Since 2014 we observed a noticeable increase in sudden deaths of green tree pythons (Morelia viridis). A total of 12 affected green tree pythons from 7 different breeders were submitted for a diagnostic post mortem examination. The gross examination revealed accumulation of mucus within airways and lung, associated with enlargement of the entire lung. Histology showed marked hyperplasia of the airway epithelium and faveolar type II pneumocytes. Using next-generation sequencing (NGS) on lung samples of diseased snakes we identified a viral RNA genome that was approximately 85% identical with nidoviruses previously identified in ball pythons and an Indian python. We then confirmed the presence of the novel nidovirus in all diseased snakes by RT-PCR. To attempt virus isolation, we established primary cell cultures of Morelia viridis liver and brain, these were inoculated with lung homogenates of diseased snakes. Ultrastructural examination of concentrated cell culture supernatants revealed nidovirus particles, and subsequent NGS analysis yielded the full genome of the novel Morelia viridis nidovirus (MVNV). We then generated an antibody against MVNV nucleoprotein and MVNV specific oligoprobes and used immunohistology and RNA in situ hybridisation to identify the viral target cells in the lungs. Nidoviruses are a likely cause of severe pneumonia in pythons and cause sudden outbreaks in breeding collections.
Keywords: Nidovirus, pneumonia, Morelia viridis