Comparison of nucleic acid-based detection of avian influenza H5N1 with virus isolation

Nucleic acid sequence-based amplification with electrochemiluminescent detection (NASBA/ECL) of avian influenza virus was compared with viral culture in embryonated chicken eggs. Virus was isolated from blood or anal swabs of chickens artificially infected with highly pathogenic avian influenza A/Chicken/Hong Kong/1000/97 (H5N1). Viral nucleic acid was detected in blood samples by NASBA/ECL immediately prior to death, whilst nucleic acid extracted from anal swabs was detected from the day following artificial infection until death. Thus, blood and/or anal swabs are a suitable source of material for the detection of avian influenza in dead birds, but anal swabs are more suitable for detection of viral genetic material in live birds. Dilution of a known viral standard was used to determine the limit of sensitivity for both NASBA/ECL and egg culture detection methods. The NASBA/ECL method was equivalent in sensitivity to egg culture. The NASBA/ECL results agreed with egg culture data in 71/94 (75.5%) tissue samples obtained from artificially infected birds.