The intranasal infection of 55 male BALB/c mice with equine herpesvirus type 1 (EHV-1) was used to study the histopathological changes and the distribution of viral antigens by the indirect immunoperoxidase and routine hematoxylin and eosin in the pulmonary tissues compared with 22 control. The animals were sacrificed and necropsied 12, 24 and 36 hours post infection (P.I.), beside 2, 3, 4, 5, 6, 7, 10 and 15 days P.I. The lungs were fixed in neutral buffered formalin. Five microns thick paraffin sections were prepared, stained with immunoperoxidase beside hematoxylin and eosin and examined microscopically.
Specific histopathological lesions were detected in the lung tissues, 24 hours P.I. Necrotic changes and eosinophilic intranuclear inclusion bodies were observed in the linning epithelium of the bronchioles. The maximum number of the inclusion bodies was seen at 2 days P.I. while they were absent at 5 days P.I. Moreover bronchiolitis and adjacent alveolitis beside focal thickening of interalveolar septa together with acute and chronic inflammatory cells were detected, 2 days P.I. The indirect immunoperoxidase technique showed that the majority of EHV-1 antigen positive cells were detected in the bronchiolar epithelium at 36 hours and 2 days P.I. A few antigens were also detected in the alveolar pneumocytes indicating that these cells are also a target for EHV-1. EHV-1 antigen was mainly detected in the nucleus and cytoplasm of the bronchiolar epithelial cells. Some bronchial epithelial cells exhibited a positive reaction on the plasma membrane.
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