When Joseph DeRisi and colleagues published a paper in mBio two years ago identifying the first arenavirus in reptiles, it highlighted to him the need to look more broadly across veterinary species when searching for pathogens. Not only was the newly identified virus responsible for the development of a snake illness called inclusion body disease, which leads to severe digestion troubles and neurologic symptoms, but it also was related to Ebola virus.
Their continuing studies in snakes have led to the identification of another novel virus in snakes, one that could be the source of a severe, sometimes fatal respiratory disease that has been observed in captive ball pythons since the 1990s. The work is published this week in mBio.
Investigators observed the virus, which they named ball python nidovirus, in eight snakes with pneumonia; virus levels were highest in the animals’ lungs and other respiratory tract tissues. The team also sequenced the genome of the virus, finding it to be the largest of any RNA virus yet described.
Ball pythons have become one of the most popular types of reptiles sold and kept as pets, the authors said, because of their relatively modest size, docile behavior and ease of care. Respiratory disease has been noted in these animals since the 1990s but until now a potential cause has not been identified, said DeRisi, chair of the Department of Biochemistry and Biophysics at the University of California, San Francisco, in part because of the limitations of available technology.
“This is really exciting because up to this point there have been no known viruses of this type in reptiles,” he said. “Some of the most feared diseases we know of, like Ebola virus, HIV, Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS), these are zoonotically transferred. They’re not coming from people to people originally. Our work suggests there may be very large reservoirs of genetic diversity of viral families that can cause human disease in under studied organisms, like reptiles. We would do well to look broadly across all species.”
DeRisi and colleagues at seven other institutions across the country studied tissue samples from ball pythons with symptoms of respiratory disease from seven collections in Florida, Oklahoma, Pennsylvania, Texas and Wisconsin. Autopsies on the animals found lesions in the animals’ upper and lower respiratory tracts, and additional lesions in other areas of the body. Using an electron microscope, investigators observed virus-like particles in the cells lining the lungs of two snakes.
Using shotgun metagenomics to sequence RNA of eight of the snakes, they found a novel nidovirus in all of them, but not in a search of tissues from 57 other snakes not affected by pneumonia, collected for other studies. Additional work found the virus was most prevalent in the sick animals’ respiratory tract tissue, and that the nidovirus is most similar to a subset of nidoviruses called toroviruses, which infect mammals and ray-finned fish.
“The identification of a novel nidovirus in reptiles contributes to our understanding of the biology and evolution of related viruses, and its association with lung disease in pythons is a promising step toward elucidating an etiology for this long-standing veterinary disease,” DeRisi said. “Our report will enable diagnostics that will assist in determining the role of this virus in the causation of disease, which would allow control of the disease in zoos and private collections.”
Within the past month, two other research groups published papers finding a nearly identical virus in pythons with lung disease, though one study featured a single snake, and the other had four. “The good news is they all found this virus in association with pneumonia, which strengthens the relationship between the virus and the causation of the disease,” DeRisi said.
Yet to be determined, said study coauthor Mark Stenglein, is how the virus is spread, whether ball pythons are the primary natural host for the virus, and how widespread the virus is in the wild. The team is continuing work identifying reptilian viruses. “I think it’s the tip of the iceberg,” DeRisi said.
-- Karen Blum