Effect of immunosuppression on the pathogenesis of respiratory zygomycosis in rabbits intranasally infected with Absidia corymbifera

The study was envisaged for elucidating the effect of immunosuppression on the pathology and pathogenesis of experimental respiratory absidiomycosis in rabbits. Seventy rabbits used in the experiment were divided into different groups viz. non-immunosuppressed, immunosuppressed with cyclophosphamide and immunosuppressed with methylprednisolone respectively, and a control group. The experiment was continued for 50 days during which all the infected animals exhibited clinical signs of respiratory distress but no mortality. The infected rabbits showed gross lesions mainly in the form of pneumonic consolidations in the lungs in antero-ventral lobes initially followed by spread to the other lobes. Similarly, microscopic lesions were restricted to lungs and consisted of early pyogranulomas dominated by fungal invasion and spread, followed by chronic granulomatous reaction and a recovery during the later stages. Fungus was demonstrated and re-isolated only from lung lesions up to 15 days postinfection (DPI) in non-immuno-suppressed group and up to 30 DPI in both the immunosuppressed groups suggesting no systemic dissemination. The findings of the present study indicated that immunosuppression increased the extent, duration and severity of the pathological lesions associated with absidiomycosis in the lungs. Moreover, an assessment based on gross and histopathological lesions revealed cyclophosphamide to be a more potent immunosuppressant than methylprednisolone.