Dengue, also known as dengue fever, is an infectious disease caused by a virus transmitted by mosquitoes in (sub)tropical areas. The incubation period is 3-14 days, and although most infections are mild, symptoms such as high fever, headache, and muscle aches may occur. However, a small percentage of infections can lead to serious complications, such as dengue hemorrhagic fever and dengue shock syndrome, which can be life-threatening without treatment.

This specimen from a 46-year-old man shows a violent reaction of the lymphocytes. The atypical, plasmacytoid reactive lymphocytes have a deep dark blue cytoplasm, coarse nuclear chromatin and, in part, an aberrant nuclear shape. Differentiating between plasmacytoid and plasma cell is difficult.