Detection of koi herpesvirus (KHV) after re-activation in persistently infected common carp ( Cyprinus Carpio L.) using non-lethal sampling methods

Surviving carp which had recovered from KHVD were kept for approximately eleven additional weeks at 20°C water temperature. To induce KHV re-activation, carp were subjected to netting stress on day 81 after infection and gill swabs and dropping samples were collected daily for investigation by quantitative real-time PCR. An increase of KHV concentration of up to 1000 KHV genomic equivalents was detected over a three day period post-netting from these non-lethally collected samples. A considerable decrease in KHV genomic concentration was observed after day four post-netting. KHV DNA was not detected in samples from persistently infected carp on day 10 after stress induction. The results of this study suggest that KHV DNA is more readily detected, in gill swabs, one to three days after stress induced by capture and netting.