Koi Herpes Virus in Minnesota Wild Fish

November 6, 2017

VDL Identifies Pathogen Responsible for Several Mass Mortality Events of Wild Fish in MN

In July of 2017, hundreds of dead common carp started washing up onto the shores of Lake Elysian near Mankato, MN; the ultimate death toll is thought to be in the thousands. This was the first of several mass mortality events involving wild common carp in Minnesota this year. In collaboration with the DNR and researchers associated with the Minnesota Aquatic Invasive Species Center (MAISRC) at the University of Minnesota, fish from several of these sites were brought to the University of Minnesota Veterinary Diagnostic Laboratory (VDL) for diagnostic testing. Each group of fish were tested for a number of pathogens. Ultimately, fish associated with several lakes in the region tested positive for Koi Herpes Virus (KHV). The Lake Elysian case was the first time that KHV has been detected in association with the mortality of wild fish in Minnesota.

KHV (also known as cyprinid herpesvirus-3) is a highly contagious OIE-listed aquatic pathogen that is known to cause disease – often resulting in high mortality – in koi and common carp. Expression of morbidity and mortality in koi and common carp from KHV appears to be highly dependent on water temperature, viral virulence, and the health of the susceptible population. The first reports of disease caused by KHV were in the late 1990’s in Israel, Germany, and the UK. Since that time, the geographical distribution of the virus has become much more extensive, and it is currently known to be present in much of Europe, Asia, and North America.

Although koi and common carp are not highly-valued commodities in the US compared to other aquatic organisms, the case of KHV spread around the globe highlights the importance of regulatory disease testing for cultured and internationally traded aquatic organisms generally. Investigators at the U of M VDL, including Dr. Alex Primus and Dr. Sunil Kumar, are working diligently to ensure that appropriate diagnostic tests are developed and employed to ensure the safety of both wild and cultured aquatic species in the US.

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