At the bottom of the page, additional resources from Drjohnson.com, How to Heat Koi With Koi Herpes Virus, Are They Cured?, A Video on Koi Herpes Virus (by me).

Hypothetically speaking, what happens if Koi Herpes Virus breaks out at Purpleton?

Lets say a major importer in Purpleton is buying large groups of fish from Southest Asia, and Israel, and Japan and then even from some Domestic partners.
Let’s say they sell to a dozen distributors across the United States.
And then let’s say the facilities in Purpleton are tested POSITIVE for Koi Herpes Virus.

The situation is a damn mess, then.

Here are (to me) the “Facts” that play in the situation:

Koi Herpes Virus has a “window” of temperatures that it “works” at. Lets’ just say that the active range is 71DF up to 81DF.
For some reason (And I have strong opinions and experiences on this) when the fish hit 83DF they turn around and ‘recover’ unless too far gone. Extremely high aeration is required. The fish should be kept at 83-84DF for at least 3 days.
Koi Herpes Virus kills 90% of affected fish in a week, when water temperatures are at or above 70-72 DF. The only reason I think that Koi Herpes Virus doesn’t kill ’em all is that by the time 90+ % of the fish are dead and gone there’s trouble for the virus getting from host to host.
Because Koi Herpes Virus doesn’t survive outside the Koi very long.
Koi Herpes Virus is “dose dependent” and takes a LOT of virus particles under the right conditions to create a fulminating infection with high morbidity and high mortality.
Koi Herpes Virus is a “reportable” disease, which means that EVEN if you didn’t want to tell anyone your fish or facilities had Koi Herpes Virus, too bad because the person who tested them SHARES the responsibility to report the positive test to the authorities.

A Seamy History of Koi Herpes Virus “Cured and Sold”.

When places in Taiwan, Vietnam, Hongkong, Thailand break with Koi Herpes Virus, it’s possible to buy Koi of high quality for literally pennies on the dollar. Vendors will race the clock to bring in tens of thousands of fish and heat them to 82+ DF in order to salvage the fish suffering only ‘loss of color in a percentage of the fish’ as a consequence. After the fish are heated, they’ve sold these fish into the domestic market. This has gone on for more than a decade. These vendors have had no blowback from KHV from these fish. They would know: “You Killed All My Fish” would be a hallmark experience, if the fish were carriers because ostensibly if the fish were typical carriers, they would cross-infect the entire pond in the following season as temperatures entered the active range again. For sure.

The Most Noble Way:

And lastly, when Taro Kodama had Koi Herpes in his livestock many years ago he sacrificed everything for the well being of the hobby. I considered that the single most noble thing I’d ever seen by a vendor or hobbyist. So he set a high bar for how you’re supposed to handle KHV when it happens.

Where are the liabilities?

Wholesalers:

Everyone who bought fish from the Wholesale in Purpleton are liable to have KHV in their facilities now. If they are not already above 72DF, they may experience an avalanche of losses when the water warms up.

Vendors

Of those distributors, any exposed fish that got sold to a residential hobbyist are liable to break with KHV when they warm to 72-73 DF

Hobbyists, Private Ponds

A residential hobbyist may have purchased a fish directly or indirectly that carries the KHV and may break with the virus later in the Spring when water temperatures hit 72 DF.

Should You Test?

If you want to know if your fish are carrying BEFORE they warm up, you’d get them tested. And then if the test is POSITIVE you have drawn a bullseye on your back and are subject to “whatever they’re doing with Koi” now, that have KHV which could be nothing, or everything.

Professionally I recommend testing. But I don’t know if I would do it personally, because the leighway for an invasive experience in my backyard pond is broad and unpredictable.

What Are the Options?

You could have your pond, fish and facilities tested and then strap in for the aftermath of ‘going public’.
You could kill everything in your shop or pond.
You could just kill all your Purpleton fish and anything exposed to them.
If I owned a shop with fish from Purpleton I’d get “some” of any batch I had from them, kept near them, on the same lot as them – and warm a generous sampling of them to 72DF and see if any mortalities are occurring by week’s end. (There’s a step-two for this*)
Watch pH and treat with API’s General Cure in order to head off anything that looked like “morbidity or mortality” from KHV when in fact it’s something dumb and easy like Ich or a crashed pH.

What Else Could I Do?

You Could “Po’ Man’s Cure Them”

You could heat the fish under high aeration up to 82-84 DF and bypass or leave the clinical illness phase. For some reason (And I have strong opinions and experiences on this) when the fish hit 83DF they turn around and ‘recover’ unless too far gone. Extremely high aeration is required. The fish should be kept at 83-84DF for at least 3 days.

The Israelis did some research on the virus and back in the early 2000’s they basically arrived at the following:

The virus has a soft, lipid capsule which disintegrates when heated.
They used heat to “cure” the fish while generating antibodies to make a vaccine (at the time) so they could have enough “degree days” to generate a strong immune response which involved infecting the fish, heating them, reinfecting them, heating them and reinfecting them. This is coming from a feeble memory but it says something: After heating, to get an infection – they had to RE-infect. The virus didn’t just ‘reactivate’ from latency when temperatures re-entered ‘the range’.
These fish could be sold as ‘vaccinated’ (through serial exposures and generation of measurable antibodies) and were not infectious to other fish (based on some testing which may or may not have impressed everybody.)

If I owned a shop with fish from Purpleton I’d get “some” of any batch I had from them, kept near them, on the same lot as them – and warm a generous sampling of them to 72DF and see if any mortalities are occurring by week’s end. (There’s a step-two for this*)

*What do you do with fish after quarantine at 74 DF, or after you heat them clean (if you actually are curing them at all?)

Some people would just destroy them.
Some people would hold them by, waiting til the following spring to see if they break with the disease. If they don’t break, then they’d sell the fish. Remember in the Purpleton scenario they were only exposed.
Some people would challenge the fish against SPF fish.

This is What You Do:

You get some fish from a place that is “pretty darn sure” the fish have never been exposed to, nor had KOi Herpes Virus. And you put representative fish from the Purpleton-Exposed-But-Managed collection into a generously sized tank with the SPF (Supposedly Pathogen-Free) fish at 72-73DF.

If the fish break with KHV (no matter which group) I honestly think you SHOULD destroy the fish.

If they’ve managed to get through the first seasons’ 72-74 warmup without clinical symptoms it bodes well for their probability that they were not infected. And THEN if they manage another warmup WITH vulnerable fish, and no clinical signs – there are some people who would consider the fish ‘safe’ (or at least as safe as any OTHER fish landing at LAX from Asia, Japan, Israel etc.)

I mean, I don’t think there are ANY fish that are 100% safe from a KHV standpoint. I’m sure that some vendors and distributors or wholesalers routinely test for KHV. But that’s not 100% unless the fish are absolutely isolated from the testing entity all the way to the hobbyists private pond. Is that even possible?

The following are articles that go deeper into Koi Herpes Virus. You might wanna know what the disease looks like. (Lethargy, erratic swimming at the surface, blistering skin, rotting fins and sunken eyes, mass mortalities over 6-7 fish at a time. 5-15% of the fish every day for a week.

Heating Koi With Koi Herpes Virus – How and Why
After Heating: Are the Cured or Hidden?
An Actual Discussion and First Hand Description From a Koi Herpes Virus Sufferer
Koi Herpes Virus is MUCH Worse Than SVC But Both Are Reportable.

EXCELLENT HEATERS

Hygger 1000W and HITOP 800W I’ve owned and used both.
The concept is that there’s a separate temperature probe <= a KEY component
And then titanium elements, which are extremely durable and non-toxic to fish.

https://amzn.to/3JWABUg <= A very good choice that has an external thermostat control and is VERY powerful but won’t kick a breaker. I’ve bought the 1200 and 1500W units and with almost anything else on the circuit they kick breakers. They can practically boil the water between the side of the tank and the element. I really prefer 800 to 1000W