MINNEAPOLISResearchers have cultivated the bacterium that they believe causes human granulocytic ehrlichiosis, but they have not determined whether it is a new species, according to a recent report.
The ability to cultivate the HGE organism "opens up the possibility of studying the organism in a much more thorough manner," said lead investigator Jesse L. Goodman, MD, Associate Professor of Medicine at the University of Minnesota here. Researchers need to grow the organism to examine how it causes disease and to develop diagnostic tests and treatments for HGE.
"Before we were able to cultivate this [organism], people interested in this disease really had very little to work with," Goodman said.
Researchers believe that the bacterium is transmitted by Ixodes scapularis ticks, the same ticks that serve as a vector for Borrelia burgdorferi the bacterium that causes Lyme disease. Genetic analyses indicate that the HGE bacterium is closely related to Ehrlichia equi and Ehrlichia phagocytophila, which cause illness in animals, said the report, which appeared in The New England Journal of Medicine.
First described in 1994, HGE is an acute febrile illness that sometimes is fatal. Most confirmed cases have occurred in people living in the upper Midwest.
In a recent report in the Journal of the American Medical Association, Johan S. Bakken, MD, and colleagues characterized HGE and evaluated diagnostic methods for the illness. The investigators studied 41 patients from Wisconsin and Minnesota who had a laboratory diagnosis of HGE from June 1990 to May 1995. During the acute illness, all 41 patients had a fever of 37.6° C or higher, and 40 of 41 patients had rigors, sweats, headache, malaise, and myalgias. Most had varying combinations of leukopenia, thrombocytopenia, and anemia.
"Human granulocytic ehrlichiosis should be suspected in previously healthy individuals who suddenly develop a febrile influenza-like illness after outdoor activity in the upper Midwest," the report stated. "A history of tick exposure or an actual tick bite during the preceding weeks should further strengthen the suspicion of HGE."
For more information, see:
- 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.
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