Close to 400 human cases of Lyme disease and several --cases of Babesiosis and Human Granulocytic Ehrlichiosis (HGE) are reported in the State of Wisconsin each year. For several years, Lyme disease has been known to be highly endemic in the northwestern region of the state. But little is known about the co-infection rate of these three diseases. Past deer surveys have suggested no existence of deer ticks in the eastern part of Wisconsin, except Marinette County near Green Bay. However, I recently identified deer ticks on mice in the Lower Kettle Moraine, and 3.6 percent were found infected with Borrelia burgdorferi. Deer tick populations have progressively been spreading to Central Wisconsin. It is important to investigate more thoroughly the population structure of deer ticks and associated diseases. Study sites in Wisconsin will include Dunn County, Portage County and Marinette County. For three years, adult ticks will be collected in each fall season by dragging flags. The microgeographic distribution of Ixodes scapularis will be determined. The 16S rDNA sequence of the ticks will be compared to determine whether gene flow exists among these areas. The DNA from crushed tick parts will also be tested for tick-borne pathogens using the polymerase chain reaction (PCR). The genes targeted will be OspB for B. burgdorferi, the 16S-like gene for Babesia microti and the 1 6S rRNA gene for Ehrlichia (HGE). DNA sequencing for all three pathogens will be used for species verification. The microgeographic distribution and co-infection rates of tick-borne diseases, from their main vector are major contributions to the understanding of the spread of tick-borne diseases in Wisconsin. A Lyme disease vaccine is now available to the public, which is a recombinant form that includes the ospA gene of a New York B. burgdorferi strain. I recently discovered a highly mutated strain from southeastern Wisconsin. It is possible that the vaccine may not be effective against this strain. I propose to monitor the frequency and spread of this strain in northwestern, central, and northeastern Wisconsin. If this strain is prevalent in this state, vaccine developers should investigate the efficacy of their vaccine on this strain.