barryian the sad truth is and Meyer will back me on this is nobody knows if our koi have the latent CyHV3 virus , it took 10 years for it to appear in the koi I told you about in our club whereas in the South African case it was just a few weeks the first thing like the case in our club is koi started dying 3 one day another three the next a further two the next it was then our health official recognised they had a suspected case of KHV [CyHV3] this was confirmed when he took two koi one dead the other alive for study and once the fish where autopsied it was immediately clear as to the reason their brains had turned to mush as had the insides , there are other tellers like heavy mucus, sunken eyes, gills that are totally shot to name just a few..
The problem is unlike the SVC Spring Viraemia of Carp [Rhabddvirus Carpio] which is a reportable disease world wide CyHV3 is not , its up to the individual Countries to make it a reportable disease.
Raising the pond temperature to 25.c then lowering it and raising it in rapid succession is one way to see if your koi break out with it , it is however it enters a dormant state at around 7.c
In South Africa they do things differently trying to bring it on by driving a Landrover or jeep at spead over rough ground to see if the stress caused by this activates it .
Srangely Meyer and I were talking via email about these very virusess just yesterday .
I put together an Article about the Latent CyHV3 [KHV] virus after learning of my friends distress it makes for intersting reading :-
https://www.gardenpondforum.com/articles/khv-cyhv3.27/
We all used the same dealership who were CyHV3 aware and went to great lengths to detect it but this slipped past them somehow we are all club wise hoping that our own koi where not infected but the truth is that nobody in the koi world knows if they have it or not
Dave