A case report in cmaj from eastern Ontario highlights how laboratory findings and early molecular testing helped diagnose tick-borne anaplasmosis in a patient who developed the rare complication of acute myocarditis. The report emphasizes that Anaplasma phagocytophilum infection should be considered in patients with unexplained febrile illness, cytopenias, and elevated liver enzymes in endemic regions, even when no tick bite is reported.
Researchers described the case of a 79-year-old man who presented with two days of fatigue, chills, weakness, and a fall. Initial laboratory testing revealed lymphopenia, thrombocytopenia, acute kidney injury, elevated alanine aminotransferase, and increased C-reactive protein. Despite empiric ceftriaxone, his condition worsened, prompting clinicians to broaden the differential diagnosis to include tick-borne infections because of his residence and frequent work in wooded areas.
Diagnostic testing proved pivotal. A peripheral blood smear demonstrated intracytoplasmic morulae within neutrophils, providing an early clue to anaplasmosis, and polymerase chain reaction (PCR) testing subsequently confirmed A phagocytophilum. Testing for babesiosis was negative.
The patient later developed hypoxia and evidence of cardiac involvement. Elevated troponin and B-type natriuretic peptide concentrations, together with echocardiography and cardiac magnetic resonance imaging, confirmed acute myocarditis with reduced left ventricular function. Following treatment with doxycycline, his clinical condition and laboratory abnormalities improved rapidly, and cardiac function had returned to normal at 4-month follow-up.
The researchers noted that anaplasmosis is the second most common tick-borne disease in Canada and that its incidence is increasing as the range of the blacklegged tick expands. Although patients typically present with nonspecific symptoms such as fever, malaise, headache, and gastrointestinal complaints, laboratory abnormalities – including thrombocytopenia, lymphopenia, elevated transaminases, and increased creatinine – may provide important diagnostic clues. Severe complications such as myocarditis, acute kidney injury, respiratory failure, and central nervous system involvement are uncommon but occur more frequently in older or immunocompromised patients and in those with delayed diagnosis.
The report reinforces the value of recognizing characteristic hematologic findings and selecting appropriate confirmatory testing. Peripheral blood smear can provide a rapid presumptive diagnosis when neutrophil morulae are identified, while PCR is the preferred test during the early phase of illness because of its high sensitivity and specificity. Serology is primarily used to retrospectively confirm infection.
The researchers concluded that anaplasmosis should remain part of the differential diagnosis for patients with unexplained febrile illness and compatible laboratory abnormalities in areas where tick-borne diseases are emerging. Prompt laboratory recognition and early doxycycline treatment may help prevent progression to serious complications.
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