Francisco Ríos

Ángel Mosqueda Taylor

Recombinant vaccines could help poultry producers in Latin America improve control of Newcastle disease and infectious laryngotracheitis, according to experts speaking at a recent poultry respiratory disease symposium held in Cuzco, Peru.

Despite vaccination, Newcastle disease (ND) alone still accounts for about two per cent and three per cent of the total yearly mortality in Mexico, reported Francisco Ríos, a biologist and technical service manager, MSD Animal Health, Mexico.

"If we are talking about a yearly production of about 1.5 billion broilers, that's millions and millions of dollars lost," Dr Ríos said. For layers, he added, the average loss due to ND is about 15 per cent but can be as high as 25 per cent. "The curious thing is that the hens do not die from ND, they just don't lay."

Conventional vaccination programmes are costly and problematic on many farms, he continued. As an example, broilers are often vaccinated against ND at least once with an individually applied, inactivated vaccine, which can potentially cause serious local reactions and increase labour costs. Handling the birds also causes stress, which can reduce daily weight gain.

Most poultry companies also apply at least two live ND vaccines. While effective, these vaccines can cause severe respiratory distress and interfere with infectious bronchitis vaccines if they are not timed properly.

Control of infectious laryngotracheitis (ILT), which is endemic in major poultry-producing countries including Brazil, Argentina, Colombia, Mexico and Peru, is equally challenging, Dr Ríos said. The consequences of conventional ILT vaccination include potential respiratory reactions and, with some of the vaccines, house-to-house spread of the ILT virus; the result is reduced bird performance.

Conventional vaccines for ILT and ND have to be applied separately, sometimes spaced several weeks apart depending on the situation. "Given the short life span of the broiler, this complicates vaccination schedule planning," Dr Ríos said.

Ángel Mosqueda Taylor, DVM, MPVM, a veterinary consultant and former professor of poultry diseases at the National Autonomous University of Mexico, said that problems in his country due to Newcastle disease (ND) are much like those elsewhere in Latin America. The disease has a significant economic impact because the consequences of ND include mortality, chronic respiratory problems, condemnations and export obstacles.

Low-virulence ND tends to cause respiratory signs and lesions; it also leads to secondary bacterial infections and may hinder reproductive ability. The high-virulence form of ND is associated with depression and anorexia, secondary bacterial infections, respiratory, digestive, nervous and reproductive signs, such as poor shell and egg quality, secondary bacterial infections and mortality, Dr Taylor said.

Controlling ND in Mexico is difficult for a variety of reasons that include poor communication among producers, excessive field challenge in some areas and an abundance of backyard birds and live bird markets that are reservoirs for the disease, he explained.

New Vaccination Programmes

One way to improve control of ND, Dr Taylor said, is by incorporating a recombinant vaccine into the vaccination protocol.

One of several field cases he cited involved repeated outbreaks of ND on a Mexican broiler farm. "These were not simple outbreaks; they were sometimes complicated by avian influenza (AI) and/or infectious bronchitis viruses, as well as Escherichia coli and, in some cases, mycoplasma," he said.

After a new vaccination plan was implemented that incorporated the recombinant vaccine Innovax ND-SB and a live Ma5 infectious bronchitis vaccine, mortality dropped from 24.5 per cent to 5.5 per cent, Dr Taylor said.

A trial with the recombinant vaccine was also conducted in a flock with a low ND challenge and no avian influenza. The objective was to determine if use of an emulsified ND vaccine could be avoided. When the field-vaccinated birds were challenged at the laboratory with the virulent Chimalhuacán ND strain at 21 and 35 days of age, they were 100 per cent protected, while unvaccinated birds used as a control in the laboratory challenge trial had zero per cent protection, he said.

Dr Taylor emphasised, however, that "for vaccines to work at their utmost ability...bird susceptibility and the field challenge need to be reduced and the success of a vaccine partly depends on how it is placed inside your vaccination programme."

Robert Teeter

Luis Etcharren

Aris Malo

Reduced Stress

The symposium included speakers from Latin American countries and the US who are using recombinant ND or recombinant ILT vaccines with good results. By replacing some conventional vaccines with the recombinants, which do not cause side-effects, there is less stress on birds due to fewer reactions from conventional vaccines and less handling of birds, they said, as well as less labour required for conventional vaccine programmes.

Studies presented by Robert Teeter, PhD, a nutritionist at Oklahoma State University, USA, appear to confirm the impression that less stress from conventional vaccines is beneficial. Broilers that received Innovax-ND had significantly better weight gain and feed conversion early in life, less heat production and higher protein, fat and net energy values when compared to several conventional and killed vaccines for ND.

"The first two weeks after vaccination appear to be critical for vaccination impact, and the recombinant had less impact than all the other vaccines, especially during those first seven days," he said.

Return on Investment

Dr Ríos said that the recombinant Innovax vaccines decrease the viral load in the environment, improve vaccine uniformity and do not interfere with conventional vaccines for other respiratory diseases. Flocks have solid protection against all known ND genotypes.

"Add up the cost of conventional ND vaccines, associated labour costs and export restrictions due to poor disease control. When you consider that switching to one dose of the recombinant removes all these negatives from the equation, the recombinant represents a good return on investment for both broilers and layers," he maintained.

Luis Etcharren, DVM, global marketing director at MSD Animal Health, added that avoiding post-vaccination reactions and the need to treat flocks in the field translates into savings of about five cents per bird. In addition, hatchery application of vaccines can reduce vaccine failures.

Dr Ríos reminded producers that two HVT vaccines cannot be used together. If ILT is the bigger problem, he advises replacing conventional ILT vaccines with the recombinant Innovax-ILT, which has the same advantages as Innovax-ND.

Aris Malo, DVM, global technical services director for poultry, MSD Animal Health, who has extensive experience managing respiratory disease in poultry, explained how the recombinant Innovax vaccines work.

They are based on DNA recombinant technology and their backbone is the herpesvirus of turkey (HVT). HVT serves as a carrier for a donor virus, which is inserted into the HVT genome. For Innovax-ND, the donor is the 'fusion' ND virus gene and for Innovax-ILT, it is the 'I and D' ILT virus genes.

The 'SB' in Innovax-ND-SB represents the live serotype 2 (chicken herpes virus) Marek's disease vaccine strain SB-1 strain, which has been added to enhance immunity against very virulent Marek's, he noted.

Besides causing no reactions, Innovax vaccines can be administered in-ovo or subcutaneously and they work despite maternal antibodies, Dr Malo added.

"With conventional ND and ILT vaccines," he said, "we have to revaccinate repeatedly because of the short duration of immunity. Some of the live vaccines spread in the field, which can result in lost performance. We've all see the local reactions that can occur with killed ND vaccines, which also hike up manpower costs because they have to be given individually to birds. We don't have most of these problems with the recombinant vaccines."

Ariel E. Vagnozzi

Laura Villarreal

HVT versus FPV

Ariel E. Vagnozzi cited research he conducted as a post-doctoral research associate at the Poultry Diagnostic and Research Center at the University of Georgia.

Compared to a conventional chicken-embryo-origin vaccine, Innovax-ILT as well as a fowlpox virus (FPV)-vectored vaccine both provided partial protection. However, after birds were challenged at 57 days of age, clinical scores five days later and the viral load three days later were significantly better with Innovax compared to the FPV vaccine.

"The HVT recombinant adequately mitigated clinical signs after challenge with a virulent strain of ILTV and induced a slight reduction in viral load in the trachea. There was no difference in induced protection whether the HVT recombinant vaccine was given in-ovo or subcutaneously," he said.

Laura Villarreal, DVM, regional manager, MSD Animal Health, Latin America, said that by improving zootechnical results, the recombinant vaccines are contributing to sustained growth of the poultry industry.

Further Reading Find out more information on the diseases mentioned in this article by clicking here.