Experimental infection of carpet pythons (Morelia spilota) with sunshinevirus

Sunshinevirus was originally isolated in 2008 from a collection of Australian pythons suffering an outbreak of neuro-respiratory disease. Sunshinevirus infection cases, including chronic asymptomatic infections, have subsequently been detected throughout Australia by PCR testing. To investigate the association between sunshinevirus infection and disease, controlled experimental infection studies in carpet pythons (Morelia spilota) were undertaken. The study aims were to determine if there was a causal relationship between sunshinevirus and disease, as well as collecting information on potential virus transmission routes, infectious doses, target organs for viral replication and pathology, and incubation period. Between August 2016 and February 2018, six pythons were inoculated with sunshinevirus, two were sham inoculated as control animals, and two were co-housed with infected animals. All animals were sampled weekly and sunshinevirus was detected in virus-inoculated animals by PCR 6-14 days post-inoculation. Five of the six virus-inoculated carpet pythons developed neuro-respiratory disease, and sunshinevirus could be re-isolated from liver and kidney tissues as well as blood. One of the co-housed pythons became infected, consistent with natural transmission. The other co-housed python remained uninfected. Clinical signs commenced 3-7 months after viral exposure. They were slow to develop, often subtle, and predominantly neurological. Histologically, there was a non-suppurative encephalomyelitis, with the most consistent finding being vacuolation and gliosis in the brain. Cytoplasmic inclusions were found in a range of predominantly epithelial tissues. Infected pythons shed infectious virus 2.5-7 months before they showed obvious clinical signs of disease and remained viremic (for several months) until euthanasia.

Australian pythons are extensively kept in captivity. Since the 1990s, native Australian snakes with neuro-respiratory signs of disease, sometimes fatal, had been presenting to veterinarians in Australia. Research conducted at Murdoch University on some of these snakes resulted in the discovery of a novel virus, now named sunshinevirus (Sunviridae). Widespread follow-up PCR testing of pythons throughout Australia linked sunshinevirus infection to both asymptomatic virus-carriers and pythons showing signs of disease. Experimental infections were conducted to determine whether sunshinevirus infection caused disease in Australian pythons. The experiments demonstrated a causal relationship by fulfilling Koch's postulates, and 5/6 infected animals developed neurological disease. Infected pythons shed virus persistently for months, but control animals remained uninfected. Our findings provide veterinarians with valuable information for the management of sunshinevirus in zoos and private collections.