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Release: Aug. 7, 2000

UI researchers track new tick-borne disease in Iowa

IOWA CITY, Iowa -- With the help of more than 2,000 Iowa deer hunters, researchers at the University of Iowa have tracked the migration of a new tick-borne disease into Iowa.

An article in a recent issue of Emerging Infectious Diseases, a journal published by the Centers for Disease Control and Prevention, features this unusual collaboration between scientists and game hunters to trace the route of this potentially fatal disease.

Human monocytic ehrlichiosis (HME) is a newly recognized disease caused by the bacterium Ehrlichia chaffeensis and carried by the Lone Star tick. The tick's preferred host is the white-tailed deer, but it does occasionally bite humans. Deer are not affected by Ehrlichia, but they do produce antibodies to the bacteria when bitten by an infected tick.

HME, a potentially life-threatening disease if not treated early, was first recognized in Arkansas in 1986. Human cases of this disease have been reported in Illinois, Missouri and several other states south of Iowa, but it has not yet been reported in Iowa.

Deer hunters from across Iowa were asked by researchers to collect small samples of blood from white-tailed deer and record the location where the deer was killed. The samples were then mailed to the UI Hygienic Laboratory and tested for antibodies. The deer survey, done in 1994 and again in 1996, showed an increase in the prevalence of seropositive deer -- deer that have been exposed to Ehrlichia -- especially in Iowa's southern counties.

"These data indicate that Ehrlichia may be moving north into Iowa from Missouri," said Peter Thorne, professor of occupational and environmental health in the UI College of Public Health.

In fact, a map of the prevalence of deer exposed to Ehrlichia shows a gradient running from south to north, with the highest rates in Iowa's southernmost counties. Prevalence also increased from 1994 to 1996. The figures are adjusted for changes in deer population by region.

Symptoms of HME range from a mild, flu-like syndrome to a severe, life-threatening illness. It is difficult to diagnose, but can be treated with antibiotics once a diagnosis is made. Because of its vague symptoms, tracking Ehrlichia in deer, rather than in humans, made sense to researcher Linda Mueller-Anneling, who was at the UI Hygienic Lab at the time of the study.

"By looking at antibodies in deer, you can follow the disease, even if deer don't get sick from it," Mueller-Anneling said. "Now we know that there are definitely ticks in Iowa that carry Ehrlichia, and we can take appropriate measures to protect humans.