The disease, human granulocytic ehrlichiosis (HGE), is spread by ticks that bite the animals. The ticks also can transmit HGE directly to humans the same way.
"This finding suggests that many people in these areas may be at risk for HGE infection from tick bites, and doctors and patients should stay alert to this possibility," says Jennifer Walls, a pathology student and author of a presentation at this year's annual meeting of the American Society for Microbiology.
In a study funded by the National Institute of Allergy and Infectious Diseases, Walls showed that blood samples from 20 of 43 white-tailed deer and 6 of 80 black bears had signs of current or prior infection.
In one study of Midwesterners with ehrlichiosis, 56 percent of patients were hospitalized and 2 percent died. In serious cases, the body's defense systems become too weak to fight off infections by viruses, fungi and bacteria that can cause fatal complications.
"Patients with ehrlichiosis start with very general, flu-like symptoms--fever, headaches, muscle aches, and most doctors say, It's a virus! Go home and get some rest.' That's scary because there's a special antibiotic that can cure patients in 24 to 48 hours if the infection is caught early," says J. Stephen Dumler, M.D., a Hopkins associate professor of pathology and a study co-author.
After tracking infections that ranged from mild and flu-like to a serious weakening of the body's defenses, Dumler and colleagues identified the bacteria responsible for HGE while he was at the University of Maryland in 1993.
He recommends several steps for reducing the chances of infection with HGE and other tick-borne diseases.
"Avoid areas where ticks proliferate, such as places overgrown with low-lying plant life," he advises. "If you can't do that, wear more clothing or a tick repellent. If you find a tick bite, remove the tick as quickly as possible. This reduces the chance of infection. And if you have flu-like symptoms after a tick bite, make sure your doctor considers the possibility of an HGE infection."
Dumler's group currently is studying HGE in white-footed mice, which appear to be a "reservoir" for the disease.
"HGE doesn't transmit well to tick eggs, so it needs other ways to spread," says Dumler. "The white-footed mouse appears to provide this. When bitten by an infected tick, the mouse becomes infected and can spread HGE to other ticks that bite it. When you consider that a typical mouse may have as many as 50 to 100 tick bites at a time, that's a pretty good way to spread."