Doughnut granuloma is a finding of :-

A fibrin ring granuloma also known as doughnut granuloma is a histopathological finding that is characteristic of Q fever. On H & E stain, fibrin ring granuloma consists of a central lipid vacuole surrounded by a dense red fibrin ring and epithelioid macrophages Fibrin ring granulomas may also be seen in Hodgkin's disease and infectious mononucleosis. RMSF (Rocky Mountain Spotted Fever) is caused by Rickettsia rickettsii Lyme disease is caused by Borrelia burgdorferi Human monocytic Ehrlichiosis is caused by E. chaffenensis Human granulocytic Ehrlichiosis is caused by E. phagocytophilum.