Researchers have identified a novel virus 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®, the online open-access journal of the American Society for
Microbiology.
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 senior study author Joseph L. DeRisi, PhD, 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," DeRisi
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), did not arise from people but have been transferred originally from
animals. 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.
To identify a cause of disease, the scientists used
a technique called shotgun metagenomics to sequence RNA of eight of the snakes,
finding 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 that the virus was most prevalent in the sick animals'
respiratory tract tissue, and that the nidovirus is most similar to a subset of
the 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."
Yet to be determined, said study coauthor Mark
Stenglein, PhD, 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. In a previous study published in mBio in August 2012, DeRisi, Stenglein
and colleagues discovered the first reptile arenavirus. The team is continuing
work identifying reptilian viruses. "I think it's the tip of the
iceberg," DeRisi said. Indeed, within the same month, two additional
groups reported identification of a nearly identical virus, in a total of five
additional pythons, all with lung disease.
Citation
Mark D. Stenglein et al. Ball Python Nidovirus: a
Candidate Etiologic Agent for Severe Respiratory Disease in Python regius. mBio, September 2014 DOI:
10.1128/mBio.01484-14