Scientists from Israel have developed a vaccine for KHV which they say is safe to use as a prophylactic against the deadly virus.
The study, which was undertaken by Ayana Perelberg, Ariel Ronen, Marina Hutoran and Moshe Kotler of the Hebew University Hadassah Medical School in Jerusalem and Yoav Smith of the Ministry of Agriculture and Rural Development in Israel, has just been published in the journal Vaccine.
The team explain in the paper how they created a protocol to allow fish to be immunised against the virus using what's known as an attenuated virus.
An attenuated virus is, in simple terms, a weakened or less vigorous virus and may be capable of stimulating the immune system to create antibodies to the virus but without the strength to trigger an actual infection.
Carp are very sensitive to the virus and can pick it up simply by swimming in water in which it is present. However, infection is temperature specific so the fish that need to be immunised have to be kept at a specific temperature in order to contract the attenuated virus and pick up an infection that creates immunity against KHV.
To make the technique more effective and safer, the scientists did various bits of molecular jiggery pokery:
"In order to increase the number of random mutations in the genome of the attenuated virus, and thus, reduce the possibility of the attenuated virus reverting to pathogenic, we irradiated it and selected additional clones appropriate for vaccination.
"The results of our study suggest that a safe and efficient prophylactic vaccine can be developed by selecting an appropriate attenuated virus."
It may be a while before the vaccine becomes legally available in the UK.
Some experts believe that the Israeli fish could pose a risk to naive fish. However, many people in the trade believe that this may be the technique to adopt, and aren't experiencing problems with imported fish, or with the disease being passed on to naive fish in their wholesale and retail ponds.
Koi Herpes Virus, which was first seen in 1998 has caused mass mortalities in carp around the world, most notably in Israel, but most recently during a massive epidemic in Japan.
The virus is still currently unclassified and goes under two names, KHV (Koi Herpes Virus) and CNGV (Carp Nephritic Gill Virus). The name CNGV is becoming more widely used in scientific circles.
For more details see the paper: Perelberg A, Ronen A, Hutoran M, Smith Y, Kotler M (2005) - Protection of cultured Cyprinus carpio against a lethal viral disease by an attenuated virus vaccine. Vaccine. 2005 May 16; 23(26): 3396-403.