SAN ANTONIO — Physicians who see patients presenting with extreme localized pain beginning a few days after a tick bite have a new reason to consider the possibility of ehrlichiosis, based on findings reported at a meeting of the Southwest Conference on Diseases in Nature Transmissible to Man.
Researchers from the Centers for Disease Control and Prevention have discovered a possible new Ehrlichia species found to cause illness in humans, as well as goats.
The vector for the disease is the domestic Lone Star tick.
Amanda Loftis, D.V.M., of the CDC's medical entomology laboratory in Atlanta, reported a human case that she said could be a “divergent strain” of the bacterium Ehrlichia ruminantium, which is on the U.S. Department of Agriculture's watch list of foreign pathogens, or a new Ehrlichia species.
Dr. Loftis said the new bacterium is genetically similar to E. ruminantium, which is considered common in Africa and the Caribbean but so far unreported in the United States.
The new agent causes only mild illness in humans and animals, unlike E. ruminantium, which causes heartwater disease.
Five days after removing a tick from his upper arm, the patient, an Atlanta man, experienced extreme neck pain that was unresponsive to NSAIDs. He presented to a physician 4 weeks after removing the tick.
The physician suspected tickborne illness, took a blood sample, and administered doxycycline; the patient reported significant improvement in neck pain after 48–60 hours, Dr. Loftis said.
Dr. Loftis and her colleagues first discovered the new agent when they tested local ticks on a laboratory goat that subsequently became mildly ill. Genetic tests for five genes showed that the agent infecting the goat was highly similar to E. ruminantium but not identical to any described strains.
Furthermore, the CDC performed DNA tests on the patient's blood and found Ehrlichia DNA identical to sequences found in the goat and in wild Lone Star ticks.
No other bacterial DNA were detected, Dr. Loftis reported at the meeting, held in conjunction with the International Conference on Diseases in Nature Communicable to Man.
“Nothing like this has ever been reported from the United States,” Dr. Loftis said.
“The scary thing is that the Hartsfield International Airport, a U.S.D.A. port of entry for import of animals, is very close to our collection site. Both are within the Atlanta metro area—so we have to ask the question, where did this come from?” she said.
There are 13 species of tick that can be vectors of E. ruminantium, but only 3 of these species live in the United States, she noted.