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 str ain. 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 lymphomo nonuclear halo. Extrapulmonary lesions were also sought. Until the fourth m onth post-infection, the lesions were progressive in nature, contained grea t numbers of viable fungi, and were surrounded by an important lymphomononu clear halo which tended to be confluent. At four and a half months p.i., th e extent of the pulmonary lesions was reduced, the granulomas were,less com pact with fewer viable fungi, macrophages showed microvacuolation, and the lymphomononuclear halo was less pronounced. Extrapulmonary lesions, which w ere frequently identified in the first months past-infection, diminished fr om the seventh month onwards. The histological characteristics of extrapulm onary lesions were always the same as those found in the lungs. Infection t ended to be controlled by the animals from the fourth month, but without co mplete resolution of the lesions.