Antibody response of two populations of common carp, Cyprinus carpio L., exposed to koi herpesvirus.

Common carp, Cyprinus carpio L., exposed to koi herpesvirus (KHV) may become persistently infected and populations containing such virus-infected individuals may transmit the virus to other fish when co-habited. Detection of virus-infected fish in a population is thus critical to surveillance and control programmes for KHV. A study was therefore designed to detect anti-KHV serum antibodies, with an enzyme-linked immunosorbent assay, in common carp following experimental exposures to KHV under varying environmental conditions. The study determined that a proportion of fish within a population experimentally exposed to KHV (at least 10-25%) develop high antibody titres (1/1600 or greater) to the virus, and this immunological response was detectable for several months (observed at the termination of the experiments at 65, 46 and 27 weeks post-exposure). Furthermore, this response was detected in one population of fish that did not succumb to a high level of mortality when maintained at water temperatures that were non-permissive for KHV. Elevating the water temperatures to permissive conditions for KHV resulted in recurrence of disease despite the presence of anti-virus antibodies, suggesting that serum antibodies alone are not protective under the conditions of our trials.