Hundreds of carp in a Michigan lake have died from a herpes outbreak

• Michigan's Department of Natural Resources says the koi herpesvirus is responsible for fish deaths in Lake Orion.
• The virus killed between 300 and 600 fish in July.
• The koi herpesvirus affects only the common carp, goldfish, and koi, and not humans.

Local authorities have gotten to the bottom of why hundreds of fish were found dead in Michigan's Lake Orion in July. The reason - koi herpesvirus, a deadly fish disease that kills off carp.

The Michigan Department of Natural Resources published the results of its investigation into the fish deaths last week.

The fish deaths were first reported back in late July when people spotted what they thought to be 250 to 500 dead fish floating in Lake Orion, a lake located north of Detroit. The Michigan Department of Natural Resources collected carp samples for testing on July 23 and received help from the Aquatic Animal Health Laboratory at Michigan State University to investigate the fish deaths.

The department estimated that in total, 300 to 600 adult carp died from the koi herpesvirus infections.

"As the case with most herpesviruses, koi herpesvirus is very specific on which fish species it will infect and only affects common carp, koi, and goldfish," said Gary Whelan, program manager at the Michigan Fisheries research division.

"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. Koi herpesvirus does not affect any other fish species and has no implications for any other birds, mammals, or humans."

According to the University of Florida's Institute of Food and Agricultural Sciences department, the koi herpesvirus is highly contagious among fish. It is spread to susceptible fish through the skin, including gill tissue. The virus itself kills fish within 24 to 48 hours of them displaying symptoms. Symptoms include fish lingering near the water's surface, swimming lethargically, and gasping for breath.

The Michigan Department of Natural Resources added in its September 17 statement that while fish viruses are typically not human pathogens, and cannot infect humans, freshwater fish like the carp should be fully cooked before being eaten.