Asia’s poultry producers gain insights into respiratory disease
Approaches to better understanding and preventing respiratory infections come under the spotlight in Taiwan
Controlling infectious bursal disease (IBD) is key in any control program for poultry respiratory diseases. IBD replicates in the bursa, one the two primary lymphoid organs of birds, and is the “school of the lymphocytes,” playing an essential role in the development of the humoral immune system, said Dr. Michel Bublot, research project and technology platform leader with Merial France, speaking at last year’s Merial Avian Forum Asia.
However, vaccination against IBD using live vaccines can cause some problems, he continued. Live IBD virus has to replicate in the bursa of Fabricius to trigger the production of antibodies, and live IBD vaccine causes some damage to the bursa.
Examining the evolution of IBD vaccinology, Bublot explained that new biotechnologies have been employed to develop the third generation of IBD vaccines based on the HVT virus, widely used to prevent Marek’s disease, and that this vaccine technology provides protection against two major immunosuppressive diseases – Marek’s disease and IBD.
Turning to infectious bronchitis (IB), Professor Yongchang Cao, of Sun Yat-sen University in China told delegates that the virus still changes continually by mutation or recombination and that more than 700 strains of IB had been isolated and identified by the university laboratory between 2010 and 2013.
He continued that since new types of IBV, such as QX-like strain, are the predominant threat to poultry flocks, producers should use novel and high-quality IB vaccines for prevention and control, adding that, in trials, it had been shown that vaccination with two antigenically distinct live-attenuated vaccines could result in broad cross-protection against many different IBV types.
Where complex respiratory disease is concerned, delegates were told that avian metapheumovirus (aMPV), commonly known as swollen head syndrome, can often be a contributing factor, but is often misdiagnosed due to the involvement of IB or other pathogens. There is no treatment for aMPV-infected chickens, but the use of antibiotics can help in reducing secondary infections and severity of disease. However, live and inactivated vaccines against aMPV are available, and their use can reduce ill health and losses.
Vaccination as a tool for buying time in the control of avian influenza was looked at by Dr. David Swayne, director of the Southeast Poultry Research Laboratory, U.S. Department of Agriculture.
He explained that most highly pathogenic avian influenza (HPAI) epizootics have been eradicated using a traditional stamping-out program, but that since 1995, five epizootics have added vaccination as an additional, interim control tool.
“Eradication is the only control strategy,” he stressed. “Vaccination should only be seen as a tool to manage disease, but it does make diagnosis more difficult. Vaccination’s role in eradicating avian influenza is to buy time, and only for when biosecurity doesn’t work.”
Where mycoplasma is concerned, control is problematic due to vertical transmission in fertile eggs and horizontal airborne transmission. However, vaccination is now seen as an alternative to total control. Using vaccination can displace routine antibiotic use in layers, delegates learned, as well as in breeders and their progeny. The example was given of a commercial layer producer in Asia who had managed to achieve a 4 percent saving in feed costs after adopting vaccination, which more than paid for the mycoplasma vaccination costs.
Vaccines must be applied properly, and Dr. Ryan Izard, chief science and technology officer with Animal Science Products, told delegates that failing to manage the numerous risks that exist among all water supplies, such as oxidizers, pH and osmotic balance, can reduce vaccine effectiveness and leave holes in a flock’s immunity. New generations of stabilizers for drinking water, spray and eye-drop vaccination, he said, can help to protect vaccines from several risks.
When protecting birds against respiratory disease, any vaccination program needs to go hand in hand with a robust biosecurity program, monitoring and surveillance, and delegates were told that biosecurity was “not only science, but an art and culture."
For proper control of respiratory disease, good diagnostic tools need to be employed. Dr. Rafael Monleon, business unit manager (poultry) with Biocheck, explained that, due to its relatively low cost and capacity for mass screening, the ELISA test is widely used to diagnose disease.
When looking at abnormally high titers, he said, there are three key criteria that have to be met to conclude that the serolody obtained is the result of a field challenge.
First, he said, the mean titer post-infection should be significantly increased. A good rule is that the mean titer post-infection must be at least twice the level expected after vaccination, or at least twice the mean titer before infection. Second, the mean coefficient of variation (CV) should be significantly below the levels expected after vaccination, or significantly below the CV levels before infection. Third, the clinical signs must match the serology. For example, if there is elevated IBV serology, but there are no clinical signs of disease, nor signs that do not match IBV, an IBV challenge cannot be confirmed.