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Wild birds play a role in spreading avian influenza, Newcastle and infectious bronchitis viruses to domestic poultry, and strict farm biosecurity programs and appropriate vaccination strategies are critical for their control.
The recent outbreak of highly pathogenic H7N3 avian influenza in the Mexican state of Jalisco provides a serious reminder of the impact that a disease outbreak could have on the U.S. layer industry. At time of press, a reported 2.5 million chickens had either died or been euthanized as the industry and government in Mexico work to contain the spread of the virus.
Dr. Ilaria Capua is the director of the research and development at the Istituto Zooprofilattico Sperimentale delle Venezie in Italy, which hosts the United Nations Food and Agriculture Organization and Office International des Epizootes reference laboratory for avian influenza and Newcastle disease. Capua discussed the latest developments in the battle against three of the poultry industry’s most prolific diseases—avian influenza, Newcastle disease and infectious bronchitis—at the International Egg Commission’s conference in Venice, Italy.
“Avian influenza is the most devastating disease there is in the animal kingdom. This virus is capable of killing 100 percent of the birds it infects in 48 hours, causing extreme suffering to the animals,” said Capua. It has been almost a decade since the highly pathogenic strain of H5N1 influenza first emerged in Southeast Asia, and Capua and her research team are dedicated to the fight against it. “We have to do everything we can to make sure that this disease is eradicated from the face of the earth,” she said. By 2007, H5N1 had spread from South East Asia to Europe and Africa; Capua said that this was the first time in history that a highly pathogenic virus had spread to three continents. Data gathered from January 2011 to March 2012 shows that this strain of H5N1 is now present in a limited number of countries; with the exception of Egypt, Israel and Iran, outbreaks are now mainly present in Asia, and predominantly in Southeast Asia. H5N1 is endemic in at least six countries.
Indonesia has reported the most avian influenza outbreaks, and Capua believes that it probably has the most complicated situation because it is a nation made of thousands of islands. China, Bangladesh, Vietnam, India and Egypt have also reported cases.
H5N1 lessons learned
It is now known that the H5N1 virus prefers cold to heat; its peak is always during winter months, and it survives better in a cooler environment.
H5N1 has not been as big of a problem in developed countries because they have the systems and infrastructure in place to manage it better. However, H5N1 is now a disease that is mainly affecting developing countries. Capua said that Egypt faces a very difficult situation; the recent social unrest in the country means that many of the people now responsible for managing and controlling the outbreaks are new to their jobs, and they are facing very challenging situations with limited previous experience.
During the past 10 years, the avian influenza virus has changed, and it will continue to do so. Capua said that this is good news, as well as bad. The good news is that as part of this evolution of the virus, some strains, clades, have disappeared. However, the bad news is that other clades are evolving, particularly in certain countries.
During viral evolution, the viruses change so fast that it is very difficult to identify appropriate vaccination strategies to keep the infection under control. Capua said, “Viruses change; they change very much, especially if you are using a vaccine. They change like the caterpillar changes into a butterfly. We are doing extensive monitoring to try to understand which vaccines are going to be most efficient in controlling the disease.”
H5, H7 and H9 subtypes
There has been an outbreak of H5N2 in ostriches in South Africa. So far, this is proving very difficult for the industry and South African authorities to control, as many of the tests used on poultry are not suitable for ostriches.
During the past year, Capua said that there have been 55 reported outbreaks of low pathogenic avian influenza, including H5, H7 and H9. She explained that H5 and H7 are notifiable strains due to their ability to mutate. H9 is proving to be a large problem for the layer and broiler industries in the Middle East and Far East. When the H9 virus combines with other infections, the case mortality can be very high. Capua’s laboratory is currently trying to understand why H9 is wide spread, and is trying to establish a way to eliminate it.
What’s next for avian influenza?
Capua said that H5N1 is still a concern; the problem is far from over, and because of the role that wild birds play in the spread of the disease, it is particularly hard to get rid of. However, improvements have been made; at the beginning of 2003, there were 40 countries infected, and this has been reduced to six to ten countries infected today.
Avian influenza strains of H5 and H7 are still present, and Capua said that these two viruses are probably being under reported today; she believes that there are more cases of H5 and H7 than have been reported. Generally, H5 outbreaks are mostly reported in Africa, and H7 cases are mostly reported in Europe. However, it is H9 that Capua believes poses the most serious potential problem—she told the International Egg Commission that she believes H9 will be the virus that she and her team will have to work on the most in the future.
Newcastle disease was first identified back in 1926. Despite being around for such a long time, the Newcastle virus still has the power to cause devastating effects; the 2002/2003 outbreak in the U.S. caused over 4 million birds to be depopulated. Recent figures show that in 2011, only 18 countries didn’t report an outbreak of Newcastle disease.
The vaccine for Newcastle disease is the most produced vaccine in the world. However, Newcastle disease still poses a major threat and is still a significant problem for the egg industry.
Capua described Newcastle as an acrobat virus, “it likes to go from one species to another. It can infect many, many different types of birds.” Pigeons in particular are a main carrier of the disease.
Genotype VII is a new variant of Newcastle disease, and there are reports from countries that this new variant has killed laying hens. Genotype VII is an antigenic virus; it appears the same to the birds’ immune system as Newcastle disease, although it affects it in a different way.
Capua urged egg producers to ensure that their vaccination programs are thorough and up to date. She explained that at the moment there is no reason to believe that the vaccines currently available should not protect against Genotype VII, if they are administered at full dose, and appropriately. However, it is likely that flocks not vaccinated properly will be susceptible to this strain of Newcastle more than others.
Newcastle disease shares many features in common with other infectious diseases, like influenza. Because of the new genotypes that are emerging, Capua believes that there is a need to do better surveillance and increase bio-security. She also explained that vaccine strategies need to be tailored depending on the variant of the virus; a very aggressive virus needs a vaccination program capable of stopping the virus from killing birds.
Infectious bronchitis virus
Infectious bronchitis is present all over the world. One of the biggest challenges of infectious bronchitis control is the fact that the virus has so many variants. Having so many variants also makes it incredibly difficult to classify. Infectious bronchitis virus has been found in different countries, appearing to be exactly the same variant of the virus, but having completely different names.
Capua described the infectious bronchitis virus as a chameleon virus, able to change its appearance, continually forming new variations. Several research groups around the world are trying to develop vaccination programs using two different types of the infectious bronchitis virus. The hope is that by using a combination of variants, the vaccine will be able to protect against new and emerging strains of the virus.
World-wide surveillance program
Capua’s laboratory has established a world-wide infectious bronchitis surveillance program. The program receives isolates from the Middle East, Europe, South America, Latin America and most recently, India. Capua would like to receive samples from as many countries as possible to enable her to create a global picture of what is happening.
Although some vaccinations have been developed against some variants of this disease, the big problem is that the virus changes very quickly and is therefore difficult for the birds’ immune systems to recognize.
Biosecurity and vaccinations are essential
Capua stressed that the role of wild birds in the spread of these diseases is becoming an increasing problem. She warned egg farmers that their hens’ immune systems will simply not be prepared for the new variations of these diseases. Strict biosecurity and appropriate vaccination strategies are essential for all egg operations.
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