Recombinant vaccines against ND and ILT

Biologist Francisco Ríos, technical director for Intervet/Schering-Plough Animal Health, (ISP-AH) Mexico, said that in his country, where Newcastle disease (ND) is “arguably the most economically important poultry disease in the country,” testing indicates that highly pathogenic, velogenic strains of the virus are circulating. Some conventional vaccination programmes for these strains do not always provide adequate protection. “As an example, broilers have to be vaccinated against ND at least once with an individually applied, killed vaccine, which may cause local reactions in some flocks,” Ríos added.

“That extra handling can also stress birds and run up labour costs. If not timed properly, some live ND vaccines may cause severe respiratory distress, increase medication expenses and also add to labour costs.” In contrast, studies indicate that one properly applied dose of the recombinant vaccine Innovax* protects birds from virulent ND. Birds protected from virulent ND have been shown to grow faster and more uniformly, Ríos said.

Safe alternatives
Infectious laryngotracheitis (ILT), which is highly contagious and causes problems ranging from mild respiratory signs to mortality of an entire flock, is equally worrisome, veterinarians said. Dr. Guillermo Zavala, a veterinarian with the University of Georgia, USA, said ILT has increased in multiple countries throughout the Americas, affecting all segments of the commercial poultry industry. Recombinant vaccines, Zavala said, “are safe alternatives” that provide acceptable protection without the disadvantages associated with some CEO vaccines.

Dr. Aris Malo, veterinarian and global technical director with ISP-AH who has extensive poultry experience in Latin America, explained that Innovax vaccines utilise the herpesvirus of turkey (HVT) to carry ND or ILT antigens that induce immunity. HVT is known to be safe for chickens and also protects against Marek’s disease.The recombinant vaccines are administered in ovo to 18-day-old embryos or at hatch by the subcutaneous route. “They cause no side effects, don’t interfere with other respiratory vaccines and don’t spread in the field. By eliminating the need for field vaccination, they simplify management and save producers on labour costs,” he said.

Level of protection
Malo cited studies conducted with Innovax demonstrating that the level of protection provided is similar to that found with live and inactivated ND vaccines.

Dr. Keith Honegger of ISP-AH, reported that ILT outbreaks are occurring in certain areas of the US and that losses can be severe, especially in unvaccinated flocks. The recombinant ILT vaccine has already been used extensively with success in both commercial broiler and layer flocks. “The benefits observed by producers when the recombinant is used in place of conventional vaccines include elimination of ILT field vaccination, elimination of reactions and less ILT disease issues, which in turn may improve livability and feed conversion,” Honegger said.

Metabolic impact
Dr. Robert Teeter, a researcher from Oklahoma State University, USA, who has extensively studied energy utilisation in broilers with the aid of sophisticated metabolic chambers, said that since feed costs are rising and further gains in feed formulations are becoming increasingly difficult, producers need to find non-nutritive factors that can be manipulated to improve energy utilisation.

He pointed out that disease could result in the expenditure of thousands of calories, while vaccination to prevent disease costs typically less than 50 calories. Teeter believes that in the future, it will be possible to achieve a feed conversion ratio of about 1, a goal that will be affected in part by vaccine choices. To this end, Teeter is embarking on studies to discover if some vaccines are “kinder and gentler” than others regarding their impact on the development of immunity and energy expenditure.

Avoiding post-vaccination
Dr. Luis Etcharren, a veterinarian and director of the poultry business unit for ISP-AH in Mexico, said that recombinant vaccines reduce metabolic expenditure by reducing the need to handle birds for revaccination in the field or medication as a result of vaccine reactions. “Avoiding a post-vaccination reaction and the need to treat a flock translates into savings of about 5 cents per bird,” he said. In addition, hatchery application of vaccines can reduce vaccine failures. “The return-on- investment when using recombinant vaccines is well-justified. In some field cases, analysis showed it was as high as 5:1,” Etcharren said.

Dr. Laura Villarreal, regional poultry manager for ISP-AH, said the recombinant vaccines help birds achieve their genetic potential, enabling producers to provide high-quality animal protein.“It’s important for producers to understand the new technology of recombinant vaccines because it can maximise profitability by protecting flocks against serious diseases without adverse effects,” she said.

Biosecurity crucial
Dr. Angel Mosqueda, an independent poultry consultant, pointed out that control of disease, particularly virulent (velogenic) ND, is needed if poultry producers want to export poultry products. Obstacles in Latin America to good control of virulent ND include poor biosecurity, lack of communication and cooperation among producers since they do not share information when an outbreak occurs, commercialisation and intensified production of the poultry industry as well as badly designed control programmes. “Outbreaks are occurring with no reporting in some countries,” he said, “because there isn’t an incentive to report nor indemnification, or because the producers involved do not export their products.”

Re-evaluation of current ND disease programmes are warranted and to achieve improved ND control, new technology such as recombinant vaccines need to be combined with good biosecurity, and the understanding that good sanitary procedures are needed not only within individual farms, but between farms. Therefore, this is not only a problem of biosecurity, but also of communication and cooperation among producers and between producers and sanitary authorities, he said.