The detection of infectious pancreatic necrosis virus in asymptomatic carrier fish by an integrated cell‐culture and ELISA technique

. The need to accurately, reliably and economically screen large populations of brood salmon for infectious pancreatic necrosis virus (IPNV) prompted a fresh approach to the use of ELISA and cell cultures. The result is an integrated procedure that recognizes the limitations of each method while building upon the strength of both in the way that they are brought together, ELISA tests can never be sensitive enough to detect the very low virus levels typical of carrier fish, but are able to detect virus in infected cell cultures, both specifically and objectively. Cell cultures provide the means to detect very low virus levels, but without specificity and only through subjective observation. Without a suitable ELISA, the need to keep cell monolayers in a condition in which viral effects can be observed imposes strict demands on inoculation and culture procedures. In contrast, the new procedure described in this paper provides a simpler culture method in which the inoculum is retained throughout a single, uninterrupted 14‐day culture cycle. This culture duration allowed maximum opportunity for viral replication in healthy cells, even though the monolayers became disorganized. However, the cultures were tested in the standardized ELISA, eliminating the need for microscopic observation and virus neutralization tests. Thorough validation studies confirmed the system's adequacy in practice.