Epidemiologia e caratterizzazione genetica della Laringotracheite Infettiva negli allevamenti avicoli italiani

Infectious laryngotracheitis (ILT) is a major respiratory disease affecting poultry, caused by the ILT virus (ILTV). This condition poses significant challenges to poultry health and productivity. This study aimed to assess the prevalence of ILTV in chicken populations and genetically characterize the circulating strains to differentiate between field and vaccine strains, evaluating the effectiveness of current vaccination programs. Archived samples collected over the years from intensively raised chickens were selected, and DNA was extracted for analysis. A real-time PCR was developed, validated, and applied to detect and quantify the presence of ILTV. Positive samples underwent further amplification and Sanger sequencing of two genomic regions to distinguish between field and vaccine strains. The findings revealed that out of 90 samples, 29 were positive for ILTV. The concentration of the ILTV genome in these samples varied significantly, ranging from 0.49 genome copies/µL to 881,524.1 genome copies/µL. Samples with higher viral titers were more easily sequenced, allowing for strain characterization. As expected, the sequencing success rate decreased in samples with lower viral amounts. Most detected strains were identical or closely related to live vaccines commonly used in Italy. This suggests that the applied vaccination strategies were effective in preventing the circulation of virulent field strains. However, the persistent circulation of vaccine or vaccine-like strains still poses some diagnostic challenges and complicates the interpretation of the epidemiological scenario because of the difficulty in differentiating them with routine diagnostic techniques. Moreover, the potential for residual pathogenicity or reversion to virulence, leading to clinical outbreaks, remains a risk that requires further investigation.