In 2014 we observed a noticeable increase in sudden deaths of green tree pythons (). Pathological examination revealed accumulation of mucoid material within airways and lung, associated with enlargement of the entire lung. We performed full necropsy and histological examination on 12 affected green tree pythons from 7 different breeders to characterise the pathogenesis of this "mucinous" pneumonia. By histology we could show a marked hyperplasia of the airway epithelium and of faveolar type II pneumocytes. Since routine microbiological tests failed to identify a causative agent, we studied lung samples of a few diseased snakes by next-generation sequencing (NGS). From the NGS data we could assemble a piece of RNA genome <85% identical to nidoviruses previously identified in ball pythons and Indian pythons. We then employed RT-PCR to demonstrate the presence of the novel nidovirus in all diseased snakes. To attempt virus isolation, we established primary cell cultures of liver and brain, which we inoculated with lung homogenates of infected individuals. Ultrastructural examination of concentrated cell culture supernatants showed the presence of nidovirus particles, and subsequent NGS analysis yielded the full genome of the novel virus, Morelia viridis nidovirus (MVNV). We then generated an antibody against MVNV nucleoprotein, which we used alongside RNA hybridisation to demonstrate viral antigen and RNA in the affected lungs. This suggests that in natural infection MVNV damages the respiratory tract epithelium which then results in epithelial hyperplasia, most likely as an exaggerated regenerative attempt in association with increased epithelial turnover. Fairly recently novel nidoviruses associated with severe respiratory disease were identified in ball pythons and Indian pythons. Herein we report isolation and identification of a further nidovirus from green tree pythons () with fatal pneumonia. We thoroughly characterize the pathological changes in the infected individuals, and show that nidovirus infection is associated with marked epithelial proliferation in the respiratory tract. We speculate that this and the associated excess mucus production can lead to the animals' death, by inhibitingthe normal gas exchange in the lung. The virus was predominantly detected in the respiratory tract, which renders transmission via the respiratory route likely. Nidoviruses cause sudden outbreaks with high mortality in breeding collections, most affected snakes die without prior clinical signs. These findings, together with those of other groups, indicate that nidoviruses are a likely cause of severe pneumonia in pythons.

Boid inclusion body disease (BIBD) is an often fatal disease affecting mainly constrictor snakes. BIBD has been associated with infection, and more recently with coinfection, by various reptarenavirus species (family Arenaviridae). Thus far BIBD has only been reported in captive snakes, and neither the incubation period nor the route of transmission are known. Herein we provide strong evidence that co-infecting reptarenavirus species can be vertically transmitted in Boa constrictor. In total we examined five B. constrictor clutches with offspring ranging in age from embryos over perinatal abortions to juveniles. The mother and/or father of each clutch were initially diagnosed with BIBD and/or reptarenavirus infection by detection of the pathognomonic inclusion bodies (IB) and/or reptarenaviral RNA. By applying next-generation sequencing and de novo sequence assembly we determined the “reptarenavirome” of each clutch, yielding several nearly complete L and S segments of multiple reptarenaviruses. We further confirmed vertical transmission of the co-infecting reptarenaviruses by species-specific RT-PCR from samples of parental animals and offspring. Curiously, not all offspring obtained the full parental “reptarenavirome”. We extended our findings by an in vitro approach; cell cultures derived from embryonal samples rapidly developed IB and promoted replication of some or all parental viruses. In the tissues of embryos and perinatal abortions, viral antigen was sometimes detected, but IB were consistently seen only in the juvenile snakes from the age of 2 mo onwards. In addition to demonstrating vertical transmission of multiple species, our results also indicate that reptarenavirus infection induces BIBD over time in the offspring.

In December 2019, a novel coronavirus of likely zoonotic origin, SARS-CoV-2, was discovered following detection of an outbreak of acute respiratory disease in people from Wuhan, China (Zhou et al., 2020). The virus has since spread across the world and in early March 2020 the WHO declared COVID-19, the disease caused by the virus, a pandemic (https://www.who.int/dg/speec hes/detai l/who-direc tor-gener al-s-openi ng-remar ks-at-the-media -brief ing-on-covid -19---11-march -2020). As of November 2020, worldwide mortality from COVID-19 was over 1,360,000 deaths (https://coron avirus.jhu.edu/map.html; Accessed November 20, 2020).Coronaviruses have large (~30 kb), positive-sense, RNA genomes and are known to infect a variety of mammals and birds. Their genomes are also known to have a high propensity for recombination with other coronaviruses. Coronaviruses are classified as alpha-, beta-, gamma-or deltacoronaviruses. Both alpha-and betacoronaviruses infect mammals, and while worldwide bats are known to be infected by both types of viruses (Decaro & Larusso, 2020; Falcon et al., 2011), only alphacoronaviruses have been found to date in North American bats (Olival et al., 2020).