Diagnosis and Management of Human Monocytic Ehrlichiosis (HME) and Human Granulocytic Anaplasmosis (HGA)

Clinical Presentation and Diagnosis

The Centers for Disease Control and Prevention (CDC) recommends considering HME and HGA in patients with fever, headache, and myalgias after outdoor exposure in endemic areas, such as Vermont during fall hiking season 1, 2
The typical incubation period for tickborne rickettsial diseases is 5-10 days, which aligns with the 5-day history of symptoms in this patient 2
The symptom constellation of fever, headache, and myalgias with arthralgias is characteristic of both ehrlichiosis and anaplasmosis, with rash occurring in approximately one-third of adult HME patients 1, 2
The presence of rash does not exclude ehrlichiosis, although it is rare in anaplasmosis 1

A complete blood count may show characteristic leukopenia and thrombocytopenia, present in both HME and HGA 1, 2
A comprehensive metabolic panel may show elevated hepatic transaminases, characteristic of both diseases 1
A peripheral blood smear may show morulae within leukocytes, although this is only visible in 1-20% of cases 1, 5
Acute serology for E. chaffeensis and A. phagocytophilum antibodies may be negative in the acute phase, and PCR testing for E. chaffeensis and A. phagocytophilum DNA from whole blood may be necessary for diagnosis 1, 2, 5

Lyme disease is less likely given the acute febrile presentation without erythema migrans, although coinfection with Borrelia burgdorferi can occur 1, 2
Babesiosis should be considered in patients from Vermont, although it typically presents with more prominent hemolytic anemia 1, 2
Rocky Mountain Spotted Fever (RMSF) is less common in Vermont, and the classic petechial rash typically appears 2-4 days after fever onset 2, 4

The CDC recommends initiating doxycycline 100 mg orally twice daily immediately, without waiting for laboratory confirmation, as treatment should never be delayed while awaiting laboratory results 1, 4
Doxycycline is the treatment of choice for all tickborne rickettsial diseases in adults, and early treatment prevents progression to severe disease and reduces mortality 1, 2, 4
Clinical improvement is expected within 24-48 hours of initiating doxycycline, and convalescent serology should be obtained 2-4 weeks after symptom onset to confirm diagnosis retrospectively 1, 2
Severe complications, including meningoencephalitis, acute respiratory distress syndrome, and multiorgan failure, can occur in immunosuppressed patients, and coinfection with other tickborne pathogens should be considered if clinical response is delayed 1, 8