New Tests Will Help Detect Fish Virus

ITHACA, N.Y. – A new test will help scientists quickly detect a fast-spreading aquatic virus that threatens the Great Lakes fishing industry, according to its developers at Cornell University.

Current tests for the viral hemorrhagic septicemia virus involve culturing cells and can take up to a month. The new technique, which measures viral genetic material, takes only 24 hours to identify the virus, said Paul Bowser, a Cornell professor of aquatic animal medicine.

“Earlier detection of the virus will provide us with a powerful research and diagnostic tool that will greatly aid in efforts to limit the impact of VHSV,” Bowser said Thursday.

The researchers hope to have the technique validated by the end of 2007.

The virus is relatively common in continental Europe and Japan, where it first affected commercially grown freshwater trout in the 1930s and 1940s. Scientists have said it was likely transported to North America in ballast water from ships.

The virus, which causes internal bleeding in fish but poses no threat to humans, was discovered in the United States in 1988 in Coho and Chinook salmon in the Pacific Northwest. It made its first known appearance in the Great Lakes in 2005, killing freshwater drum and muskellunge.

Since then, the virus has been found in a wide variety of dead fish from the St. Lawrence River, the Niagara River, Lake St. Claire, Lake Erie, Lake Ontario and, most recently, Lake Huron. The virus detected in Lake Huron was only 22 miles from Lake Michigan.

Using a $275,000 grant from New York Sea Grant, Cornell researchers set out to develop a genetics-based test to spot the virus in both tissue and water samples.

“We believe that the test we are developing has the capabilities of detecting the virus when it is present in a sample in very low numbers. We believe that this will allow us to detect the virus in both infected fish tissues and in water,” Bowser said.

“In the latter case, we are interested in water as a potential mechanism for transmission of the virus from an infected fish to a non-infected fish. It is possible that an infected fish may shed VHS into the water,” he said.

The new testing technique also provides an indication of the severity of an infection.

Cornell received more than 1,300 fish samples between May and December last year, and researchers have tested all of them using the new technique, Bowser said. They are about two-thirds of the way through testing the same samples using the classic technique, which relies on cell cultures, to compare results.

Currently, there is no vaccine against the virus, and any measures to control its spread will require monitoring outbreaks and isolating fish so they don’t spread the disease, said Jim Casey, Cornell associate professor of veterinary microbiology and immunology and one of the grant’s lead researchers.

The U.S. Department of Agriculture has issued an order restricting movement of 37 fish species throughout the Great Lakes.

All cases of the virus must be reported to the World Organization of Animal Health. The international agency usually imposes restrictions on any host country with the virus to prevent fish from being moved to other areas and countries.