Prevalence of low pathogenicity avian influenza virus during 2005 in two U.S. live bird market systems

Oropharyngeal and cloacal swabs were collected from poultry sold in two live bird market (LBM) systems to estimate the prevalence of low pathogenicity avian influenza virus (LPAIV) shedding during the summer and fall of 2005. Random sampling was conducted in three LBMs in Minnesota where 50 birds were sampled twice weekly for 4wk, and in three LBMs in a California marketing system. A stratified systematic sampling method was used to collect samples from Southern California LBMs, where LPAIV was detected during routine surveillance. No LPAIV was detected in the LBM system in Minnesota where realtime reverse transcription-PCR (RT-PCR) was conducted on oropharyngeal samples. RT-PCR was performed on swabs taken from 290 of 14,000, 65 of 252, and 60 of 211 birds at the three Southern California LBMs. The number of samples collected was based on the number of birds, age of the birds, and number of species present in the LBM. Virus isolation, subtyping, and sequencing of the hemagglutinin, neuraminidase, and other internal protein genes was performed on AIV-positive samples. The estimated prevalence of LPAIV in California was 0.345% in an LBM/supply farm with multiple ages of Japanese quail, 3% in an LBM with multiple ages and strains of chickens present, and 49.8% in an LBM with multiple species, multiple strains, and multiple ages. The positive virus samples were all LPAIV H6N2 and closely related to viruses isolated from Southern California in 2001 and 2004. Little or no comingling of poultry may contribute to little or no LPAIV detection in the LBMs.