In light of the destruction caused by 2015’s highly pathogenic avian influenza outbreak, top U.S. Department of Agriculture scientists are studying the disease and how vaccines could play a role in containing it in the future.
Dr. David Suarez, research leader for exotic and emerging avian viral diseases research at the USDA Southeast Poultry Research Laboratory, shared the results of his team’s work studying the virus since the 2015 outbreak that rocked the U.S. layer and turkey industries. He spoke as part of Animal Health in the Heartland, a symposium on biotechnology’s role in emergency preparedness held July 20 in Omaha, Nebraska.
Dr. David Suarez, representing at the USDA Southeast Poultry Research Laboratory, speaks at the Animal Health in the Heartland symposium in Omaha. | Austin Alonzo
Suarez discussed the Southeastern Poultry Research Laboratory studies of the disease and its spread, effective vaccinations against avian influenza, and possible future innovations that could control the disease and preserve trade relationships.
Looking back on the 2015 outbreak
After researching the disease in chickens, turkeys and other bird species, it was concluded that ducks were likely the source of infection in the U.S. Suarez supports the theory that wild birds introduced the disease to domestic flocks and later outbreaks were transmitted from farm to farm. As the virus moved from bird to bird, Suarez said, it became more adapted, making it increasingly harder to control. This result supports the urgency of stamping out the disease quickly to prevent another large-scale outbreak.
Suarez said he believes the disease could persist in wild birds for three to five years, but so far there isn’t any evidence of the virus circulating among wild birds. That’s a positive, he said, but there is another migration season coming and, while the USDA tests a large number of birds, it’s only a small segment of the wild bird population.
Vaccine can control HPAI
As part of its research mission, the lab studied vaccines as a possible outbreak control measure. Suarez said if the outbreak becomes large enough, a vaccine could be administered to control the disease’s spread. The lab set out to see which currently available or developing vaccines might be useful against the disease.
In general, Suarez said, vaccines can be used to control the scale of an outbreak. If used as part of a larger plan, vaccines can greatly reduce disease shedding and cut the links of the disease transmission chain and, possibly, play a role in eradication of a disease. He said some countries, like Mexico, China and Vietnam, have vaccination programs but don’t use a comprehensive biosecurity strategy, and that can lead to avian influenza becoming endemic.
Even if an effective avian influenza vaccine is available, it would suffer the serious drawback of creating a possible trade barrier. Suarez said about 20 percent of U.S. poultry is exported and the country can often export the product cheaper than other countries can produce it. Many countries are looking for any reason to block U.S. poultry exports and protect their domestic industry, he said. An avian influenza vaccination program could be seen as evidence the disease is present in the U.S. and create a powerful non-tariff trade barrier.
After studying commercially available and emerging vaccines and biotechnology, the lab concluded the newer vaccines are better than the ones it started working with in early 2015, but they are still far from where they need to be.
As for practical vaccination, the best times for vaccination vary depending on the bird. For broilers, a single vaccination in ovo or at one day of age is needed; for layers and turkeys, vaccination at one day of age and then a booster at three to four weeks of age is needed. Layers may need an additional booster later in life. Suarez said there is substantial interest in developing vaccines for game birds, waterfowl, zoo birds and hunting raptors.
DIVA and the future of vaccines
Suarez said there is significant interest in developing DIVA (differentiate infected from vaccinated animals) vaccines, or vaccines that demonstrate the difference between vaccinated animals and vaccinated and then infected animals.
The vaccines would allow the U.S. to demonstrate to its trading partners that vaccinating birds does not mean they are exposed to the virus and give farmers the ability to remove exposed birds from the export market. Suarez said the country’s trading partners want clean birds with no chance of moving the virus through poultry products. Suarez said the vaccines would also need inexpensive tests to complement them. Ideally, the DIVA strategy would allow U.S. farmers to protect their flocks from HPAI and provide enough data to prove trade won’t spread the disease.
Beyond DIVA, other biotechnology improvements can be applied to poultry at a cost-competitive rate with vaccines currently being used. However, any vaccine will need to closely match the field strain to be effective. Commercial interest in developing avian influenza vaccines, however, remains low because a single vaccine produced year after year will likely not be effective against avian influenza consistently.
Coupled with effective biosecurity measures, a vaccine – bioengineered or not – could be an important part of an eradication strategy. The U.S. will need a DIVA strategy in place if it begins vaccinating against avian influenza, so developing the vaccine and the use plan is a long-term goal for the industry.