Researchers discover new bacterium causing tick-borne ehrlichiosis in Wisconsin, Minnesota

Rochester, Minn. --

A new tick-borne bacterium causing ehrlichiosis has been discovered in Wisconsin and Minnesota.

In fact, a multi-institutional collaboration with the Mayo Clinic, Centers for Disease Control and Prevention (CDC), University of Wisconsin and University of Minnesota presented the finding in the

New England Journal of Medicine

. Two CDC veterinarians, Drs. Kristina McElroy and Jennifer McQuiston, were cited as authors in the 24-person research team making the discovery.

The new bacterium from

Ixodes scapularis

(deer ticks) has not yet been named, but it has infected more than 25 people in Minnesota and Wisconsin. The bacterium causes a feverish illness in people, the researchers say. Culture and genetic analyses were used to identify the new bacterium, according to a report from the Mayo Clinic.

"Before this report, human ehrlichiosis was thought to be very rare or absent in Minnesota and Wisconsin," says Bobbi Pritt, MD, a Mayo Clinic microbiologist and director of the Clinical Parasitology and Virology Laboratories who helped coordinate the multi-agency team.

All four patients described in the New England Journal of Medicine article suffered fever and fatigue. One patient, who had already received a bilateral lung transplant, was hospitalized briefly for his illness. All four patients recovered following antibiotic treatment with doxycycline, the drug of choice for treating ehrlichiosis.

"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," says co-author Susan Paskewitz, PhD, an entomologist at the University of Wisconsin-Madison.

While thousands of blood samples from multiple U.S. states have been screened, the bacterium has been detected only in specimens collected from Wisconsin and Minnesota. Thousands of ticks from multiple states have also been analyzed, and only those from the two states have been confirmed as carriers.

Traditional blood antibody tests may offer misleading results and fail to accurately identify the new species, the researchers report. But a specific antibody test for the new bacterium has been developed by CDC but isn't widely available. However, a molecular blood test that detects DNA from the new Ehrlichia species is the preferred method for detecting this disease in symptomatic patients.

Genetically, the new bacterium bears closest similarity to another species of Ehrlichia --

E. muris

-- that infects small rodents and deer in Eastern Europe and Asia.

E. muris

rarely infects humans, and no cases have been reported in North America.

Other authors include Lynne M. Sloan; Matthew Binnicker, PhD; Scott Cunningham; Mark Wilhelm, MD; and Robin Patel, MD, all of Mayo Clinic; Ulrike Munderloh, PhD, and Curtis M. Nelson, both of the University of Minnesota; David Neitzel and Gongping Liu, PhD, both of the Minnesota Department of Health; Diep Hoang Johnson; Jevon McFadden, MD; Christopher Steward; and Jeffrey Davis, MD, all of the Wisconsin Division of Public Health; Joni Franson; Scott Martin, MD; and Vipul Trivedi, MD, all of Mayo Clinic Health System in Eau Claire; Kay Bogumill, RN, of the Eau Claire County Health Department; Mary Bjorgaard, RN, of the Burnett County (Wis.) Department of Health and Human Services; David Warshauer, PhD, of the Wisconsin State Laboratory of Hygiene; Kristina McElroy, DVM; William Nicholson, PhD; Jennifer McQuiston, DVM; and Marina Eremeeva, MD, PhD, ScD, all of the Centers for Disease Control and Prevention.