Infectious bronchitis virus: Emergence of nephro-pathogenic variant strains and vaccination failure in Pakistan

Infectious bronchitis virus: Emergence of nephro-pathogenic variant strains and vaccination failure in Pakistan

Muhammad Shahid & Prof. Dr. Aamir Ghafoor

Poultry sector is one of the organized and vibrant segments of agriculture industry of Pakistan. It is more commercialized than any other agriculture subsectors. There is more than Rs 700 billion investment in poultry industry. More than 1.5 million people have employments (direct/indirect) in this sector. Its contribution in agriculture and livestock value added stood at 7.5 percent and 12.7 percent, respectively.
Poultry meat is largely utilized and has a balancing role to mutton and beef. Its contribution in total meat is about 35%. Poultry meat is growing continuously showing a growth rate of 9.1% while egg production showed a growth of 5.6% during the last year as compared to previous year. Most of the poultry development strategy revolves around disease control. The transformation of poultry production from open shed system to controlled shed system is making an incredible difference in terms of quality and quantity of poultry production. Nevertheless, poultry farming is a high risk business in Pakistan which is subjected to instability, uncertainty and insecurity due to a number of reasons including regular outbreaks of infectious diseases.
Infectious Bronchitis (IB) is one of the major respiratory diseases of poultry having great economic impact on the industry. In breeders and layers, the disease has a negative effect on the productivity of laying birds while in broiler mortality, reduced performance, and secondary infections are of serious concerns. Infectious bronchitis virus affects three main body systems in poultry i.e. respiratory, female reproductive and kidneys. Respiratory clinical signs include depression, coughing, head-shaking and nasal and ocular discharges while necropsy findings include tracheitis, inflammatory lungs, and thickened cloudy air sacs. Death occurs from asphyxiation resulting from accumulation of caseous plugs in bronchi which mostly results from secondary infections.
IB is endemic in Pakistan and several classical and variant serotypes have been reported from various regions of the country. Some recent molecular studies have also reported the presence of new variants affecting respiratory system as well as kidneys of chicken with high mortality rates. Despite widespread vaccination, IB outbreaks are still very common indicating little or no cross-protection between different IBV serotypes.
University Diagnostic Laboratory (UDL), Institute of Microbiology, University of Veterinary and Animals Sciences (UVAS), is playing a key role in disease investigation and applied research for the control of such diseases. A research study was conducted under the supervision of prof. Dr. Aamir Ghafoor, Prof. Dr. Masood Rabbani and Dr. Hassan Mushtaq in Institute of Microbiology, UVAS, Lahore. New variants were isolated which were genotypically similar to the nephro-pathogenic strain of the neighboring countries i.e. India and China. Besides isolation and phylogenetic analysis, a clinical trial was also conducted to evaluate the cross-protection conferred by commercial vaccines against the isolated strains.
These isolates caused moderate to severe clinical signs in both vaccinated and unvaccinated chickens indicating the failure of the current vaccination program. However, a vaccination regime with a primary dose of classical and secondary dose of variant strain of IBV provided better protection as compared to a single or double dose vaccination with only classical strain. It is recommended that current vaccination regime against IB may be revised while further studies for development of vaccines from locally isolated strains is also suggested. To reduce the loss caused by IB, different stakeholders must play their active role in defining new and needful strategies for the control of this disease.

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