Sep. 15, 1998 COLUMBIA, Mo. - As two drug companies are racing for approval of a new vaccine to prevent Lyme disease, a similarly dangerous tick-borne illness, ehrlichiosis, is quickly spreading in the southeastern, mid-Atlantic and south-central regions of the nation. Researchers at the University of Missouri-Columbia College of Veterinary Medicine are studying the pathogen and hope to suggest an intervention, possibly a vaccine.
With the help of a $108,000 grant from the National Institutes of Health, lead researcher Gerald Buening, MU associate dean for research and postdoctorate studies in veterinary medicine, is creating an animal model to aid in studying how the disease affects humans. By studying genetically identical mice infected with Ehrlichia chaffeensis, the bacteria that causes ehrlichiosis, Buening and his team can track the progression of the disease from exposure to responses to antibiotic treatment. Knowing what happens before human symptoms begin will help the team to improve detection and control of infections in humans, and possibly develop improved treatment to prevent the illness.
"Treatments like the vaccine for Lyme disease will be beneficial in high risk areas--parts of the country where most of the disease cases occur," Buening said. "The number of diagnosed cases of ehrlichiosis doesn't warrant the use of a vaccine yet. We are fortunate that the disease can be treated if diagnosed quickly, and the animal model we are creating will contribute to earlier detection and effective treatment."
Symptoms of ehrlichiosis include fever, headache, muscle pain, anorexia, nausea and in some cases, a rash. Clinical laboratory abnormalities that can help doctors identify the disease include leukopenia (an abnormally low white blood cell count) and thrombocytopenia (a reduction in blood clotting platelet cells). While not as widespread as Lyme disease, with 70,000 cases so far versus more than 400 cases and 12 deaths due to ehrlichiosis, ehrlichiosis is considered more dangerous than Lyme disease because it can be fatal if not recognized, diagnosed and treated immediately. Ehrlichiosis also is "newer" than Lyme disease. It has been around for only a decade, while Lyme disease has been around for almost two decades.
It is natural to study ehrlichiosis in Missouri because the majority of reported cases have been in the state. "Some diseases (like ehrlichiosis) spread as the deer population increases and the interaction between humans and wildlife increases," Buening said. Deer are a reservoir for the bacteria, and humans become infected when they are bitten by a tick that has been on an infected deer. "Ticks transmit the disease from deer to humans. The ticks may be infected for a period of time, so they do not need to go directly from deer to humans," Buening said. If a tick is removed immediately, there's only a slight chance of disease; it takes 24 to 48 hours to infect a human.
Awareness and prevention are the keys to protecting yourself from tick-borne disease. Researchers warn people who walk in tick-infested areas to wear protective clothing, use bug repellant and thoroughly inspect their bodies for attached ticks every four to six hours.
Buening and his colleagues in the MU College of Veterinary Medicine are collaborating on this project with the following MU School of Medicine faculty members: William E. Roland, assistant professor of clinical medicine; E. Dale Everett, professor of medicine; and Gregory A. McDonald, associate professor of molecular biology and immunology. They also are working with Lonnie Hansen, a wildlife research biologist in the Missouri Department of Conservation.
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