The spread of KHV (Koi Herpes Virus) can be easily prevented by making sure that your nets are completely dry before you use them. The virus can not survive long if it is not kept damp and, during the summer months, this can be easily done by hanging your nets out as soon as you get home.
The picture above is from the last Junior event at Luckfield. What you can see here are two nets that were given to Juniors to borrow, one net that wasn't used , but it got wet from the ones that were in the bag, the weigh sling and unhooking mat and a one other unhooking mat that was left behind at the lake (Let me know if it is yours?). On the ground is the bag that the nets were in. Not shown are any landing nets or cradles because I didn't use any. But they would be hung out in the same way. Everything is hung out on the washing line to dry out thoroughly or, if it is raining or winter time, I will leave them there to be washed through by the rain. I will even give everything a blast with the hose pipe to be double sure that any nasties are washed away.
If your nets are still wet when you get to a match or a fishing session where you are using them, extend them on the ground before you put them in the water, even if it's raining. This will show that you have been a responsible angler, and done your best to keep the fishery that your are visiting, safe.
KHV is not harmful to humans, but it can be, and often is, fatal to fish. Obviously this can be a disaster for a fishery if KHV takes hold.
Fish with KHV disease may show the following signs, especially when water temperatures are between 16 to 28 °C:
necrotic (white or brown) patches on the gills
rough patches on the skin and sloughing mucous