Poultry viruses: from threat to therapy

Infectious diseases are one of the major causes of economic losses in poultry industries. In many instances, there are no specific signs that are associated with a particular disease. Besides clinical signs and findings from post mortem examinations, diagnostic tools based on serological and molecular detections are used to confirm the causative agents. However, the identification of causative agents and the detection of specific antibody responses in relation to a clinical problem are complicated due to the concurrent infections and improper use of vaccines. Currently, the poultry industry is threatened by more virulent viruses of endemic diseases or by exotic and emerging diseases that can cause major economic losses to this sector. The emergence and re-emergence of avian influenza virus (AIV), particularly the highly pathogenic avian influenza (HPAI) H5N1, the presence of endemic low pathogenic avian influenza (LPAI) H9N2 in poultry flock and recently the detection of the novel H7H9 and H10N8 in certain regions in China posed threats to the poultry industry and public health sector. Infection with HPAI such as H5N1 is easy to diagnose. However, the real challenge is to confront H7N9, H9N2, H10N8 and other LPAI which act in concert with other factors such as management, environment, nutrition and concurrent infections which possess a continuous threat to the entire poultry production system. The repeated outbreaks of diseases caused by variant strains of infectious bronchitis virus (IBV), velogenic Newcastle disease viruses (NDV) and more virulent viruses of infectious bursal disease virus (IBDV), infectious laryngotracheitis virus (ILTV) and Marek’s disease virus (MDV) in well managed poultry flocks have prompted the need to evaluate the underlying factors contributing to the failure of vaccinations to provide protection against clinical infections and transmission of disease. In the field, vaccination failure is a complex event involving various factors associated with vaccine strains and vaccination program, the virulence of field pathogens and the host immune competence. In many situations, immunosuppressive agents, primarily the MDV, IBDV and chicken anemia virus play an important role in increasing the susceptibility of chickens to opportunistic infections and/or suppressing effective vaccine induced responses. Vaccination is the most cost-effective method available in preventing economic losses and increasing the lifespan of animals. Undoubtedly, diagnostic tools, vaccines and vaccination equipment have improved over the years through the use of innovative technology. However, vaccine is not evolution-proof and it may enhance virus evolution especially in the absence of sterilizing immunity allowing wild type viruses to be transmitted through vaccinated chickens.Despite advancements in genetic engineered tools, conventional laboratory diagnosis using serological tests and conventional vaccines are used extensively in health and disease management of poultry. Nearly all poultry vaccines are conventional vaccines which consist of live-attenuated and killed vaccines that have generally worked well. However, avian pathogens continue to change and develop ways to evade the immunity induced by the current vaccines. In addition, as the poultry industry become more intensive, accurate, economical and practical laboratory diagnostic tools are important for the effective control of disease outbreaks. The advancements in the use of molecular detection method using real-time PCR approach, highly automated instruments for antibody detection and development of rapid on site assays for virus antigen detection may have significant impact in the field of disease prevention and control. In the area of vaccinology, most of the advances in the development of recombinant vaccines against poultry diseases are based on the development of recombinant viral vectored, DNA plasmid and reverse genetic vaccines. However, it is anticipated that more recombinant based vaccines will be used in the field in the near future. In addition, the advancement on “omic” technology are paving novel approaches for the development of new generation adjuvants and vaccines as well as breeding for disease resistance based on our improving knowledge of the chicken immunogenomic response to disease. However, the development and delivery of new or improved poultry diagnostics, vaccines and pharmaceutical which fulfill the industry, regulatory and public acceptance is a challenging process. Although the majority of poultry viruses are pathogenic to chickens, some of them especially NDV has the potential to act as a live saver in humans due to its unique properties as viral vectored vaccine against other infectious diseases and selective oncolytic properties on human cancer cells. The continuous encouraging results of NDV oncolytic virotherapy in human clinical trials will facilitate the approval of NDV as ancillary therapy of human cancer in the near future. Innovative research on the use of NDV as human vaccines and therapeutics should be explored via multi-disciplinary approach by various expert groups. In conclusion, as the poultry industry is expanding and the globalization of poultry and poultry by products, much is needed to improve the control and prevention of diseases. The emerging and emerging of diseases especially transboundary diseases can impact socioeconomic of a country and global food security. The strengthening our scientific and technical capacity, especially through innovative technology and strategy, will help to meet the current challenges and ever changing needs of the nation and the world.