Clinical and Genetic Characterization of Infectious Laryngotracheitis Virus in Layer Chickens in Basrah, Iraq

Infectious Laryngotracheitis (ILT) has been widely prevalent in numerous countries in recent years. The present study aimed to detect ILT in chickens exhibiting clinical suspicion, utilizing molecular analytical techniques in Basrah, Iraq. Clinical signs, histological changes, and polymerase chain reaction (PCR) were used to diagnose thirty-five samples collected from clinically suspected chickens, including trachea and lungs for histopathology and PCR testing for the p32 gene. The present study demonstrated that the three isolates of ILTV, including ILT-BASRAH 1, ILT-BASRAH 2, and ILT-BASRAH 3, caused the typical signs and pathological changes of ILT in layers chickens. Phylogenetic analyses indicated that ILT-BASRAH 1 exhibited a distant relationship with other current local isolates. Conversely, the isolates ILT-BASRAH 2 and ILT-BASRAH 3 exhibited a close relationship with each other. The initial results indicated that ILT-BASRAH 1 exhibited high nucleotide similarity to MK895003.1, MK895000.1, and MK894999.1 from Australia, which are representative of recombinant strains derived from live attenuated vaccine strains, as well as PQ232589.1 from Georgia. Furthermore, ILT-BASRAH 2 and ILT-BASRAH 3 were identified as vaccine-related isolates. These isolates demonstrated a high level of genetic similarity and a close phylogenetic relationship to the Gallid alphaherpesvirus 1 isolate TJ2019 (GenBank accession no. PP062931.1), originating from Chinese source flocks. The current study determined that ILT-BASRAH isolates 1, 2, and 3 exhibited genetic similarity, suggesting that they likely originated from the same or closely related sources. Their difference from vaccine strains, including the minor variation in ILT-BASRAH 1, might indicate regional viral adaptation.