although the study showed significant reduction in risk and was the first demonstration of a wildlife vaccination effect for any vector-borne disease, the reduction was not as great as the investigators had hoped.

A surprising result was that mice are not as important in maintaining the Lyme disease bacterium in nature as previous studies showed. "If only mice were responsible for infecting the ticks, we would have seen a much greater reduction," Fish explained. "We now believe that mice are responsible for only 27 to 55 percent of the infection found in ticks. This changes our view on how Lyme disease is circulated between wildlife and ticks."

Fish said that in addition to mice, other animals must receive Lyme disease vaccination in order to further reduce risk to humans. Oral vaccines, similar to those currently used against rabies, could be developed for Lyme and other vector-borne human diseases that are maintained by wildlife, including West Nile encephalitis.

Co-authors include J. Timothy Woolton, Jonas Bunkis and Maria Gabriela Luna.

Citation: PNAS Vol. 101 No. 50 December 13, 2004.