Molecular Characterization of the Infectious Laryngotracheitis Virus (ILTV) Involved in Poultry Outbreaks Reveals the Virus Origin and Estimated Spreading Route

Infectious laryngotracheitis outbreaks have been observed in a short period of time in broiler, layer, and broiler breeder flocks, resulting in clinical signs and high mortality. The affected farms are located in the same geographical area, which is a high-density poultry region of Brazil. To estimate the potential origin of the virus or viruses that caused the outbreaks, the ILTVs detected at six companies were molecularly characterized by sequencing two fragments of the ICP4 gene and then compared with previous field and vaccine viruses detected in the country. The sequencing results revealed that all farms investigated were infected with a nonvaccine-origin virus. Phylogenetic analysis revealed that all farms were infected by the same virus classified as genotype VI. In addition, the ILTV detected in the present study was compared with that of viruses previously detected in egg-layer poultry regions in the country. The viruses detected in the recent outbreaks were indistinguishable, with one of them (VI-4) suggesting a possible route of transmission. This study describes for the first time severe ILT outbreaks in meat-type poultry in Brazil that spread quickly, and the phylogenetic analysis suggests the potential origin of the virus and route of transmission.