Amphibians, the big-eyed, swimming-crawling-jumping-climbing group of water and land animals that includes frogs, toads and salamanders, are the most endangered vertebrates in the world. Now, these charismatic creatures could face a new foe: Spring viraemia of carp virus, or SVCV, a fish disease not previously known to infect amphibians.
U.S. Geological Survey scientists recently identified SVCV in Chinese firebelly newts (Cynops orientalis), a type of salamander, which were imported to the United States through the international pet trade. This critical discovery marks the first time that SVCV has been detected in a group of animals other than fish, and may present a further threat to already-declining global populations of amphibians.
“The U.S. has the highest diversity of salamanders in the world,” said Jonathan Sleeman, director of the USGS National Wildlife Health Center, or NWHC. “Although the susceptibility of amphibians to SVCV is currently unknown, novel introductions of this pathogen into the U.S. could have economic and biological impacts.”
Spring Viraemia of…What?
SVCV is a known fish virus that presents an economic threat to the commercial aquaculture industry. It causes illness and death in carp, koi and other commercially important fish species.
Although SVCV probably isn’t native to North America, it has been identified in dead wild and captive fish in the U.S. on at least nine occasions. There have likely been three separate introductions of SVCV to North America, but how the virus may have spread once introduced is unclear. It was first detected in the U.S. in 2002 at the farm of a koi and goldfish breeder in Virginia, and in wild carp at a public lake in Wisconsin. It has since been found in Illinois, Minnesota, Missouri, Minnesota and Washington.
The Salamander Story
In August 2015, scientists from the USGS NWHC tested 11 Chinese firebelly newts that died in a larger shipment of live newts. The animals were legally imported to the U.S. from China.
Acting as wildlife disease detectives investigating the cause of death, USGS scientists screened the carcasses for the Batrachochytrium salamandrivorans, or Bsal, fungus – the cause of a different emerging salamander disease that has led to die-offs of wild salamander populations in Europe. Bsal likely originated in Asia and spread to wild European populations through the import and export of salamanders. Previous USGS research suggests that although Bsal has not yet been found in wild U.S. salamanders, it is likely to emerge in the U.S. through importation of animals by international pet traders or other human activities.
The newts tested negative for Bsal. However, the scientists instead detected SVCV in all 11 carcasses – a surprising discovery. The USGS researchers recently published a report documenting their finding in the journal Emerging Microbes and Infections.
“Our discovery of SVCV in these salamanders was unexpected,” said Hon Ip, a USGS NWHC scientist and the lead author of the report. “The discovery indicates that internationally traded amphibians can potentially contribute to the global spread of emerging fish and wildlife viruses.”
Through genetic analysis of the carcasses, the USGS researchers confirmed that the newts likely originated near Hangzhou, China. Hangzhou borders Shanghai, where the most closely related SVCV strain was previously identified.
“Early detection of pathogens is critical for preventing outbreaks of infectious disease in humans, livestock and wildlife throughout the world,” said David Blehert, a USGS NWHC scientist and coauthor of the report. “Early detection allows for rapid implementation of management actions to prevent and control the spread of infectious diseases.”
Still, the discovery of SVCV in amphibians raises numerous scientific and policy-related questions that have yet to be tackled. For the USGS disease detectives, this noteworthy finding marks the beginning of a scientific journey that has only begun to unfold.
For more information about wildlife disease research in the U.S., please visit the USGS NWHC website.
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