Paul G. Auwaerter, MD


October 19, 2011

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Hello. This is Paul Auwaerter from Johns Hopkins University School of Medicine for Medscape Infectious Diseases. Two new tick-borne human pathogens have been reported that you may wish to fold into your clinical practice considerations, although tests are not yet commercially available.

The first report is a rather high-profile article in The New England Journal of Medicine[1] that describes a new ehrlichial infection that afflicted 4 patients in Minnesota and Wisconsin with a presentation typical of Ehrlichia species fever: headache, low white blood cell count, and low platelet count. This presentation was [caused by] Ehrlichia muris, [which was] not thought to infect humans and most interestingly was transmitted by the Ixodes scapularis tick, which is the same tick that transmits Lyme disease. Ehrlichia chaffeensis serologies may be positive, as they were in 3 of these 4 patients, so these tests can be misleading. It seems that Ehrlichia [species infection] is now transmissible by deer ticks as opposed to only by lone star ticks, according to the conventional wisdom in the past.

The second report is by Platonov and colleagues[2] in Emerging Infectious Diseases and looked at 46 patients in Russia who had mostly a relapsing fever presentation. However, 10% of these patients had a rash that was similar to erythema migrans, and it seems that the infecting agent was Borrelia miyamotoi, which is a distant relative of Borrelia burgdorferi, the agent of Lyme disease.

Also of interest in this paper were reports of studies conducted by Derlund Fish, one of the co-authors, who found this exact Borrelia species present in ticks in the northeastern United States. Perhaps, although the information is not yet present, it is possible that a certain percentage of patients who were thought to have Lyme disease caused by Borrelia burgdorferi might in fact have erythema migrans from Borrelia miyamotoi.

This is not yet known, but hopefully will be investigated soon. This demonstrates some of the powers that new molecular diagnostics are bringing to the investigation of infectious diseases beyond just traditional serology and culturing techniques. The second attribute is the tick intestinal tract, which has a host of organisms that can serve as pathogens, and indeed we are finding more as time goes on.

I want to extend a cautionary note that in each of these cases, there is fairly clear-cut evidence of infection: fever, headache, rash, and so on. Some have taken the leap that these pathogens in the tick gut might explain so-called "chronic Lyme disease" or problems such as chronic fatigue, muscle aches, headaches, and brain fog -- the neurocognitive symptoms. Whether those symptoms are caused by chronic fatigue syndrome or other entities is not yet clear.

A number of trials of antibiotics, all of which we use to treat, for example, Ehrlichia species or even Borrelia species, have not [shown any of these medications] to be successful in patients who have had persistent symptoms from Lyme disease.

Although there might be an attractive hypothesis here, it is far from proven. It is exciting that we are learning about new potential pathogens, and our commercial assays will need to catch up to give a better discrete diagnosis. However, this is not yet the explanation for many patients who unfortunately have persistent symptoms and are given antibiotics, probably inappropriately in many cases. You can find more information in the suggested readings below by myself and Dr. Feder.


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