Ref: MIDTERM REPORT- 1999

This report summarizes data from the Rocky Mountain Spotted Fever and Lyme Disease Tick Testing Program for the period January 1 - June 30, 1999. During this period we received 544 ticks for identification and testing. This was 227 more ticks than we received last year during the same time period.

These ticks were submitted from 58 counties, 4 other states, and one other country. Counties submitting the greatest numbers of ticks were Lawrence (67), Newton (43), Porter (40), Delaware (31), Bartholomew (30), Franklin (30), Lake (25), Posey (20), and Vanderburgh (17) (Fig. 1). Ticks were also received from Illinois, Kentucky, Ohio, Virginia, and Mexico.

The seasonal distribution for ticks thus far in 1999 is similar to those of past years, with the peak number of submissions occurring in May (268 ticks). In April we received 154 ticks and in June we received 111 ticks (Fig. 2). This is the most ticks received during the month of April since 1989.

Three hundred and fifty-three (65%) of the ticks submitted were identified as the American dog tick, Dermacentor variabilis. One hundred and thirteen (21%) of the ticks were identified as the lone star tick, Amblyomma americanum (Fig. 3). The remaining 14% comprised 3 species: Ixodes scapularis (62), Ixodes cookei(8), Rhipicephalus sanguineus (4) (Fig. 4). Eighty percent of all ticks received were collected from humans, 13% from dogs and 7% from other hosts or habitats (Fig. 5).

Of the 544 ticks received, 155 (28%) arrived dead and could not be tested (Fig. 6). Of the 389 received alive, 345 (89%) were potential Rocky Mountain spotted fever vectors (D. variabilis or A. americanum) that had been attached to humans, and thus, were tested. Six of these ticks (1.7%) reacted positively to our FITC labeled anti-Rickettsia rickettsii antibody. In each case, the appropriate parties were immediately notified of the positive test results. Two I. scapularis ticks that were attached to humans were tested for Borrelia burgdorferi, the Lyme disease agent, and both were negative.

In June, we discovered an extensive population of I. scapularis, the Lyme disease tick, in Porter County, in the vicinity of the Dunes National Lakeshore. While the population seems well established we have not completed the testing of these ticks for Lyme disease spirochetes. Nonetheless, health officials should be aware of the possibility of tick exposure at this public recreation facility.