Importance of IBV surveillance for protection against diseases

A study was designed to observe tissue tropism and pathogenesis of infectious bronchitis virus (IBV) and Avian Influenza A virus (H9N2) in a single as well as in mixed infection in commercial broiler chicken in Punjab, Pakistan. IBV and H9N2 suspected samples were collected from different outbreaks of diseases during 2018. The result of phylogenetic analysis revealed that the identified IBV isolate belong to genotype G1-24 and showed 100% homology with the Indian strain 236 while it showed 77-81% homology with currently used vaccinal strains in Pakistan. The identified H9N2 virus showed more than 95% resemblance with already reported H9N2 viruses isolated during 2015-2016. The virus belongs to B2 lineage of Mideast group-B.

To investigate the pathogenesis and tissue tropism in the commercial broiler chickens, 125 chicks were divided into 6 groups of 25 each. Single and mixed infection of IBV and H9N2 was given to first five groups in different combinations while the 6th group served as a negative control. Five birds were slaughtered on day 3, 5 and 7 PI and trachea, lungs, kidneys and intestines were collected from the slaughtered birds.

Histopathological examination revealed different combination of lesions in single H9, single IBV and mixed H9 and IBV infections. Immunohistochemical staining was done to detect the presence of viruses in the trachea, lungs, kidneys and intestine in single and mix infection groups. The results revealed that the most severe lesions were seen in single IBV infected group while the lesions in the mix infection groups and H9 infected group are mild than the IBV infected group.

Effectiveness of three most commonly used commercial vaccines against circulating field isolates of H9N2 and IBV was evaluated. Sixty one-day old broiler chicks were obtained from a commercial hatchery and were divided into four different groups A, B, C and D. At seven day age, H9N2 and at zero day IBV vaccines and at 14 day Bioral H120, Merial was given to all birds of group A and C respectively while group B and D were kept as positive control for H9 virus and IBV respectively. At 21 day age, antibody titer was evaluated by ELISA. Higher ELISA antibody titer was observed in vaccinated groups (A (0.759) and C (0.272)) while low antibody titer was observed in non-vaccinated groups (B (0.183) and D (0.017)). At day 28, H9 challenge was given to group A and B while IBV challenge was given to group C and D. At day 28 and 35, five birds from each group were slaughtered; organs were taken, preserved and processed to observe histological changes. Tissue changes like congestion, infiltration of inflammatory cells were observed in the non-vaccinated groups while the birds of vaccinated groups showed mild histological changes.

The study conducted at University of Veterinary & Animal Sciences Lahore showed that most commonly used commercial vaccines provide effective immunity against recent isolates of H9N2 and IBV in broiler chickens.

—Ghulam Mustafa & Dr Asim Aslam