Infectious Diseases 2020

Infectious Diseases 2020

USA: A(H7N3) virus in turkeys in North and South Carolina

Emerging Infectious Diseases Volume 26, Number 12 - December 2020 10 October, 2020

In March 2020, an outbreak of LPAIV H7N3 occurred in turkey farms, affecting 11 premises in North Carolina and 1 in South Carolina, USA. The initial decision to depopulate LPAIV-affected flocks was based on a risk assessment that included the location of affected premises, the poultry density in the area, and the presence of a basic amino acid substitution at the cleavage site among the initial LPAIV detections (PEKPKTR/GLF). During the ongoing response for this event, the Clemson Veterinary Diagnostic Center in Columbia, South Carolina, detected an influenza A(H7) outbreak in a second turkey location in South Carolina, with increased death and respiratory signs. On April 8, the National Veterinary Services Laboratories confirmed 1 of 6 pooled samples as HPAIV H7N3. Subsequent testing from all infected barns on the premises determined that HPAIV was present in only 1 of the 5 barns, but LPAIV was identified in the other 4 barns. All the premises affected by LPAIV and HPAIV H7N3 were located in 3 adjacent counties and 1 across state lines, indicating that geographic proximity was relevant to the outbreaks. Immediate depopulation was performed on affected LPAIV and HPAIV premises, affecting 361,000 birds.
Complete genome sequencing and phylogenetic analyses were conducted to trace the origin and evolution of the H7N3 viruses. For the 2 HPAIVs, 34 (5.7%) and 1,076 (38.8%) reads had no insertion, whereas the rest of the reads were found to have an identical 27 nucleotides insertion from host cellular 28S rRNA in the cleavage site. That means the virus mutated to the highly pathogenic form in 1 house on 1 farm via recombination with host 28S rRNA.