Survey of infectious laryngotracheitis outbreak in layer hens and differential diagnosis with other respiratory pathogens

Trachea, lung, and conjunctive samples from 51 commercial layer farms from Bastos region, São Paulo, Brazil, were submitted to nested-PCR and virus isolation in SPF chicken embryos for ILT diagnosis. This region experienced an outbreak characterized by respiratory signs, decrease in egg production and increased mortality. Out of the 51 tested field samples, 23 were positive for ILT by nested-PCR, 22 were positive after the virus isolation, and 24 were positive when both techniques were used. Newcastle disease virus, Avian pneumovirus, or Mycoplasma gallisepticum were not detected. Infectious bronchitis virus was detected in one farm and Mycoplasma synoviae was detected in eight farms. The high incidence of infectious laryngotracheitis virus (ILTV) detection, the high correlation between the observed clinical signs and the ILTV detection, and the results of differential diagnosis demonstrated that ILTV was the causative agent of the outbreak of respiratory disease observed in Bastos region, São Paulo, Brazil