Human granulocytic anaplasmosis acquired in Switzerland: a case report

BACKGROUND: Human granulocytic anaplasmosis, caused by Anaplasma phagocytophilum, is a tick-borne disease endemic in North America that is emerging in Europe and may be underdiagnosed in Switzerland. CASE PRESENTATION: A man in his early seventies receiving methotrexate for ankylosing spondylitis and exposed to ticks presented with a 2-day history of fever, headache and dizziness. Despite empirical broad-spectrum beta-lactam and macrolide therapy, high fever of undetermined origin persisted, and neurological deterioration occurred (somnolence, dysarthria, ataxia, diplopia). Cerebrospinal fluid analysis showed 10 mononuclear cells/µL (normal <5 cells/µL) and protein 476 mg/l (150–450 mg/l). Brain MRI revealed nonspecific leukoencephalopathy. Intravenous doxycycline 100 mg twice daily was empirically initiated on day 7 after symptom onset, resulting in clinical cure within 3 days. Human granulocytic anaplasmosis was retrospectively confirmed by IgG seroconversion against A. phagocytophilum after 6 weeks (8-fold titre increase from <1:64 to 1:512). DISCUSSION: Human granulocytic anaplasmosis represents a diagnostic challenge in non-endemic areas. The human granulocytic anaplasmosis clinical spectrum ranges from mild self-limiting flu-like illness to severe, life-threatening multisystem disease, especially in older immunocompromised patients. Acute-phase diagnosis relies on blood PCR testing. Seroconversion with a 4-fold increase in IgG titre within 2–4 weeks is the gold standard for diagnosis in the convalescent phase. Doxycycline is the first-line antimicrobial therapy. CONCLUSION: Human granulocytic anaplasmosis is an emerging tick-borne disease which can be acquired in Switzerland. Early diagnostic work-up using blood PCR and empirical doxycycline therapy are key in patients at risk of exposure to ticks who present with severe acute febrile illness without an alternative diagnosis.