Pathogenicity study of Equine herpesvirus 1 Infection in balb/c mouse model

Equine Herpes Virus 1 (EHV1) is one of the most ubiquitous viral pathogens of equines causing respiratory symptoms, late-term abortion, neonatal mortality, and neurological disorders. Apart from horses, mice are generally used as an experimental model as it mimics many features of the natural infection. The present study describes the pathological lesions in 3-4 weeks old BALB/c mice infected with 107 PFU of wild EHV1 vRaj strain. Post inoculation, mice showed clinical signs and body weight loss from 1 till 10-11 dpi. Gross examination on detailed necropsy showed changes mostly limited to the respiratory tract. Turbinate and trachea of infected mice showed mild congestion whereas lungs revealed multifocal to coalescing, well demarcated dark red areas at 3 dpi which, by 9 dpi, entered completely into the stage of grey hepatization. By 14 dpi, lungs showed some signs of resolution. Histopathological changes corroborated the gross findings and showed greatest degree of severity at 3 and 5 dpi. Turbinate and tracheal sections revealed severe necrosis and erosion of the epithelium at 3 dpi. However, by 14 dpi, intact epithelium could be appreciated. Lesions in the lungs were mostly characterized by multifocal thickening of the interalveolar septa, proliferation of type II pneumocytes, necrosis and desquamation of bronchial and bronchiolar epithelium with peribronchiolar and perivascular aggregations of mononuclear cells. Moderate to severe necrosis of the interstitium with necrotic neutrophils and syncytial cells were also discernible. However, with each interval the severity decreased and by 14 dpi, signs of resolution could be appreciated with the interalveolar septa returning back to normal with less cellular infiltration. On indirect immunoperoxidase test, strong demonstration of EHV1 antigen in trachea as well as the lungs was observed on 3 dpi. On the other hand, lungs of control mice on gross and histopathological examination were apparently normal.