Detection of Laryngotracheitis Virus in Poultry Flocks with Respiratory Disorders in Slovenia

Abstract

Infectious laryngotracheitis (ILT) is an acute, highly contagious infectious disease of the upper respiratory tract in chickens and other poultry species that causes significant economic losses in countries worldwide. Between 2017 and 2019, seven outbreaks of mild to severe respiratory disorders with high suspicion of ILT occurred in commercial and backyard poultry flocks in Slovenia. In all submissions, infection with ILT virus (ILTV) was confirmed by PCR, which is the first report of ILT in Slovenia. Circulating ILT strains were characterized by the sequence and phylogenetic analysis of two fragments of the ICP4 gene. Four strains-three detected in non-vaccinated flocks and one in a flock vaccinated against ILT-were identical or very similar to the chicken embryo-origin live virus vaccines, and the other three were closely related to Russian, Chinese, Australian, and American field strains and to tissue culture origin vaccine strains. As in other diseases, coinfections with other respiratory pathogens in confirmed ILT cases may cause a more severe condition and prolong the course of the disease. In our study, coinfections with Mycoplasma synoviae (7/7 tested flocks), infectious bronchitis virus (5/5 tested flocks), Mycoplasma gallisepticum (4/7 tested flocks), Ornithobacterium rhinotracheale (3/4 tested flocks), and avian pox virus (1/2 tested flocks) were confirmed, indicating the importance of these pathogens in the occurrence of ILT infections.

Keywords: chicken; infectious laryngotracheitis; mixed respiratory infections; partial ICP4 sequencing.

Figure 1

Gross pathological findings in submitted hens: (a) Fibrinous oculonasal discharges; (b) Severe fibrinous to caseous tracheitis.

Figure 2

Phylogenetic relationships as calculated on partial ICP4 gene nt sequences of ILTV strains detected in Slovenia and ILTV strains derived from the GenBank database. (a): Phylogenetic tree on the fragment of ICP4 gene as amplified by primers ICP4-1F and ICP4-1R. (b): Phylogenetic tree on the fragment of the ICP4 gene as amplified by primers ICP4-2F and ICP4-2R. Both phylogenetic trees were generated by the neighbor-joining method with the Kimura-2 parameter substitution model and 2000 bootstrap replicates to assign confidence levels to branches. The scale bar indicates substitutions per site. GenBank accession numbers are given before the strain names. The nucleotide sequences obtained in this study are underlined. Phylogenetic analyses were conducted with MEGA X [25].

Figure 2

Phylogenetic relationships as calculated on partial ICP4 gene nt sequences of ILTV strains detected in Slovenia and ILTV strains derived from the GenBank database. (a): Phylogenetic tree on the fragment of ICP4 gene as amplified by primers ICP4-1F and ICP4-1R. (b): Phylogenetic tree on the fragment of the ICP4 gene as amplified by primers ICP4-2F and ICP4-2R. Both phylogenetic trees were generated by the neighbor-joining method with the Kimura-2 parameter substitution model and 2000 bootstrap replicates to assign confidence levels to branches. The scale bar indicates substitutions per site. GenBank accession numbers are given before the strain names. The nucleotide sequences obtained in this study are underlined. Phylogenetic analyses were conducted with MEGA X [25].