Evaluation of different embryonating bird eggs and cell cultures for isolation efficiency of avian Influenza A Virus and Avian paramyxovirus serotype 1 from real-time reverse transcription polymerase chain reaction–positive wild bird surveillance samples

Virus isolation rates for influenza A virus (FLUAV) and Avian paramyxovirus serotype 1 (APMV-1) from wild bird surveillance samples are lower than molecular detection rates for the specific viral genomes. The current study was conducted to examine the possibility of increased virus isolation rates from real-time reverse transcription polymerase chain reaction (real-time RT-PCR) using alternative virus isolation substrates such as embryonating duck eggs (EDEs), embryonating turkey eggs (ETEs), Madin–Darby canine kidney (MDCK) cell cultures, and African green monkey kidney (Vero) cell cultures. Rectal swabs of birds in the orders Anseriformes and Charadriiformes were tested by real-time RT-PCR for the presence of FLUAV and APMV-1 genomes, and virus isolation (VI) was attempted on all real-time RT-PCR–positive samples. Samples with threshold cycle (Ct) ≤37 had VI rates for FLUAV of 62.5%, 50%, 43.8%, 31.5%, and 31.5% in embryonating chicken eggs (ECEs), ETEs, EDEs, MDCK cells, and Vero cells, respectively. A higher isolation rate was seen with ECEs compared to either cell culture method, but similar isolation rates were identified between the different embryonating avian eggs. Virus isolation rates for APMV-1 on samples with real-time RT-PCR Ct ≤37 were 75%, 100%, 100%, 0%, and 37.5% in ECEs, ETEs, EDEs, MDCK cells, and Vero cells, respectively. Significantly higher VI rates were seen with ECEs as compared to either cell culture method for all real-time RT-PCR–positive samples. Because of the limited availability and high cost of ETEs and EDEs, the data support the continuing usage of ECEs for primary isolation of both FLUAV and APMV-1 from real-time RT-PCR–positive wild bird surveillance samples.