Hundreds of Carp in Single Lake Died From Outbreak of Herpes, Investigation Finds

An investigation completed by the Michigan Department of Natural Resources (DNR) last week found that a herpes outbreak killed hundreds of carp in Lake Orion this past summer. Officials reassured residents that the outbreak doesn't pose a threat to humans or other wildlife.

According to a public statement released by the DNR on September 17, between 300 and 600 adult carp were found dead in Lake Orion in July. The deaths — which were brought to the DNR's attention by locals — prompted the DNR, in conjunction with the Aquatic Animal Health Laboratory at Michigan State University, to collect samples and conduct an investigation.

Last week, it was determined that the fish were killed by an outbreak of koi herpesvirus.

Koi herpesvirus is a highly contagious, water-borne virus, says Australia's Center for Invasive Species Solutions (CISS) on the website PestSmart.

"After a fish is infected by the virus, the virus multiplies in the fish for about seven days (depending on the water temperature)," says CISS. "During this time the fish eats and appears quite normal."

Once a carp displays the first signs of the disease, however, it only takes 24 hours for the fish to die.

Gary Whelan, program director for the Michigan DNR Fisheries Division, told Detroit Free Press that the virus spreads through gills, as well as through excretion.

"If you're in the neighborhood, you get infected," Whelan said.

Whelan said it was likely that the virus spread as a result of someone releasing a pet goldfish or koi into the lake.

Though the outbreak was strong enough to kill hundreds of carp, Whelan assured locals in the DNR's public statement that the koi herpesvirus doesn't pose a threat to humans or other wildlife.

"As the case with most herpesviruses, KHV is very specific on which fish species it will infect and only affects common carp, koi and goldfish," he said. "This is only the third detection of this non-native virus in Michigan waters, and it is known to kill large numbers of its host species at times. KHV does not affect any other fish species and has no implications for any other birds, mammals or humans."

Still, the DNR reminds people to follow best practices when cooking and consuming fish caught in the lake. Whelan also encourages residents to avoid disposing of pet fish into the lake. Instead, he told Detroit Free Press, euthanize fish humanely by putting them in the freezer.

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An investigation completed by the Michigan Department of Natural Resources (DNR) last week found that a herpes outbreak killed hundreds of carp in Lake Orion this past summer. Czanner/iStock