Ehrlichia – New Species Identified

August 2011

Mayo Medical Laboratories has detected a new pathogenic Ehrlichia species. The new species was first detected in four patients from Minnesota and Wisconsin in 2009. More than twenty-five patients with the same infection have been identified since then. Analysis at Mayo Clinic and by the Centers for Disease Control and Prevention (CDC) has shown this new species to be closely related to Ehrlichia muris, a species not previously reported in North America.

In addition to the reported human cases, evidence of the bacterium has been found in deer ticks (Ixodes scapularis) and white-footed mice (Peromyscus leucopus) collected from Minnesota and Wisconsin. Detection of this new Ehrlichia species is the subject of an article just published in the New England Journal of Medicine.¹

Video

Emergence of a New Pathogenic Ehrlichia Species by Bobbi S. Pritt, MD, Director of the Clinical Virology and Parasitology Laboratories in the Division of Clinical Microbiology, Mayo Clinic

Test

Ehrlichia/Anaplasma, Molecular Detection, PCR, Blood #84319

• Useful for evaluating patients suspected of human granulocytic anaplasmosis or human ehrlichiosis

Clinical Information

Ehrlichia are intracellular bacteria transmitted by ticks to humans and animals.  In humans, Ehrlichia bacteria infect and kill white blood cells, and may cause disease in the lungs, kidneys, intestinal tract, and brain. Rarely, death may result from infection.

Each of the four patients in whom the new species was first detected had presented to their physician with fever, headache and body aches, and laboratory analysis showed decreased numbers of white blood cells in their blood.  Three of them also had low platelets, and two had evidence of liver injury. The four patients all had symptoms consistent with ehrlichiosis and recovered following treatment with doxycycline, an antibiotic used to treat Ehrlichia infection.

Prior to this report, human disease caused by any Ehrlichia species was not thought to be present in Minnesota and Wisconsin. Therefore, physicians need to know to test for ehrlichiosis in these two states so the diagnosis is not missed. Commercially available serologic assays for Ehrlichia chaffeensis or Anaplasma phagocytophilum do not provide a specific diagnosis and may miss cases. An antibody detection method for the new bacteria has also been developed by the CDC, but is not widely available. PCR, which detects DNA from the new Ehrlichia species in peripheral blood specimens, is the preferred method for detecting acute disease.

Clinical References

1. Pritt BS, Sloan LM, Hoang Johnson DK et al: Emergence of a New Pathogenic Ehrlichia Species, Wisconsin and Minnesota, 2009. N Eng J Med 2011 Aug4;28-35

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