Severe Secondary Haemophagocytic Lymphohistiocytosis Syndrome Due to Crimean-Congo Haemorrhagic Fever Virus: Thinking out of the Box.

Introduction: Crimean-Congo haemorrhagic fever is an acute, often severe haemorrhagic disease caused by the homonymous virus. On the other hand, severe life-threatening secondary haemophagocytic lymphohistiocytosis is a rare entity usually associated with underlying haematological malignancies, infectious or autoimmune diseases. Herein, we report a fatal case of severe secondary haemophagocytic lymphohistiocytosis due to the abovementioned virus but also a second case of Crimean-Congo haemorrhagic fever with virus-induced threatening haemophagocytic lymphohistiocytosis in an internist who was responsible for the patient's management. Case description: A 72-year-old stockbreeder progressed to fatal secondary haemophagocytic lymphohistiocytosis due to Crimean-Congo haemorrhagic fever virus (fever, hepatosplenomegaly, severe cytopenias, low fibrinogen, hypertriglyceridemia and extremely high ferritin levels), despite aggressive supportive measures and specific treatment with corticosteroids and intravenous γ-immunoglobulin. The second case was a 54-year-old internist who acquired the Crimean-Congo haemorrhagic fever virus through mucocutaneous exposure to the patient's blood, recovering fully with prompt double treatment against active viral replication and early stage haemophagocytic lymphohistiocytosis. Discussion: Crimean-Congo haemorrhagic fever virus is a rare cause of secondary haemophagocytic lymphohistiocytosis with an unfavourable outcome if the patient has a rapidly progressing course as in our first case. Clinicians should maintain a high level of clinical suspicion in the appropriate clinical setting since prompt initiation of treatment for secondary haemophagocytic lymphohistiocytosis as in the second case, can be lifesaving. Conclusion: These cases emphasize that Crimean-Congo haemorrhagic fever virus can be a cause of severe life-threatening haemophagocytic lymphohistiocytosis even in non-endemic areas, while stringent infection control to prevent secondary healthcare-associated transmission is of the utmost importance. LEARNING POINTS: Crimean-Congo haemorrhagic fever virus can be a rare cause of severe life-threatening haemophagocytic lymphohistiocytosis syndrome even in non-endemic areasClinical suspicion for haemophagocytic lymphohistiocytosis due to Crimean-Congo haemorrhagic fever virus should be high in the appropriate clinical setting as prompt initiation of therapy can be lifesavingIt is important to apply secondary prevention of healthcare-associated transmission of Crimean-Congo haemorrhagic fever.