Pathobiological Studies of Trachea in Respiratory Infections of Commercial Chicken

Abstract

The repeated outbreaks of chicken viral respiratory diseases are a major cause of economic losses for the poultry industry. In this study, isolation and molecular identification of low pathogenic avian influenza virus, Newcastle disease virus, and infectious bronchitis virus were performed on suspected samples collected from 03 different sampling sites of poultry diagnostic laboratories in Lahore-Punjab. The current study was designed to screen the tracheal and lungs tissue simultaneously for four viral respiratory pathogens (AIV H9N2, NDV, IBV, and ILT) using the same PCR thermal conditions in a single reaction cycle. In this study, trachea and lungs samples of 413 chickens with history of respiratory signs were collected from one hundred poultry flocks. These samples were processed for RT-PCR and phylogenetic analysis to diagnose the respiratory pathogens including avian influenza H9N2 virus (AIV H9N2), Newcastle disease virus (NDV), infectious bronchitis virus (IBV) and infectious laryngotracheitis virus (ILTV). Based on RT-PCR results, number of positive samples for AIV-H9N2, NDV, IBV and ILTV were 14, 04, 05 and 0 respectively. In the current study, the detection rate of AIV H9N2, ND, IB, and ILT were 14%, 4%, 5%, and 0% respectively. Among these diagnosed viruses, no case of co-infection with studied respiratory viruses was detected. AIV-H9N2 strains detected in this study were placed in the same clade with G1-lineage viruses reported from Pakistan. Based on all essential analyses, the present study concluded that the evolution and distribution of the Newcastle disease virus of various genotypes VIIi and VIIl in Pakistan are having significant pathogenic potential. Our IBV isolate was placed in a single clade, which is representative of genotype-I lineage 13 (G1-13) of avian infectious bronchitis virus. The pattern of the severity of microscopic lesions induced in trachea and lungs was as follows; IBV>NDV>AIV-H9N2. The pattern of serum interferon-gamma levels in infected birds was as follows; IBV>NDV>AIV-H9N2. It is noted that the tracheal and lungs tissues are severely damaged in respiratory viral infection i.e. IBV>NDV>AIV-H9N2. Respiratory viruses currently circulating in commercial chicken flocks have maximum similarity with strains reported previously from Pakistan and neighboring countries like Iran and India. It is suggested that a single flock showing respiratory distress should be tested for multiple viral pathogens for accurate diagnosis. Suitable environmental conditions should be maintained to minimize health risks especially respiratory stress and tracheal damage to reduce predisposition to pathogens. This sensitive and specific molecular technique will provide in time and correct diagnosis that will save losses to farmers due to undiagnosed viral respiratory diseases. This study result also emphasizes to develop poultry vaccines from indigenous strains for better protection of commercial poultry in Pakistan. Circulation of various viral respiratory pathogens in the field is a serious threat to the poultry industry so continuous monitoring of flocks for respiratory viruses is key to the control of viral diseases.