Efficient vaccine against the virus causing a lethal disease in cultured Cyprinus carpio.

We have isolated a virus, which causes a mortal disease in cultured ornamental Koi and Common carps (Cyprinus carpio) in many countries worldwide. This unclassified virus, which causes nephritis and gill necrosis, and so has been given the name carp nephritis and gill necrosis virus (CNGV), has a morphology resembling the herpes virus, but bears a genomic DNA of ca 250-300 kbp. So far, both others and we have been unable to find CNGV-DNA sequences possessing a significant similarity to known DNA viruses. The virus induces a lethal disease when water temperature ranges between 18 and 25 degrees C (permissive temperature). In this report, we demonstrate that carps, exposed to the virus at 23 degrees C for 3-5 days and then transferred to the non-permissive temperature of 30 degrees C, became resistant to a challenged infection and their sera demonstrated a high level of virus-specific antibodies. We have isolated attenuated non-pathogenic viruses that render virus-vaccinated carps resistant to the disease. Furthermore, vaccinated fish developed high levels of antibodies against the virus. We suggest, therefore, that this attenuated virus could be used as a live vaccine for the eradication of the mortal disease afflicting Common and ornamental carp fisheries in many countries.