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Avian - 2003
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| (Print Friendly Version) |
| Project Contact: | Sagar Goyal | Funding: | $65,000 |
| Devi P. Patnayak |
District:
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Unknown |
| • The Problem • Background • Objectives • Final Report • |
Several approaches can be used to develop a live, attenuated vaccine (e.g., serial passages in cell cultures, cold adaptation at low temperatures, development of mutated strains by chemical or site directed mutagenesis, and the development of gene deletion mutants). Several promising mutants have been evaluated and found to not meet the needs of the turkey industry for an effective, easily administered, single dose vaccine that will not revert back to a virulent state. Additional work is needed to develop and evaluate other mutated strains for their safety and effectivness as live attenuated vaccines.
A summary of Avian Respiratory Disease Research Progress (1998-2001) is available. See also the project topic page for 2002.
To develop a live vaccine against APV, researchers serially passaged a Minnesota isolate of APV in cell cultures for 63 times. This serially passaged virus (designated as P63) was shown to be safe and effective under experimental and field conditions (Patnayak et al., 2002b) and has now been licensed by the USDA for use in commercial turkeys.
To further enhance the efficacy of live vaccine, researchers developed a cold adapted strain of APV by serial passages of passage 41 APV at gradually lower temperatures. This virus has been adapted to grow at 300C and has been designated as ca virus. The ca virus was evaluated under experimental conditions and was found to be safe and effective in 2-week-old turkey poults (Patnayak et al., 2002a). To determine the optimum route of vaccination, researchers inoculated one-day-old turkeys with oculo-nasal, oral and aerosol routes. On subsequent challenge with virulent APV, vaccinated birds by all three routes withstood challenge as no clinical signs and virus shedding were observed in vaccinated birds while non-vaccinated birds developed clinical signs and shed the challenge virus in their respiratory secretions.
To determine the duration of immunity provided by the vaccine, birds at one-week of age were vaccinated with ca virus followed by challenge with a virulent strain of APV at 3, 7, 10, and 14 weeks post vaccination. At all ages, birds were found to resist challenge with virulent virus as indicated by the absence of virus shedding in all vaccinated birds.
In another study, six in vivo back passages were given to a batch of 10 birds (at each back passage) to ensure that the attenuated strain does not revert back to virulence. However, the birds at each back passage were found to shed virus indicating that in spite of vaccine being protective experimentally, it has the potential to revert back to virulence. In summary, researchers have developed a live vaccine of APV that has been licensed and a ca strain of APV that has been found to be protective against APV although it does have the potential to revert back to virulence.