After the rickettsia bacteria infects humans through a tick<unk> , it invades endothelial cells in the circulatory system (veins, arteries, capillaries). The body then releases chemicals that cause inflammation, resulting in the characteristic symptoms like headache and fever. The hallmark of all rickettsial diseases is a histology (cellular) finding called lymphohistiocytic vasculitis that involves immune cell deposition into the endothelial cells that make up vessels. This occurs secondary to the chemicals mentioned above, as well as damage from the infection, and involves signals to immune cells (T cells and macrophages) to come to the site of the infection. Rickettsia bacteria species like R.<unk>  replicate around the area of the initial tick<unk> , causing necrosis (cell death) and lymph node inflammation. This is the cause of the characteristic eschar.
African tick bite fever
American tick bite fever
Rat-bite fever
Spondweni fever
Scabies
Colorado tick fever
Sandfly fever
Pacific Coast tick fever