February 2, 2010

Deadly Fish Virus in Upstate N.Y.

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Cornell researchers have confirmed reports that a deadly fish pathogen, viral hemorrhagic septicemia virus, has spread to locations in Lake Superior. First discovered in freshwater fish in Lake Ontario in 2005, this new development means that VHSV has spread to all of the Great Lakes and is posed to threaten the sport fishing industry.

“It is considered by some people to be one of the most serious fish diseases that exists,” said Paul Bowser, professor of aquatic animal medicine at Cornell’s College of Veterinary Medicine. “We have only been dealing with this pathogen in New York state since 2006, so there is a lot we still don’t know about it,” he said.

The largest numbers of fish have died during the spring when fish become stressed with quickly rising water temperatures and efforts to spawn. The disease causes fatal lesions and hemorrhaging among the fish, but poses no threat to humans or any other warm-blooded organism, according to a fact sheet written Bowser.

Bowser and his colleagues at Cornell and the USGS Western Fisheries Research Center collected 874 fish from seven sites in Lake Superior to test for the spread of the virus, and four of them came up positive. The team used a highly sensitive technique developed at Cornell by James Casey, associate professor of microbiology and immunology, that tests for the presence of the viral RNA.

With the geographical spread of the disease in naïve populations of multiple fish species, the virus has become an epidemic that carries immediate consequences for tourism, fish hatcheries, and conservation industries, Bowser said.

VHSV is classified as an World Organization of Animal Health reportable pathogen, which means that it must be reported to international regulatory agencies and may have significant trade implications both domestically and internationally if it continues to spread.

“Sport fishing in freshwater in New York state is 1.4 billion dollars a year. Freshwater fishing in the Great Lakes only is 4.2 billion annually,” said Bowser. “It is a huge economic force.”

People come from all over the United States to fish in the Great Lakes, so the effect of the disease extends to hotels, restaurants, boat rentals and related fishing suppliers.

“It can just be the public perception that a lot of fish are dying that make people choose not to go fishing and vacation elsewhere,” Bowser said.

The best way to manage wild populations of fish is to set up practical surveillance mechanisms to report fish killings, according to Bowser.

The manner by which the infection is transmitted between fish is still unclear, but the transport of contaminated water is one of the main mechanisms of spread, Bowser said. In 2008, the U.S. Department of Agriculture issued an order meant to prevent the movement of infected species among the Great Lakes.

“It is in the Great Lakes, but we just don’t want it to move to other inland bodies of water. To date, it has not been found in any commercial fish farms. There it could potentially become devastating,” Bowser said.

But Bowser emphasized the situation is not devastating yet.

“It is not something you want to panic about. I would say, be on a guarded watch. The sky is not falling, but be on alert,” he said.

The Cornell College of Veterinary Medicine has been examining VHSV for four years. The researchers have worked with the New York Department of Environmental Conservation to determine where the virus is and in which fish it has been found, in both aquaculture and sport-fishing species.

Their efforts also worked toward the development of surveillance mechanisms and a test developed by Casey to confirm positive infections. Bowser and his colleagues in Cornell’s two labs devoted to VHSV will research various ways to decontaminate fish, the differences in susceptibility among species, and strategies to improve surveillance programs that report fish killings and collect fish to study.

Original Author: Brynn Leopold