FIG 4.

Histopathological and immunohistochemical findings in tissues from animals infected intraperitoneally with Rickettsia rickettsii. Testes stained with hematoxylin and eosin showing lymphohistiocytic vasculitis of the tunics and interstitium (A and B). Immunohistochemical staining showing focal to extensive rickettsial antigens (red) in Costa Rica-infected testes (C). Capillaritis with fibrin thrombus in the lung of a Gila-infected animal (D). Mild vacuolar degeneration, rare single-cell necrosis, and mild lobular inflammation, comprising the predominant hepatic lesions produced following infection with all isolates except Iowa (E). Spleen histiocytes forming loose granulomas in a Sawtooth-infected animal (F). Magnifications, ×50 (A, B, and E), ×100 (C and D), and ×25 (F).