Avian Gyrovirus 2 and Avirulent Newcastle Disease Virus Coinfection in a Chicken Flock with Neurologic Symptoms and High Mortalities

A disease with severe neurologic symptoms caused 100% mortality in a small broiler operation in the Gauteng Province, South Africa in late March 2013. Routine diagnostic PCR testing failed to identify a possible cause of the outbreak; thus, samples were submitted for virus isolation, serology, and bacteriology. An avirulent Newcastle disease virus (NDV) strain isolated was identified as a V4-like genotype 1 strain, by DNA sequencing, with a cleavage site of (112)GKQGRQ down arrow L-117. Real-time reverse transcription PCR identified NDV in the brain but not in cecal tonsils or pooled tracheas, spleens, lungs, and livers. A random amplification deep sequencing of a transcriptome library generated from pooled tissues produced 927,966 paired-end reads. A contig of 2,309 nucleotides was identified as a near-complete avian gyrovirus 2 (AGV2) genome. This is the first report on the African continent of AGV2, which has been reported in southern Brazil, the Netherlands, and Hong Kong thus far. A real-time PCR for AGV2 only detected the virus in the brain but not in cecal tonsils or pooled tracheas, spleens, lungs, and livers. Sequence reads also mapped to the genomes of mycoplasma, Escherichia coli, avian leukosis virus subtype J, and Marek's disease virus but excluded influenza A virus, Ornithobacterium rhinotracheale, avian rhinotracheitis virus, avian encephalomyelitis virus, and West Nile virus. Air sac swabs were positive on bacterial culture for E. coli. The possibility of a synergistic pathogenic effect between avirulent NDV and AGV2 requires further investigation.