The state Department of Natural Resources (DNR) recently confirmed the reappearance of the fish-killing pathogen viral hemorrhagic septicemia (VHS) in Clare County’s Budd Lake.
In the spring of 2006, VHS was responsible for large quantities of fish dying in Lake St. Clair, the St. Clair River, the Detroit River, Lake Erie, Lake Ontario, and the St. Lawrence River. In addition, the disease has also been confirmed in New York and Wisconsin bodies of water.
Since then, the DNR has been monitoring state waters for any sign of VHS. Only two inland lakes have turned up VHS-infected fish: Budd Lake in Clare County in 2007, and Washtenaw County’s Baseline Lake in 2009.
And now the pathogen has once again popped up in Budd Lake as the cause of a mass die-off of largemouth and smallmouth bass in April and May of this year.
Despite annual monitoring since 2007, the VHS went undetected through 2010. It’s unknown at this time if the virus has been present since the last time fish have died in such large quantities.
VHS — which can survive in water for at least two weeks — can be transferred through water via fish urine and reproductive fluids. It first starts by infecting gill tissue and then proceeds to the internal organs and blood vessels, which in turn become weakened and result in hemorrhaging of the internal organs, muscles, and skin.
Fish can also become infected with the virus by eating other infected fish.
According to the DNR, a low-level infection of VHS may not produce any noticeable symptoms in fish. However, as an infection becomes strong, fish begin beleeding throughout their body surface, including from their eyes, skin and fins. Interal organs also can begin bleeding. Sick fish also appear listless, swim in circles, and are often seen at the surface of the water.
The DNR notes that the disease doesn’t affect humans, whether you touch or eat an infected fish, because the virus dies at human body temperatures.
Extreme water temperatures, starvation, and spawning can lower fish immune responses.
The most likely vector of introduction was via ballast water exchange. However, it could also have been introduced by the movement of live fish and baitfish, as well as the natural migration of fish.
“These test results reinforce the continued need for anglers and boaters to follow our regulations that are designed to prevent VHS virus from spreading,” said acting DNR Lake Huron Basin Coordinator Todd Grischke. “It’s important that anglers and boaters not move live fish between waters, empty live wells and bilges when leaving a body of water, and disinfect and clean their equipment to prevent the spread of VHS virus to other waters.”
Despite the confirmation of VHS, new restrictions for Budd Lake are unlikely, according to DNR Fish Production Manager Gary Whelan.
“Regulations already in place since 2007 restrict the harvest and use of fish and baitfish from VHS-positive waters, and Budd Lake is included in that category,” he said.
For more information, including photos of clinical signs of infected fish, visit www.michigan.gov/vhs.