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Date: Wednesday, January 24, 1996 For Immediate Release Contact: NIAID (301) 496-5717
Researchers supported by the National Institute of Allergy and Infectious Diseases (NIAID) have successfully isolated the organism that causes human granulocytic ehrlichiosis (HGE), a newly recognized and sometimes fatal infection transmitted to people by ticks.
Jesse L. Goodman, M.D., of the University of Minnesota and his colleagues are the firstresearchers to grow the yet-unnamed bacterium in laboratory cell cultures, using blood frompatients with HGE. They report their findings in the Jan. 25, 1996 issue of The New EnglandJournal of Medicine.
"Little is known about the agent that causes HGE, because until recently we have been unable to grow this intracellular pathogen in the laboratory," says Dr. Goodman. "Now that this bacterium has been isolated from patients, we can develop improved diagnostic tools and treatments, as well as better understand the biology and epidemiology of this emerging infection."
"As has been the case with other emerging diseases such as Lyme disease, NIAID-supported investigators have worked quickly to understand HGE, building on our long-standing investment in fundamental biomedical research," says Anthony S. Fauci, M.D., NIAID director.
HGE was first described in 1994 in patients in Minnesota and Wisconsin. Subsequently, cases have been reported in California, Florida, Maryland, Massachusetts and New York. Several dozen cases have been reported in the scientific literature, but the true prevalence of the disease is probably much higher, says Dr. Goodman.
HGE appears to be transmitted by deer ticks, which also can transmit Lyme disease. It has been suggested that HGE may also be transmitted by dog ticks. Physicians have observed patients infected by two or more tick-borne infections at once, which can make diagnosis and treatment decisions difficult.
"A diagnosis of HGE may be missed when there is simultaneous infection with the Lyme bacterium, which usually causes a rash that is not typically seen in people with HGE," says Dr. Goodman. "In such cases, patients may receive treatment for Lyme disease such as amoxicillin that is not effective against HGE. The emergence of HGE makes it critical that physicians consider this infection in the differential diagnosis of an acute illness with fever occurring after a possible tick exposure."
The HGE bacterium is closely related to bacteria of the genus Ehrlichia, including E.chaffeensis, which causes a human disease (ehrlichiosis) that is similar to HGE. Ehrlichiosis was first observed in humans in 1986, and E. chaffeensis was isolated in 1991. Other Ehrlichia cause diseases in dogs, horses, sheep and cattle.
Ehrlichia grow inside of cells; the HGE bacterium grows inside immune system cells called granulocytes, while E. chaffeensis favors different immune system cells called monocytes.
Signs and symptoms of both HGE and ehrlichiosis due to E. chaffeensis are similar. They include fever, chills, headaches, muscle aches, nausea and vomiting. Laboratory findings often include elevated liver enzymes, and a decrease in a patient's blood platelets and white blood cells. Both diseases typically last one to two weeks, and most patients who receive treatment recover without long-lasting complications. However, a small proportion of patients with HGE or ehrlichiosis due to E. chaffeensis may suffer more severe symptoms, such as kidney failure, respiratory problems or meningitis. The case-fatality rate for both diseases may be as high as 5 percent. Severe infections and death are most likely in older people, and in those who are not promptly treated. HGE and disease caused by E. chaffeensis are generally treated with a minimum seven-day course of tetracycline or doxycycline.
Because of the rise in tick-borne infections, including Lyme disease, Rocky Mountain Spotted Fever and diseases due to Ehrlichia such as HGE, avoiding exposure to ticks is important. In an editorial in the same issue of The New England Journal of Medicine, William Schaffner, M.D., of Vanderbilt University, and Steven M. Standaert, M.D., of the Association pour l'Aide a la Medecine Preventive (France), write, "The use of insect repellents reduces the risk of infection. Other precautions that discourage the attachment and feeding of ticks, such as the wearing of light-colored clothing, long pants and long-sleeved shirts, and thorough examination of the skin after walking in the woods or fields may also be helpful."
Dr. Goodman's co-authors include Curtis Nelson, B.A., Timothy J. Kurtti, Ph.D., and Ulrike G. Munderloh, D.V.M., Ph.D., of the University of Minnesota; Blaise Vitale, M.D., of the Grantsburg Clinic, Grantsburg, Wis.; John E. Madigan, D.V.M., of the University of California, Davis; and J. Stephen Dumler, M.D., of the University of Maryland School of Medicine, Baltimore.
The research by Dr. Goodman and colleagues is supported as part of NIAID's comprehensive research agenda to enhance the nation's ability to detect and control emerging microbes such as HGE. The goals of this agenda are to:
1) Develop a research and training infrastructure capable of responding expeditiously to infectious disease emergencies.
2) Expand basic and applied research on ecologic and environmental factors influencing emergence.
3) Expand basic and applied research on microbial changes and adaptations influencing emergence.
4) Expand basic and applied research on host interactions with emerging pathogens.
5) Support development and testing of control strategies for specific diseases with potential for emergence.
NIAID is a component of the National Institutes of Health. NIAID conducts and supports research aimed at preventing, diagnosing and treating illnesses such as AIDS and other sexually transmitted diseases, tuberculosis, asthma and allergies. NIH is an agency of the U.S. Public Health Service, part of the Department of Health and Human Services.
References:
Goodman JL, Nelson C, Vitale B, et al. Direct cultivation of the causative agent of human granulocytic ehrlichiosis. N Engl J Med 1996;334:209-15. Schaffner W, Standaert SM. Ehrlichiosis - in pursuit of an emerging infection. N Engl J Med 1996;334:262-3.
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