What is Ehrlichia sp. Wisconsin (sometimes referred to as EML)?
In 2009, a new species of Ehrlichia was detected in four human patients (3 from Wisconsin, 1 from Minnesota) using molecular laboratory testing techniques. This new bacterial species was found to be most closely related to Ehrlichia muris. This newly identified species has been called Ehrlichia muris-like (EML) and will likely be renamed as a subspecies called Ehrlichia muris eauclairensis. [Pritt et al. Emergence of a new pathogenic Ehrlichia species, Wisconsin and Minnesota, 2009. New England Journal of Medicine 365(5):422-429. 2011. http://www.nejm.org].
Where is Ehrlichia sp. Wisconsin found in Wisconsin?
Figure 1. Infection rates for Ehrlichia sp. Wisconsin (also referred to as Ehrlichia muris-like or EML) in Ixodes scapularis ticks collected from animals brought to veterinary, human society and rehabilitator partners. Since the initial discovery of this novel Ehrlichia bacteria in 2009, the majority of human cases in Wisconsin have been reported in counties in western-central and northwestern Wisconsin. Historical and current data for human cases can be found at http://www.dhs.wisconsin.gov/communicable/tickborne/AandE/EMLdatamaps.htm.
How is Ehrlichia sp. Wisconsin transmitted?
The organism has been detected in some deer ticks (Ixodes scapularis) which were collected and tested in Wisconsin and Minnesota but it is still unclear what role this particular tick species plays in the transmission of this bacteria within this geographic region.
What are the Clinical Signs and Symptoms of Ehrlichia sp. Wisconsin infections?
Patients in the Pritt et al. (2011) study infected with the agent reported to their medical provider varying clinical signs and symptoms including:
Fever, malaise or general discomfort, fatigue, headache, nausea and vomiting.
Clinical laboratory findings in patients included increased liver enzyme levels, a reduction in platelet numbers (thrombocytopenia) and reduced numbers of particular white blood cells (e.g. such as lymphocytes).
Two patients had a previous history of organ transplant and were taking immunosuppressive drugs at the time of diagnosis.
All patients reported peridomestic (e.g. activities around the yard such as mowing the lawn) and recreational activities in wooded areas which may have increased their exposure to ticks.
How is Ehrlichia sp. Wisconsin Diagnosed?
If you think you may be sick with a tick-borne illness or may have been bitten by a tick please contact your physician or medical provider. Diagnosis of tick-borne diseases such as ehrlichiosis, anaplasmosis and Lyme disease are based on a thorough medical history, possible exposure to established high-risk areas for these infectious organisms or tick vectors which carry them where you live or spend time outdoors and physician observed clinical signs and symptoms as well as accompanying diagnostic laboratory methods to support the diagnosis.
Molecular laboratory diagnostic testing, specifically via polymerase chain reaction (PCR) is the current laboratory test of choice for diagnosing this newly recognized pathogen due to serologic cross-reactivity with other similar Ehrlichia species such as Ehrlichia chaffeensis, the bacteria which causes human monocytic ehrlichiosis. Serologic testing is used to indirectly detect exposure to an infectious agent such as a bacteria or virus. Laboratory tests, specifically serologic tests, can be used to detect the body’s response to exposure to an infectious agent via the detection of antibodies. After exposure to certain infectious agents (e.g. viruses or bacteria) the immune system in the body may produce antibodies and serologic tests can be used to detect the production of antibodies to these infectious agents in the blood or other body fluids such as cerebrospinal fluid (CSF). These serologic tests are not perfect and cross-reactivity may occur between similarly related bacteria or viruses or other infectious agents causing a false positive result for a particular laboratory test.
Until a more specific and reliable serologic test is available for the infection, currently the most rapid and reliable laboratory detection method is via real-time polymerase chain reaction (PCR) to detect the organism directly in a blood sample in a patient suspected to have a tick-borne disease.
How is the Infection Treated?
All patients in the Pritt et al. (2011) study who were diagnosed with Ehrlichia sp. Wisconsin were successfully treated and recovered with antibiotic treatment with doxycycline.