Morphological aspects of Paracoccidioides brasiliensis in lymph nodes: implications for the prolonged latency of paracoccidioidomycosis?

In order to determine if fungal morphology in tissues would furnish indicat ions on the viability of Paracoccidioides brasiliensis yeast cells, lymph n ode biopsies from five patients with paracoccidioidomycosis, including one with residual circumscribed lesions, were examined. A program that allows t ransferring of microscopic images to the computer for further processing wa s used. In the four active cases, the infected lymph nodes had over 49% of healthy-looking yeast cells while in the case of the residual lesion, this figure was smaller (21%). The residual had a larger proportion of aberrant yeast cells, with predominance of shell-like, empty cells (33%) and crescen t bodies (30%); balloon-like yeasts were also seen (16%). The last two type s of cells were also seen in the active lesions, but in smaller proportions , less than or equal to 8% and less than or equal to 9%, respectively. The number of multiple budding yeast cells, which clearly demonstrate fungal vi ability, ranged 24-33% in active cases but was only 5% in the residual lesi on. Although the number of biopsies examined is small, the results tend to indicate that the morphology of P. brasiliensis yeast cells in walled-off t issues is abnormal and that the number of viable elements is small. There m ight be a connection between these findings and the long latency period ill ustrated by those patients with paracoccidioidomycosis that have been diagn osed in non-endemic areas. Additionally, if P. brasiliensis yeast cells wer e to be subjected to the microaerophilic environment present in walled-off lesions, they would probably require a long time to multiply. Under these c ircumstances, the mycosis would also need many years to manifest.