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Last Week's Medical Mystery

A 37-year-old previously healthy man presents with a 7 day history of fever  myalgias, fatigue, anorexia, and intermittent headaches, nausea, and diarrhea. You are told that he is anemic with low white blood cell and platelet counts. You are give a Wright-Giemsa stain of his peripheral blood (see below). What is your diagnosis, what test(s) would you order to confirm your suspicions, and what treatment, if any, do you recommend?

blood smear

DIAGNOSES: Monocytotropic ehrlichiosis (HME),  a vector-borne disease transmitted primarily by the lone star tick, which lives as far south as Texas and as far north as New York. The median age of infection is 44 years old, and males are affected 3 times more frequently than females. The prime season for infection is the summer, from May to August. 

Symptoms typically begin within 1-2 weeks of the tick bite, and 75% of patients with HME may need hospitalization. Symptoms range from a simple, nonspecific rash all the way to a septic shock-type picture. Some patients get respiratory failure and require intubation, while others get cardiac or renal failure.  50% of patients have some degree of thrombocytopenia; an absolute neutropenia and/or lymphopenia may also occur. 

During the acute phase of the illness a diagnosis can be made by obtaining a PCR for Ehrlichia chafeensis DNA. Alternately, an ELISA for anti-Ehrlichia chafeensis antibodies can establish the diagnosis if done several weeks into the infection. When ehrlichiosis is suspected, the caregiver should always do a thorough serve of the peripheral smear looking for morula in monocytes (see dark monocyte inclusion in slide above) or granulocytes.   

Treatment is doxycycline 100 mg twice per day for 7-10 days, and treatment is recommended before serologies return. If there is suspected coinfection with Borrelia, then course should be for a full 14 days.  Rifampin is an alternate drug in patients who are allergic or have contraindications to treatment with doxycycline.

Credit: the answer to this medical mystery was provided by Pooja Jagadish, MSIV, ETSU College of Medicine. 


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