Vaccines are emerging as a tool for managing an increasingly broad range of poultry diseases even though the application of new vaccine technology is slow coming to the poultry industry, according to two speakers.

The “backbone” of today’s poultryimmunization programs remains developments that occurred during the postwar period from the 1950s through the 1970s, when the industry became intensified and new disease challenges emerged, said Dr. John Glisson, poultry veterinarian and professor at the University of Georgia, Athens.

The application of “high science” and new-generation vaccine technologies in the poultry industry has been hindered by a variety of factors. One is economics. Big poultry customers have used their buying power to drive prices down until some vaccines are “almost free,” he said.

This apparent lack of profitability with poultry vaccines has diverted research and development efforts toward potentially more lucrative areas such as companion animal or horse health. In addition, government funding for R&D in the poultry industry has fallen, prompting universities to spend less effort in this area, Glisson said.

Among other constraints to new poultry vaccine development are labor costs, he continued. “A lot of vaccines have to be injected, which makes them viable only for breeders or layers,” he said. “For broilers, labor costs generally preclude anything except mass vaccination at the hatchery or in the field. In the US, every time you pick up a bird, the labor cost is as much as 10 cents per bird.”

Vaccine opportunities

Despite obstacles to the development of new poultry vaccines, Glisson says there are opportunities. One of several examples he cited is in the area of food safety.

“Consumers aren’t interested in Newcastle disease or Marek’s, but they do know about campylobacter and salmonella,” he noted. “There’s an opportunity to do more to help producers reduce the risk to humans from these pathogens.”

He sees potential for in ovo vaccines, too. They have their limitations because some viruses may be harmful to the embryo and maternal antibody interference can be an issue, but they also present great opportunities and may provide a route for economically viable mass vaccination.

A combination of high-energy diets and the withdrawal of antibiotics is allowing a number of diseases to blossom, such as clostridial enteritis, colibaccilosis and coccidiosis — again, presenting opportunities for new vaccines, Glisson said.

Mapping of the chicken genome is significant. “But don’t get too excited,” he warned. “Development will be incremental and, when it comes to using genetics, disease control will always take a back seat to feed conversion and growth rates.”

Existing vaccines ‘extremely good’

A similar message came in a separate presentation. The UK’s Dr. Ian Tarpey, R&D manager for virology at Intervet/Schering-Plough Animal Health, predicted that there will be progress in new poultry vaccines, but it will not be revolutionary.

Many of today’s poultry vaccines have been used for years, in part because many of them are still “extremely good,” he said. He also said that change in the field of poultry vaccines may seem slow because expectations, which are often fueled by breakthroughs in human vaccines, are simply too high.

Economics is a constraint to vaccine development, Tarpey agreed with Glisson. “This is a low-cost business, so we can’t use high technology if no one will pay for it.” New vaccines will have to provide the same or better economic performance as current vaccines. They will need to be broad-spectrum and in the right combinations for different regions.

“Add to that issues about poultry welfare, regulations, unique geographical needs, consumer fear of genetically modified organisms and politics, and there are many other factors constraining new vaccine development,” Tarpey said.

Nonetheless, he is optimistic about poultry vaccine development and outlined up-and-coming technology that may yield new vaccines to fill industry needs.

Improve adjuvant design

The technology used now to stimulate an immune response is about 40 years old and could be improved upon, Tarpey said. Adjuvant design is one area where this could occur.

Another approach known as immunomodulation could focus on changing the bird’s ability to respond to a vaccine.

“Chickens have many of the same chemical messengers that mammals have — the information flow between cells needed in an immune response,” he said. This work has already been pursued by several groups, though improvements to immune responses demonstrated in the laboratory experiments have yet to be translated into new vaccines.

The importance of cell-mediated immunity should not be underestimated, Tarpey added. Mucosal immunity, which is important in the gut, would be another area with potential for improved vaccine performance.

Molecular biology

Molecular biology is an area of science that has held promise for poultry vaccines for the past 20 years. Most progress has been made on DNA viruses, which are relatively easy to manipulate. A number of recombinant vaccines are now licensed in the US and doing well.

In the future, some recombinant vaccines may well be based on ribonucleic acid (RNA) viruses. These could have a number of advantages including mass applicability, a fast response and limitation of virus shedding.

Another area of focus is improved knowledge of microorganisms. “We are starting to understand how microorganisms survive and replicate in the host. Reverse engineering — identifying what the organism does to survive — could be used to either augment this process in the live vaccine or to engineer it out of the virulent organism to attenuate it,” he said.

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