Vaccination of at-risk flocks of poultry in regions either inside or near quarantine zones can play a role in eradicating avian influenza, according to Dr. John Glisson, director of research, U.S. Poultry & Egg Association, and formerly the department head of population and health and avian medicine at the University of Georgia. Glisson said that most of the discussions with USDA Animal and Plant Health Inspection Service (APHIS) are now centered on answering questions about what the limitations would be on use of vaccination to ensure that it is used only as part of an eradication strategy with defined beginning and ending dates and a clear understanding of how, where and when the vaccines can be used.
Asking USDA for vaccination approval
While many within the poultry industry have focused on prior avian influenza outbreaks in Asia and North Africa where vaccine use was approved and the virus was never eradicated, Glisson pointed to the strategic use of vaccination in Italy as an example of a successful eradication effort. “It is clearly a disaster to vaccinate for avian influenza outside of an eradication program,” he said.
Glisson said that he didn’t expect any of the segments of the U.S. poultry industry to say that USDA shouldn’t approve the use of vaccination under any circumstance. He said that all segments of the industry just want to make sure any use of vaccination is done correctly.
Dr. Ron Prestage, veterinarian, Prestage Farms, former National Turkey Federation Chairman and current president of the National Pork Producers Council, said, “I am not in favor of carte blanche approval of the use of vaccination for avian influenza. I think that would be a disastrous mistake and would send the signal to your trading partners that you have lost control. But, you have to be able to separate the science from the trade issues.” He stressed that trade issues tend to be based on political science, not hard science.
He said, “I would normally say, be aggressive and put any infected flock down and get this under control, and they have been trying to do that. I am confident that USDA, state veterinarians, integrators and the growers in the affected states in their selfish best interest have been very aggressive and have been trying to do the very best job they can to get this under control. But, this virus does appear to be very infectious with very high shed rates and for some reason seems to very deadly for turkeys. How am I, with a good conscience, going to tell my industry brothers in the upper Midwest that are struggling with this outbreak to try and get it under control without vaccination simply because of trade?”
“Vaccination should be approved for use only in those areas where its use is deemed to be critically important and it should only be used for a very limited time, to stop this thing as fast as we can. Game plan A has not been working, so it is try to try game plan B,” Prestage said. “Now, people should not be allowed to start taking shortcuts. You shouldn’t be able to repopulate farms until the outbreak in the area is over. You shouldn’t repopulate until everyone is clean and ready to go.”
Dr. Jean-Pierre Vaillancourt, director, Research Group in the Epidemiology of Zoonoses and Public Health, University of Montreal, has worked with the poultry industry with prior avian influenza outbreaks in Mexico and British Columbia, Canada, and with eradication efforts of other infectious poultry diseases in North Carolina and Minnesota. He said that, given how the virus has spread in some regions, vaccination is worth looking at. He explained that a “firewall” of some kind needs to be established around the outbreak zones and that vaccination could play a role in doing this.
“I am usually not a fan of vaccinating as part of eradication, but I think that, in the U.S., it will be a temporary thing to help extinguish the virus,” Vaillancourt said. “I think it will be temporary.”
He stressed that vaccinated flocks can still become infected if exposed to the virus, but vaccination will reduce the rate of virus shedding. If vaccinated birds do become infected, they need to be euthanized, but they won’t shed as much virus and this can help stop the spread to other farms. “Vaccination will reduce the shedding, but it won’t stop it,” he said.
This avian flu virus is different
The story of the current avian influenza outbreak in North America starts in Asia. An H5N8 avian influenza virus is believed to have come across the Bering Sea after North American and Asian migratory waterfowl came in contact with each other somewhere in the arctic. The H5N8 virus then infected wild waterfowl in North America. Glisson said that the theory now is that, at some point, a wild bird was infected with a low pathogenic North American strain of avian influenza and the highly pathogenic H5N8 from Asia at the same time. The viruses then recombined and created the H5N2 strain that is causing the current outbreak.
“The virus we have now is actually a hybrid that is part from Asia and part from North America,” Glisson said. “It doesn’t make the ducks and geese sick but it does kill chickens and turkeys.” He explained that influenza viruses mutate or recombine frequently, so at some point the virus might change in wild birds into another strain, and the current strain might fade away eventually, but we can’t count on it happening.
“Perhaps the wild birds will get over it, but if they don’t, we could face a similar situation in the fall when birds migrate to southern regions,” Glisson said.
Prestage echoed Glisson’s concerns that poultry companies operating in southern states could be confronted with avian influenza virus in their locales later this year when waterfowl migrate south.
“We all have a selfish interest in getting this thing under control as quickly as possible,” he said.