الفهرس 
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Abstract
A Comparative study was done to differentiate the pathogenicity and the histopathological lesions in laboratory animals (the guinea pigs and mice) either male or female infected with either the field isolate or the standard strain of Cr. neoformans. Also a comparison was done to differentiate the lesions by the different routes of infection. Seventy adult male and female guinea pigs and seventy adult male and female mice were used. The dose of injection was 2 X 107 CFU/ml. Four animals from each inoculated group and two untreated control animals were slaughtered every 10 days till the end of the experiment. All animals were observed during the experiment to detect any clinical signs. At the time of slaughter the animals were subjected to postmortem examination to detect any abnormal gross changes. Tissue specimen from brain, lung, liver, spleen and kidney were collected for the histopathological examination, reisolation of Cr. neoformans and estimation of macrophage phagocytic activity (alveolar macrophage in guinea pigs, peritoneal macrophage in mice). The alveolar macrophages in guinea pigs and the peritoneal macrophages in mice were able to engulf the yeast. In guinea pigs, there were no clinical signs observed in all groups all over the experiment. The most prominent postmortem lesions were congestion of the brain meninges and the lung showed diffuse pneumonia. The I/N inoculation in guinea pigs lead to severe granulomatous pneumonia with systemic dissemination of the infection. In mice, there were no clinical signs observed in the mice inoculated intraperitoneal. While in the mice inoculated intradermal there were cutaneous lesions.The most prominent postmortem lesions were multiple granulomes in the lung with severe pneumonia, spleen and liver showed mucoid nodules on their surfaces. The cutaneous lesions appeared as elevated, roughened, hairless plaques. The lesions either after infection with the field isolate or the standard strain were nearly the same but those of the field isolate were more severe. The sex (either male or female) played no role.