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May 3, 2011

Seek to develop new nonlethal test for game fish

OSHKOSH -- Four years after the deadly fish disease VHS was first diagnosed in Wisconsin, researchers are returning to the Lake Winnebago system, the site of that discovery, to learn if the virus is still a threat and to develop a faster, cheaper test to detect its presence.

"Our main goal is to develop an antibody test that lets us know whether the VHS virus was present in a fish population, and that won't require any fish to be killed," says Tony Goldberg, a University of Wisconsin-Madison Veterinary School epidemiologist and one of the principal investigators. "That's especially important for valuable and large game fish like musky and walleye."

Goldberg says the researchers also want to learn whether the VHS virus is still active in fish in Lake Winnebago, and to understand when the virus poses the biggest threat to fish.

Such predictive abilities could offer a new way to monitor and manage viral hemorrhagic septicemia throughout all of Wisconsin's waters, and also could be offered to resource managers around the country and world, he says.

Goldberg is working with Sue Marcquenski, fish health specialist for the Department of Natural Resources, Kathy Kurth of the Wisconsin Veterinary Diagnostic Laboratory, and Anna Wilson, a UW-Madison graduate student who previously worked with Marcquenski.

The work, funded by a $200,000 grant from UW Sea Grant, is piggybacking on DNR's spring surveys to collect freshwater drum, which was the first fish species in Wisconsin to suffer a disease outbreak caused by VHS. Drum, a rough fish that also is known as sheepshead, is a good forage item for walleye, sauger, and other game species during their first year of life.

VHS does not affect people nor pets, but can infect 28 species of fish and cause them to bleed to death. Besides Lake Winnebago, VHS also has been detected in a variety of species in Wisconsin's Lake Michigan waters and in lake herring from Wisconsin waters of Lake Superior. DNR's testing thus far has suggested that the disease has not spread to inland waters, but concerns about its future spread remain. VHS was most recently diagnosed in late March 2011 in gizzard shad in shipping canals of the Menomonee River in Milwaukee.

The researchers will be out on the water in coming weeks on the Lake Winnebago system with DNR fish crews. The teams will work together as the DNR conducts annual population assessments.

The VHS researchers will collect blood and organs from about 600 freshwater drum over the next two years. They'll assess those samples for the presence of virus antibodies at two points during a seasonal cycle, in early spring just before VHS has typically been most active, and in fall. The presence of antibodies in the drum will indicate whether the fish were exposed to the virus and survived and subsequently developed an immune response.

By sampling drum before and after the "critical window" for VHS outbreaks, the researchers can examine how the infection status of Lake Winnebago drum changes over the transmission season each year. These data, in combination with the DNR's long-term database on Lake Winnebago drum, will be used to make statistical predictions about when and where VHS is most likely to occur in the future.

Goldberg suspects that the infection may occur in waves, as new fish enter the fishery, or as the immunity wanes in older fish that survived the initial infection. "We think it could be like mumps in humans, with new waves starting as immunity wears off."

Wilson will be working with Kurth, an international expert in animal diagnostic testing, to develop the antibody test as a quicker, cheaper, and non-lethal alternative to current accepted testing methods. Right now, the only way to determine the presence of the VHS virus is by testing internal tissues or fluids from fish which requires killing the fish.

Marcquenski says that the test Kurth and Wilson are developing is also expected to help yield more accurate results regarding the true distribution and prevalence of the virus. The current test can only detect the presence of the virus when it's active. The new test will detect antibodies to the virus, which means the fish were infected at some time in the past and survived the infection.

If fish are tested with both methods, agencies will know if VHS is currently active or was active in the past, she says.

DNR fish biologists who manage Lake Winnebago are eager for the results. Kendall Kamke, senior fish biologist, notes that there have been no obvious effects of VHS on the sheepshead population or on other species in Lake Winnebago.

"There's nothing I could point to and think it might be related to VHS," he says. "But if they can give us a test that will allow us to avoid killing fish and something that could predict the threat level based on XYZ criteria, that would be the silver lining."

FOR MORE INFORMATION CONTACT: Sue Marcquenski, DNR fish health specialist, (608) 266-2871; Tony Goldberg, UW-Madison veterinary epidemiology professor, 608-890-2618 (office); 608-890-3255; Moira Harrington, Wisconsin Sea Grant communications manager, (608) 263-5371; or Kathy Kurth, WVDL virology section chief, (608) 262-5432

Last Revised: Tuesday, May 03, 2011

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