It appears that a strain of herpes is to blame for a large fish kill on a Minnesota lake recently. According to the local watershed and pathology tests conducted by the Minnesota Department of Natural Resources, Koi Herpes Virus was the culprit that caused the death of between "1,000 - 2,000 common carp and a handful of catfish, largemouth bass, and black bullhead observed dead."
The Lakes Foundation of Albert Lea posted about the large-scale fish kill on Fountain Lake in Albert Lea and the results of the tests conducted on the dead fish, they also expanded upon what Koi Herpes Virus is and what it affects.
The fish kill occurring on Fountain Lake has been verified by the DNR Pathology Lab to be caused by Koi Herpes Virus (KHV). Carp Edema Virus (CEV), another carp-exclusive virus that has often been found in conjunction with KHV-related fish kills, was not found in this case. Also noteworthy, Spring Viremia of Carp (SVC) was also not found. All three of these viruses are tested in these cases by the DNR Pathology Lab.
KHV is not known to impact other fish species, or impact humans. KHV is carried by carp species including Common carp, Goldfish, and Koi (a domesticated version of common carp). I had DNR staff on-site Tuesday and they boated the entire perimeter of the lake and it was reported there were 1,000 -2,000 common carp and a handful of catfish, largemouth bass, and black bullhead observed dead. However, we suspect those handfuls of other dead fish species (non-carp) were not related to this fish kill event. Unless something else shows up, we are confident this fish kill is exclusively common carp and caused by KHV.
KHV has been documented in many lakes throughout southern MN in the past 5 years. A large event on Lake Elysian in Waseca County the weekend of July 4th in 2017 was really when KHV made headlines and started to be tested more widely. At that time the KHV was identified by a UMN laboratory and was only 1 of a small handful of cases known in MN. Leading up to that, the DNR Pathology Lab did not have the equipment to test for KHV, so many carp-only kills were being diagnosed as caused by Columnaris, which in hindsight was likely only a secondary bacterial infection impacting carp that were already sick due to (possibly) KHV and/or CEV. The DNR Pathology Lab now has full capacity to test for these carp-related viruses and has been testing fish from most carp kills so long as fresh samples are available and submitted. This is the importance of good and timely reporting of fish kills by the public! So the point is we think this virus has been around a while and is relatively widespread and presents itself when the carp population and environmental conditions are ideal for the virus to induce a fish kill.