BackgroundPoultry are exposed to viruses all the time. Most don’t cause any harm, but some pose a serious threat to poultry health. Vaccines, along with genetic selection, good husbandry and biosecurity, play a crucial role in managing this threat. When one of these vaccines is administered, the bird’s body is presented with specific components of the pathogen, which elicit an immune response. These components, or “antigens” are often based on a protein on the surface of a virus. Once presented with the antigen, the bird’s immune system “remembers” it and is primed to launch an attack if the protein shows up again, such as when an intact virus infects the body. A moving target While many such vaccines have been effective, designing an effective vaccine against Avian Influenza (AI) virus has proven to be a challenge. The AI virus is very prone to changes to its genetic backbone that, in turn, can sometimes change the structure of its proteins. If the protein on which the vaccine was based changes enough, the immune system will not recognize it as a previous offender, resulting in a slower, less aggressive response. A look at the virus life cycle reveals the potential for an alternative control strategy: Avian Influenza virus consists only of a set of genetic instructions (RNA), a coat of protein that protects the RNA and a surrounding envelope. Like all viruses, it does not have the chemical machinery necessary to reproduce itself. It instead relies on a host cell to read its genetic instructions and produce new virus particles. The newly formed virus particles move on to infect neighbouring cells and the process repeats. If one were to prevent the cell from reading the virus’ genetic instructions, the infection cycle would be interrupted. Dr. Serguei Golovan (now at the University of Delaware), Dr. Grégoy Bédécarrats, Dr. Shayan Sharif, Dr. Éva Nagy, Arusyak Abrahamyan and Serguei Duvanov at the University of Guelph have been developing technology that does just that.
OutcomesStopping AI in its tracks The researchers are exploiting a process known as RNA interference (RNAi). RNAi is a natural mechanism present in many animals, including birds, that can decrease the activity of specific cellular genes and has been shown to serve as a natural antiviral response. Drawing from information gleaned while studying the RNAi process, the researchers devised a strategy to target and decrease the activity of AI virus genes when they are present in the cell. They introduced into the cell short strands of RNA designed specifically to associate themselves with protein complexes within the cell and at the same time physically bind to specific regions of RNA strands from the virus. Normally the avian cell would treat viral RNA as any other and modify it, transcribe it, then translate it into proteins; this is how AIV “hijacks” the cell’s machinery and gets it to make new virus particles. When the appropriate RNAi molecules are present, however, the viral RNA is tied up with the complexes and degraded before the cell’s machinery can access it, thus preventing production of new virus proteins. Previous work funded by the Poultry Industry Council and the Ontario Ministry of Agriculture, Food and Rural Affairs developed a model system for assessing efficiency of RNAi molecules in cells grown in the lab. Subsequent work has shown that the RNAi molecules developed can indeed significantly reduce the replication of AI virus in chicken cells, but the level of reduction is not nearly as high as seen in mammalian cells. Several design changes were then made to the RNAi molecules in an effort to improve their performance in avian cells.
ApplicationWhat’s next Once sufficient performance is achieved in the lab, the molecules will be tested to see if they can reduce AI virus replication in the bird. RNAi technology has been shown to be effective against human influenza virus and Dr. Golovan previously recorded promising results in the pig. Although several technical hurdles must still be overcome before the technology is used in poultry, RNAi may one day be among the tools available to control AI.
Funding$75,600 (CPRC $25,200, NSERC/AAFC $50,400)
PublicationsArusyak Abrahamyan, Éva Nagy, and Serguei P. Golovan. 2009. Human H1 promoter expressed short hairpin RNAs (shRNAs) suppress avian influenza virus replication in chicken CH-SAH and canine MDCK cells. Antiviral Research 84: 159-167.