Clinical Pearls & Morning Reports
Published March 23, 2022
Anaplasmosis, which is caused by the bacterium Anaplasma phagocytophilum, typically leads to hepatitis, thrombocytopenia, and fever. Read the NEJM Case Records of the Massachusetts General Hospital here.
Q: Where in the United States is anaplasmosis most common?
A: Anaplasmosis is a zoonotic infection. The pathogen is transmitted primarily through a bite from the Ixodes scapularis or I. pacificus tick. The geographic distribution of the infection follows that of its vectors, with cases predominantly occurring in the Northeast, Midwest, and Pacific Northwest regions of the United States and southern Canada. The incidence typically peaks in the summer months, when ticks are most active.
Q: Name some of the common clinical and laboratory features of anaplasmosis.
A: In patients with anaplasmosis, the spectrum of illness ranges from asymptomatic infection to severe disease that requires intensive care. Most patients present with fevers, headaches, and myalgias; cough has also been reported. Common laboratory abnormalities include leukopenia, thrombocytopenia, and elevated aminotransferase levels.
A: The diagnosis is often made with the use of nucleic acid amplification testing of the blood, because this test has higher sensitivity and specificity than other methods during acute infection. Serologic testing is also available but is most useful for confirming recent infection during convalescence, since it has lower sensitivity during early infection. Identification of morulae in neutrophils on a peripheral-blood smear is also diagnostic of anaplasmosis; however, the microscopist must have the expertise to accurately differentiate these structures from other intracytoplasmic elements within cells. Given these technical requirements, diagnosis through examination of a peripheral-blood smear is not routinely performed in most clinical laboratories.
A: Doxycycline remains the first-line treatment for anaplasmosis, with treatment courses ranging from 7 to 10 days. Rifampin has also been used successfully as alternative therapy when tetracycline antibiotic agents are contraindicated. Symptoms typically resolve within 24 to 48 hours after the initiation of antibiotic therapy; chronic infection is not known to occur.