Geographic distribution of ticks (Acari: Ixodidae) in Iowa with emphasis on Ixodes scapularis and their infection with Borrelia burgdorferi.

In Iowa, public concern regarding Lyme disease has increased markedly over the last decade. In response to these concerns, a statewide surveillance program was initiated in 1990 based on ticks received by the Department of Entomology at Iowa State University. Ticks were received from health care professionals, state government agencies, and the general public. A total of 5,343 ticks from all 99 Iowa counties were identified during the 12 years of this study. Dermacentor variabilis was the most numerous species, followed by Amblyomma americanum, and Ixodes scapularis. Dermacentor variabilis were distributed statewide, but A. americanum came primarily from southern Iowa counties. Prior to 1996, most I. scapularis came from counties along the Mississippi River. In the last 5 years, I. scapularis have been received from several counties in central and western Iowa and there is molecular evidence of infection with Borrelia burgdorferi in a substantial percentage of ticks. All I. scapularis were tested for the presence of B. burgdorferi. During the 12 years of this study, the presence of B. burgdorferi in I. scapularis varied from a low of zero percent in 1991-1995 to 18% in 1996. On average, fewer than 10% of all ticks examined per year were I. scapularis. In the 2000 tick season, the number of I. scapularis per year increased to 22% of submissions. This species further increased to 36.6% of ticks received in 2002.