Diversity of tick species biting humans in an emerging area for Lyme disease

Background. Although most tick bites in humans in areas of the northeastern United States in which Lyme disease is highly endemic are due to Ixodes dammini, no study documents the frequency of I. dammini bites in low-prevalence or emerging areas for Lyme disease. Data on the proportion of tick bites in humans that are due to I. dammini in a region may have implications for public health policy and clinical management. Methods. A statewide survey of the tick species that parasitized humans in Maine was conducted during 1989 and 1990. Tick submissions from throughout the state were elicited through media announcements. All ticks that had been removed from humans were identified, and data were collected that included bite seasonality and geography and demographics of tick bite victims. Results. Of 709 ticks submitted, only 17% were I. dammini. Ixodes cookei, a vector for Powassan encephalitis, accounted for 34% of bites, and Dermacentor variabilis accounted for 45%. Other tick species were occasionally implicated. Conclusions. The likelihood that a tick bite was due to I. dammini was lower in Maine than in areas in the northeastern United States in which Lyme disease is highly endemic. Other tick vectors, associated with diseases other than Lyme disease, were more frequently implicated. Regional tick bite surveys may prove useful in assessing the risk of Lyme disease following a tick bite.