Chronic pulmonary and disseminated paracoccidioidomycosis in mice: quantitation of progression and chronicity.

An animal model of chronic paracoccidioidomycosis was established in male adult BALB/cByJIMR mice by intranasal instillation of different doses of yeast form Paracoccidioides brasiliensis. The inoculum was standardized in terms of virulence, age of the culture, percentage of multicellular fungal units containing 1-3 cells, and viability. Progression and chronicity of the infection was measured by quantitative counts of colony forming units (CFU) of P. brasiliensis from infected lungs, spleens, and livers in a newly developed culture medium. The body weight of the mice and the organ weights were also used to monitor the disease process. Infection with several challenge sizes progressed in the lungs until a maximum of 10(7)-10(8) CFU per lung was reached; in general, the higher the inoculum, the sooner this maximum was reached. In mice infected with 2.5 X 10(6) CFU the maximum was reached at 8 weeks, whereas in mice infected with 3 X 10(4) CFU the maximum was reached 14 weeks after infection. Dissemination of the disease progressed until there were 10(6)-10(7) CFU per spleen or liver. The higher the infective dose, the shorter the time required to reach a maximum stable population of yeasts in spleen and liver (12 weeks with inoculum of 2.5 X 10(6) CFU, 18-26 weeks with inoculum of 7.0 X 10(3) CFU). The body weight of mice tended to diminish with time after infection compared to uninfected controls. In contrast, the weight of lung and spleen increased with time after infection. This model of chronic paracoccidioidomycosis permits evaluation of progression of the disease process and of the multiplication of the yeast in organs.