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Human granulocytic ehrlichiosis |
Human granulocytic ehrlichiosis has emerged as an important
human health problem since 1990. This disease was first identified
in Wisconsin and Minnesota, but is now recognized across wider
areas of the country (particularly in the northeastern and midwestern
U.S.). Case fatality rates range from 0.7-4.9%.
- Patients present initially with vague signs of fever (sometimes
fever-of-unknown-origin is the only presenting symptom) and headache,
but can develop muscle aches, nausea, cough, leukopenia and thrombocytopenia.
- Clinically, HME and HGE can be quite similar in appearances.
In addition, both clinical presentations can overlap that of
Lyme disease.
- Recent evidence indicates that, as in E. canis-infected
dogs, anti-platelet antibodies may contribute to the thrombocytopenia
that typifies acute HGE.
- In endemic areas, such as northwestern Wisconsin, nearly
15% of people are seropositive for HGE, despite never having
had symptoms consistent with infection. Thus, many infections
may be subclinical. Conversely, some patients suffer recurrent
fevers, chills and fatigue after treatment, apparently in the
absence of persistent infection.
Genetic sequencing data indicate that the causative agent
of HGE is very closely related to Ehrlichia equi and Anaplasma
phagocytophila, which causes granulocytic ehrlichiosis in
both animals and people in Europe, Asia and Africa. Thus, all
3 of these Ehrlichia species are now considered a single
organism, Anaplasma phagocytophila.
- Experimental transfusion of blood from HGE human patients
to horses induced equine ehrlichiosis!
- Not surprisingly, since Ixodes spp. ticks are the
vector for A. phagocytophila and B. burgdorferi,
dual infections have been documented in humans (and in horses).
