So far, the new ehrlichiosis strain has been found only in Minnesota and Wisconsin, even though thousands of ticks from across the U.S. were analyzed.
But it's being spread by deer ticks, previously thought not to carry ehrlichia bacteria. And deer ticks are common in Eastern states.
"Before this report, human ehrlichiosis was thought to be very rare or absent in Minnesota and Wisconsin. Therefore, physicians might not know to look for Ehrlichia infections at all, study leader Bobbi Pritt, MD, director of the clinical parasitology and virology laboratory at Mayo Clinic, says in a news release.
Symptoms of ehrlichiosis vary widely from person to person. They include fever, headache, muscle ache, chills, nausea, vomiting, diarrhea, confusion, red eyes, and rash. Severe symptoms are rare but include difficulty breathing and bleeding disorders. Left untreated, ehrlichiosis is fatal in about 2% of people.
In the Aug. 4 issue of the New England Journal of Medicine, Pritt's team reports on four people who came down with ehrlichiosis due to a previously unknown ehrlichia strain. All four, including two taking immune system-suppressing drugs, recovered after antibiotic treatment.
All told, more than 25 people are known to have been infected with the new bug. So far, the new strain appears to be neither more nor less dangerous than the ehrlichia strains known to be circulating in the U.S. It's closely related to an ehrlichia strain found that infects mice and deer in Eastern Europe and Japan.
In a separate report in the Open Microbiology Journal, Tufts University researcher Sam R. Telford III, SD, notes similar ehrlichia strains can be found in ticks collected in Wisconsin in the 1990s. Thus, the new bug appears to be as common as anaplasma bacteria, which cause the tick-borne disease anaplasmosis and which are also spread by deer ticks.
"It may be that [the new ehrlichia strain] will be found in the U.S. wherever deer ticks are known to be infected by a majority of [tick-borne diseases]," Telford and colleagues suggest.
"As the deer tick population continues to spread and increase across Wisconsin, we are likely to see increasing incidence of this new infection, just as we have seen with Lyme disease and anaplasmosis, which are transmitted by the same tick species," Pritt's colleague Susan Paskewitz, PhD, says in the news release.