Revolutionising notifiable avian disease diagnostics: validation of direct swab testing for Avian Influenza and Newcastle disease using the CENOS platform

Abstract

Existing molecular diagnostic approaches for notifiable avian diseases (NADs) involve a suite of PCR assays that enable both generic detection, and where positive, subtyping of both avian influenza virus (AIV) and Newcastle disease virus (NDV). Novel rapid and direct diagnostic assays for the detection of AIV and NDV were developed and evaluated using unprocessed cloacal (C) and oropharyngeal (OP) poultry swab material. Both assays employ a closed tube direct real-time reverse transcription polymerase chain reaction (RRT-PCR) approach in which viral lysis is achieved by heat treatment and a dedicated PCR compatible buffer, followed by detection using a RRT-PCR approach. Primer and probe sets were designed using globally circulating AIV and NDV sequences collected over the preceding five years, rather than region-specific sequence datasets, so that the assays detect all circulating genotypes. Analytical performance assessment demonstrated that both assays were highly sensitive and specific, successfully detecting all unextracted target antigens without cross reactivity to a panel of other common poultry pathogens. For each assay, viral lysis and amplification were achieved directly from samples at single digit genome copy numbers. Furthermore, low levels of viral RNA could be reliably detected in the presence of C and OP matrix material, providing proof-of-concept for direct detection of these economically significant avian pathogens in a field setting. Additional use case scenarios, including pooled sample screening and combined C/OP testing from individual birds, were also explored. These findings establish a foundation for ongoing studies incorporating paired-sample testing against validated laboratory reference assays.