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Fish Receives CDC Grant to Develop Surface Map Depicting Risk of Transmission to Humans of Bacteria that Causes Lyme Disease

Durland Fish, Ph.D., Professor of Epidemiology in the Division of Epidemiology of Microbial Diseases, has received a $2.9 million, four year grant from the Centers for Disease Control and Prevention (CDC) to develop a surface map depicting human risk of infection in the eastern U.S. from the spirochetal bacteria that causes Lyme disease.

Lyme disease is caused by the bite of ticks of the Ixodes genus that are infected by the spirochetal bacteria Borrelia burgdorferi. Fish and his colleagues will focus on Ixodes scapularis, or deer ticks, which currently live in the northeast and southeast, as well as in parts of the midwest. The range of I. scapularis in the U.S. is steadily increasing, however.

Lyme disease was first recognized in the U.S. in Lyme, Connecticut in the mid-1970’s after the appearance of a cluster of cases of what doctors at first thought was arthritis. The disease is a public health problem in those places where ticks come into contact with people. The number of cases in the U.S. is rising steadily: according to the CDC, the number of cases reported annually has more than doubled since 1991, and annual Lyme disease incidence increased 40% in the years 2001-2002. Fish’s grant is one of ten grants for Lyme disease research that CDC recently awarded in response to this data.

Fish and his colleagues will study nymphal stage I. scapularis (those in the second of three life stages that ticks go through), which have the highest prevalence of Borrelia infection, and thus represent the greatest risk to humans. The field research will take place at ninety-five sites, chosen because they are optimal I. scapularis habitats, throughout the range of I. scapularis in the U.S. from Maine to Texas. “This is the largest field study ever conducted on Lyme disease,” says Fish.

Fish’s team will estimate the population density of host-seeking I. scapularis nymphs and the prevalence of Borrelia infection among them at each site. That data will be analyzed, along with information about variables including climate and vegetation throughout the U.S. range of I. scapularis, using geographic information system (GIS) software, which will allow the researchers to examine the relationships between the variables they are looking at and assist them in generating a surface map of human risk for infection in the eastern U.S. from I. scapularis-borne Borrelia spirochetes.

The map created by Fish and his colleagues will be standardized over a large geographic area, and will represent an improvement over current risk models, which are based on localized, smaller studies and reports of tick findings. In addition, the research will provide information about the times of year during which the risk of contracting Lyme disease is highest.

-Story by Christy Gordon, based on interviews with Maria Diuk-Wasser, postdoctoral associate in the Vector Ecology Laboratory, on May 7, 2004, and Durland Fish, Professor of Epidemiology in the Division of Epidemiology of Microbial Diseases, on May 20, 2004.