New Tick Borne Ehrlichia Bacterium Identified in Midwest United States

by Dr Sam Girgis on August 6, 2011

Ehrlichiosis is a tick borne infectious disease that is caused by an obligate intracellular Gram negative bacteria.  The bacteria are transmitted to humans by the bite of a tick which harbors the bacteria.  The Amblyomma americanum, Ixodes scapularis, and Ixodes pacificus ticks transmit the disease in the United States.  The bacteria usually infects white blood cells and results in a lymphopenia, or low white blood cell count.  Symptoms of the illness can include fever, headache, muscle aches, and rash at the site of the tick bite.  In addition, more severe illness can result and is associated with renal, gastrointestinal, and neurological sequelae.  In rare cases, the disease can cause death of the patient if not treated appropriately.  Researchers lead by Dr. Bobbi Pritt have described the identification of a new pathogenic Ehrlichia species that has caused an Ehrlichiosis type illness in four patients in the Midwest states of Wisconsin and Minnesota.  The results of their research were published online in the New England Journal of Medicine.  The researchers used molecular methods, culturing, and serologic testing to identify the new disease entity.  Four cases of Ehrlichiosis in Minnesota or Wisconsin, which were not caused by the known bacteria E. chaffeensis or E. ewingii, were identified for further investigation.   The four patients presents with symptoms that were typical for Ehrlichiosis and included fever, malaise, headache, and lymphopenia.  In addition, three patients also had thrombocytopenia, and two had elevated liver enzymes.  The patients were treated with doxycycline antibiotics and had a complete recovery from the illness.  The investigators collected 697 Ixodes scapularis ticks from the Minnesota or Wisconsin region and 17 were found to be positive for the new species of bacteria using polymerase chain reaction testing methods.  Further genetic testing showed that the new species of bacteria was related to E. muris and has been termed Ehrlichia Wisconsin HM543746.  The authors wrote, “we have characterized a newly discovered ehrlichia species with supportive clinical, epidemiologic, culture, DNA-sequence, and vector data. Further assessment of the ecologic, epidemiologic, and clinical features of the infection caused by this species is required to facilitate its distinction from other known tickborne infections in this region. To guide diagnostic testing and treatment, physicians should be aware that a novel pathogenic ehrlichia agent is present in Minnesota and Wisconsin and that organism specific PCR and serologic testing can be used to identify the cause of suspected infections”.


Bobbi S. Pritt et al. “Emergence of a New Pathogenic Ehrlichia Species, Wisconsin and Minnesota, 2009N Engl J Med 2011; 365:422-429 August 4, 2011

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