Comparative lung pathology of equine herpes virus 1 and equine influenza infection in BALB/c mouse model

Amongst all the equine viral diseases, Equine herpesvirus 1 (EHV-1) and Equine influenza virus (EIV) are two OIE listed and most important viral respiratory pathogens of equines. EHV 1 is responsible for causing respiratory symptoms, late-term abortion, neonatal mortality, and neurological disorders, while EIV induces flu-like symptoms in horses showing serous to mucous discharge from nostrils, serous ocular discharge, fever and restlessness. Apart from horses, mice are generally used as an experimental model for EIV and EHV studies. Therefore, to compare the differential pathological lesions of both diseases, the present study describes the pathological lesions in 3-4 weeks old BALB/c mice infected with 107 PFU (25 μl) of wild vRaj (Rajasthan-98), 25 μl of 5×107.2 EID, EIV and PBS respectively. Gross examination on detailed necropsy of lungs revealed multifocal to coalescing, dark red areas at 3 dpi which by 9 dpi entered completely into the stage of grey hepatization (multifocal areas) in EHV1 infection whereas, in EIV infected lungs revealed diffused changes of red hepatization at 3 dpi which proceeded into grey hepatization on 5 dpi. By 14 dpi, lungs showed signs of resolution in both the cases characterized by mild demarcated multifocal grey hepatization areas in EHV1 and diffused grey hepatization areas in EIV infected lungs. Histopathological changes showed the greatest degree of severity at 3 and 5 dpi in both infections. EIV infected lungs revealed moderate to severe necrosis (epithelial cell death) and desquamation of bronchial epithelium at 3 dpi, whereas EHV1 infected lungs showed ballooning of cells with hyperplasia and necrosis followed by desquamation of the bronchial epithelium. EHV1 infected lungs revealed moderate to severe necrosis of the interstitium with infiltration of neutrophils, lymphocytes, macrophages and presence of syncytial formation by coalescing macrophages. The interstitium in EIV infected lungs revealed more lymphocytic infiltration. In addition to all the differences, lungs infected with EHV1 typically revealed the presence of eosinophilic intranuclear inclusion bodies in the lung parenchyma on special staining (Lendrum’s). On the contrary, the lungs of control mice on gross and histopathological examination were normal. The analysis portrays the differences between the gross and histopathology of both the infections for future studies and references.