DNR Reports Fish Virus Now Found in Lake Huron

An aquatic virus that has been predicted to infiltrate the entire Great Lakes system has reached the waters of Lake Huron as far north as Cheboygan, where, researchers learned last week, it has been present since at least 2005. Re-testing stored fish samples collected in 2005, fisheries officials have learned a fish disease called viral hemorrhagic septicemia (VHS) has spread in Lake Huron, infecting whitefish, walleye, and Chinook salmon, the Department of Natural Resources (DNR) announced Thursday, January 25. Recent analyses of fish sampled from northern Lake Huron have confirmed the existence of the virus in the Cheboygan area, in lake whitefish and walleye samples from the Thunder Bay area, and in Chinook salmon samples from the Swan River egg-take station near Rogers City.

VHS causes disease in fish but does not pose any threat to public health. It was detected for the first time in 2005 in Great Lakes fish species in the U.S. and Canada, and fisheries officials have predicted it will eventually infiltrate the entire Great Lakes system, threatening the fishing industry. It is not known how VHS was transferred to the Great Lakes region or how long it has been in the waterways of the Great Lakes, the DNR reported. Many biologists believe it reached the Great Lakes in the ballast water of ocean freighters.

The U.S. Department of Agriculture banned interstate fish shipments from the Great Lakes last fall, in an emergency measure to keep the virus from spreading, but modified the order after protest from the fish industry that pointed out Great Lakes fish are already being tested for VHS. The modified order allows properly documented fish shipments.

"The continuing march of VHS through the waters of the Great Lakes is a major challenge to our agency and our management options," said DNR Director Rebecca Humphries. "These new discoveries are extremely unfortunate and further highlight the problems created by the constant introductions of new diseases from outside of the Great Lakes region, the speed with which they can spread, and the threat that such pathogens pose to our natural resources."

DNR officials have been in contact with the U.S. Department of Agriculture's Animal and Plant Health Inspection Services, alerting them to the new confirmations of VHS in Lake Huron fish. Fisheries officials are now working to outline steps to slow the spread of the virus, and no immediate policy changes have been announced on the federal level.

VHS was detected in lake whitefish from the Cheboygan area after re-analyzing samples collected in 2005 during a survey for bacterial kidney disease (BKD).

"It is not unusual for us to collect fish that have unknown viruses, which typically require a significant effort to properly identify," said Gary Whelan, fish production manager for the DNR. "Once we had indications of VHS in other samples of fish from Lake Huron, this sample was retrieved from storage and fully analyzed by Dr. Mohamed Faisal at Michigan State University."

Samples from the Thunder Bay area were collected last fall during a mortality event that included lake whitefish and walleyes.

"At the time, we suspected that the cause of the mortality might be related to VHS," said Kelley Smith, chief of the DNR Fisheries Division. "Because the fish were so badly decomposed, however, it is still not certain that VHS caused these fish to die, since botulism was also a possible cause. But given the detection of VHS and the fact that the mortality occurred during the spawning season, both implicate VHS as the probable cause of death of these fish."

A number of Chinook salmon observed at the Swan River eggtake station last fall also showed signs of VHS infection, Mr. Whelan said, and fisheries managers report that standard disinfection procedures were effective in protecting other fish reared there. A standard fish health inspection that is conducted annually by the DNR Fisheries Division on this key broodstock did document VHS in both female and male fish, including one fish exhibiting clinical signs of VHS. Standard methods for disinfecting the eggs were applied last fall at the egg-take station prior to transfer of the eggs to the state's hatchery facilities. To date, all lots of Chinook salmon hatched from these eggs and being reared in DNR hatchery facilities have been tested and all are negative for VHS, which is attributable to the disinfection methods that have been employed at all the DNR's egg-take stations for many years.

"This shows that our standard disinfection procedures, similar to those used on the West Coast where VHS has been found for a long time, were effective in protecting our hatcheries and the fish reared in those hatcheries," Mr. Whelan said.

At press time Tuesday, January 30, state officials were still defining and coordinating the new steps that will be taken to control the spread of the disease.