Divergent Bornaviruses from Australian Carpet Pythons with Neurological Disease; Date the Origin of Extant Bornaviridae Prior to the End-Cretaceous Extinction
2018 Joint EAZWV/AAZV/Leibniz-IZW Conference
Timothy H. Hyndman1, BSc, BVMS, PhD, MANZCVS (Veterinary Pharmacology); Catherine M. Shilton2, BSc, DVM, DVSc; Mark D. Stenglein3, PhD; James F.X. Wellehan, Jr.4, DVM, PhD, DACZM, DACVM (Virology, Bacteriology/Mycology)
1College of Veterinary Medicine, School of Veterinary and Life Sciences, Murdoch University, Perth, WA, Australia; 2Berrimah Veterinary Laboratories, Department of Primary Industry and Resources, Northern Territory Government, Berrimah, NT, Australia; 3Department of Microbiology, Immunology, and Pathology, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO, USA; 4Department of Comparative, Diagnostic, and Population Medicine, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
Tissues from Australian carpet pythons (Morelia spilota) with neurological disease and non-suppurative encephalitis were screened for viruses using next-generation sequencing. Coding complete genomes of two viruses in the family Bornaviridae were identified, divergent at a level constituting a new bornaviral genus, Carbovirus. These viruses had a transposition of the G and M genes compared to previously known bornaviruses and other viruses in the order Mononegavirales (paramyxoviruses, filoviruses, and rhabdoviruses). Knowledge of these viruses enabled recognition of further endogenous bornavirus-like elements (EBLs) in diverse placental mammal genomes, including humans. Codivergence patterns and shared sites revealed integrations into host genomes of viruses resembling these novel python bornaviruses prior to the end-Cretaceous (K-Pg) extinction, 66 MYA. There is strong evidence that climate warming played a significant role in the K-Pg extinction.4 Given the physiological disadvantages mammals have with water conservation, and the previous result of the end-Permian climate warming, it is unexpected that mammals would dominate over reptiles following a K-Pg climate warming event.1,2 An EBL similar to the previously known bornaviruses protects thirteen-lined ground squirrels against infection with the previously known bornaviruses.3 It is possible that EBLs protected mammals from ancient carboviral disease, providing a selective advantage to them in the recovery from the K-Pg extinction. A degenerate PCR primer set was developed to detect a highly conserved region of the bornaviral polymerase gene. It was used to detect 15 more genetically distinct carboviruses from Australian pythons.
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