Objective. — To evaluate the relationship between elastase activity of different Aspergillus fumigatus (A. fumigatus) isolates and their pathogenicity in mice. Material and methods. — The animals were intravenously (IV) infected with 1  106 conidia/ mouse. The elastase activity in mice sera and survival time were determined. All animals were sacrified at the end of the fourth week, and autopsies were performed for histopathological examination. The tissue sections were stained with Periodic Acid Schiff (PAS) and Verhoeff’s techniques. Results. — The highest elastase activity was associated with the sera of infected mice with elastase-producing A. fumigatus AIR78 as standard strain (0.18  0.02 mm), followed by infected animals with elastase-producing isolates (0.16  0.02 mm) and control mice (0.14  0.02 mm). The elastase activity index (EAI) was determined in value of 0.92  0.27. The survival times in mice infected with elastase-producing isolate and in control group were 21.6 and 30 days, respectively. Histopathological studies showed that the heart and kidneys were more infected by Aspergillus hyphae than other tissues. Conclusion. — It was concluded that there is a significant relationship between elastase activity and survival time in mice with aspergillosis.

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