Histopathological evolution of experimental paracoccidioidomycosis in Wistar rats

Twenty Wistar rats were inoculated, by the intracardiac route, with 0.5 ml each of a yeast phase suspension of Paracoccidioides brasiliensis Utero strain. The rats were sacrificed at regular intervals post-infection, at which time their lungs, heart, liver, spleen and kidneys were removed, fixed and stained for study. The parameters of interest for the lung specimens were: (a) extent of the lesions; (b) number of fungi; (c) presence of a lymphomononuclear halo. Extrapulmonary lesions were also sought. Until the fourth month post-infection, the lesions were progressive in nature, contained great numbers of viable fungi, and were surrounded by an important lymphomononuclear halo which tended to be confluent. At four and a half months p.i., the extent of the pulmonary lesions was reduced, the granulomas were less compact with fewer viable fungi, macrophages showed microvacuolation, and the lymphomononuclear halo was less pronounced. Extrapulmonary lesions, which were frequently identified in the first months post-infection, diminished from the seventh month onwards. The histological characteristics of extrapulmonary lesions were always the same as those found in the lungs. Infection tended to be controlled by the animals from the fourth month, but without complete resolution of the lesions.