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Avian - 2001
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| Project Contact: | Sagar Goyal | Funding: | $87,000 |
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| • The Problem • Background • Mid-Year Progress Report • |
Respiratory diseases of turkeys are responsible for more than $35 million in losses to Minnesota’s turkey producers each year. This is a small but significant slice of a Minnesota poultry industry that employs more than 25,000 people and annually contributes more than $1 billion to Minnesota’s economy.
A respiratory disease caused by an avian pneumovirus (APV) has been spreading across the turkey production areas of Minnesota. It has caused losses of more than $20 million to Minnesota turkey growers since first diagnosed in 1996. This disease has not been reported in any other major turkey producing state. Thus, one of the greatest potential risks of this disease is the increased condemnation of birds and a ban of birds from Minnesota for foreign markets.
This year’s Rapid Response funding continues to build on emergency funding appropriated by the State Legislature in FY98 to:
Using this knowledge, a plan is being developed to constrain the disease from spreading to uninfected flocks.
Experience from pneumoviruses of humans, bovines and turkeys (Europe) indicate that live attenuated viruses are attractive vaccine candidates since they induce strong cellular immune response and provide better protection than killed vaccines. Therefore, we are concentrating our efforts on development of live attenuated APV vaccines by using many different approaches e.g., serial passages in vitro, cold adaptation, and temperature sensitive mutants. Under a field trail, we have been successful in reducing mortality and economic losses associated with APV in Minnesota by the use of serially passaged APV.
January 2001
Because of the economic losses associated with avian pneumovirus (APV), vaccine development has become a priority.
Progress on Candidate Vacines:
Passage 41 APV--This partially attenuated P41 provided protection to turkeys against challenge with virulent APV under experimental conditions. Mild to moderate clinical signs were observed in birds inoculated with this virus. This virus was further evaluated for its protective efficacy in commercial turkeys in controlled exposure experiments in seven counties.
P41 was inoculated by nasal and ocular routes in 10 turkey flocks at 2-4 weeks of age. Each flock consisted of 20,000-50,000 birds. Only tow birds per 1,000 were inoculated in each flock and the virus spread from inoculated birds to the entire flock within 10 days by bird-to-bird passage. Mild respiratory illness was observed in a few birds 12 days post-exposure in two of the flocks. Within three weeks post-exposure, all flocks were found to have APV antibodies.
One additional flock received the virus in drinking water, and antibodies were observed within 14 days.
P41 Impact--All flocks remained seropositive until 10 weeks post-exposure, with high levels of APV-specific neutralizing antibodies. Compared to unexposed flocks, medication cost and APV condemnation and mortality rates declined in P41-exposed flocks. When birds from these flocks were challenged with virulent APV under experimental conditions, no clinical signs were observed at 2, 6 and 10 weeks post-exposure. By comparison, respiratory illness and virus shedding was observed in unexposed control birds.
Passage 63 APV--To reduce pathogenicity associated with P41, we did further work and experiments testing for turkeys protection and safety. The resulting vaccine, P63, has been shown to be safer and more effective than P41. None of the birds inoculated with P63 showed clinical signs of APV and all the birds were protected against APV.
Preliminary studies in commercial turkeys indicate that no clinical signs are observed in birds inoculated with P63, and no outbreaks of APV have been observed in flocks inoculated with P63 vaccine in drinking water.
The use of two doses of P63 at 6-8 week interval to prolong protection is currently being evaluated.
Cold-adapted and temperature-sensitive mutants--There is a possibility of reversion of attenuated APV to virulent virus by bird-to-bird passage. To make safe and stable attenuated virus, we have adapted P63 to grow at 30°C and are developing temperature sensitive mutants that will not grow at 39°C.
Studies are ongoing to evaluate the cold-adapted mutants for safety and for efficacy against APV. We believe these mutants will not spread from inoculated turkeys to other contacted turkeys and will be safer vaccine candidates.