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Key Points on Bird Flu Control Outlined at WVPA Meeting

21 December 2011, at 12:00am

Avian influenza viruses have been and remain important public and animal health due to economic and human fatalities that cause, according to Dr Alejandro Garcia of Laboratorios Avilab in Mexico. Chris Wright, senior editor of ThePoultrySite, reports.


Dr Alejandro Garcia

Dr Alejandro Garcia of Laboratorios Avilab in Mexico shared his experience of avian influenza with delegates during the XVII Congress of the World Veterinary Poultry Association (WVPA), held in Cancun, Mexico in August 2011.

The Avian Influenza virus (AIV) is an animal disease; veterinarians and vet scientists play an important role in the management in preventing humans coming into contact with the disease.

We must resolve the problem of the carriers (wild and migrating birds) because they mobilise the virus, putting at risk commercial animals, said Dr Garcia. The control and prevention of them are essential in avoiding a possible human pandemic.

Control and Eradication of Avian Influenza

The best action for a country, zone or compartment in the control and prevention of AIV is the total eradication by slaughter of diseased animals' destruction of carcasses and all the elements related to infected birds (bedding, feed etc.), said Dr Garcia.

Washing and disinfection of the barns and contaminated material according to the standards specified by the OIE in its Code of Animal Health Land, is another of the practices to be implemented.

In some countries, the characteristics of the poultry industry and the circumstances under which there have been outbreaks and epidemics caused by viruses of high and low pathogenicity AI, force the use of vaccination.

Vaccination is a useful tool for the control of avian influenza (AI) outbreaks, continued Dr Garcia, but its use is forbidden in most countries worldwide because of its interference with AI screening tests and its negative impact on poultry trade.

Currently licensed AI vaccines increase host resistance to the disease but have a limited impact on the virus transmission, he said. To control or eradicate the disease, a carefully conceived vaccination strategy must be accompanied by strict biosecurity measure.

Recently, the World Organisation for Animal Health (OIE) and the United Nation's Food and Agricultural Organization (FAO) have recommended the use of vaccination against H5N1 HPAI virus in developing countries where mass culling of poultry is no longer acceptable for ethical, cultural, ecological and economic reasons.

Conclusions About Avian Influenza

Based on the author's extensive knowledge of avian influenza and its effects on the poultry industry, Dr Garcia offered 21 important observations about the disease.

1. AIVs have been and remain important for public and animal health due to the economic and human fatalities they cause.

2. AIV, by its genetic nature, has the ability to mutate very quickly, producing viruses that are mostly new to the immunological memory of the human or animal populations. This feature of the virus also generated highly pathogenic virus from one that had originally been of low pathogenicity.

3. AI is a very dangerous virus and is capable of changing its life cycle – either by glycosylation, deletion, insertion or substitution events, some amino acids in different proteins in their genomes etc. – when it is under pressure from the animal's immune system. It does so in order to survive.

4. The role of migratory birds is still inconclusive in the spread and occurrence of the disease in affected countries.

5. The presence of the disease in poultry populations is determined primarily by discrete biosecurity measures and management of products and subproducts, as poultry flocks are free of the disease are found in areas where the virus is endemic.

6. AIV subtype H5 or H7 has killed humans of all ages from young children to adults.

7. It is known that H5N1 has the capacity to be transmitted occasionally from human to human. Such transmission, however, has only occurred in exceptional instances, usually involving very close contact with a patient during the acute phase of illness. To date, H5N1 has not spread beyond one generation of close contacts.

8. The risk of transmission and adaptation of AIVs from animals to humans and the increase in mortality is low, e.g. Asian H5N1, H1N1 North America. This is related to the cell receptors that have each species in their epithelial cells of the virus target organs.

9. Vaccination has helped to mitigate the disease in the poultry population and reduced the number of deaths in humans.

10. There are areas in developing countries, which lack electricity and have AI vaccines of poor efficiacy, where it is difficult to control the disease in poultry populations.

11. Different degrees of protection and immune responses have been observed in some avian species, e.g. chickens versus waterfowl or gulls and ducks, that have been vaccinated with inactivated emulsified AI vaccine.

12. Maternal antibodies influence the response to the vaccine. In some cases, the antibodies completely block the response, leaving the poultry susceptible to disease.

13. The smuggling of live or dead animals as well as products and by-products of poultry, may be the most important source of spread of a disease-free country – more than the presence of migratory birds.

14. Live bird markets represent an ideal environment for the transmission, survival and crossing of the virus.

15. When statutory notifiable avian disease is confirmed, action to confine and stamp out disease includes movement controls on susceptible species in the area around the premises, enhanced biosecurity, culling of susceptible poultry on the farm, and cleansing and disinfection of the premises.

16. The elimination of highly pathogenic virus either H5 or H7 subtype in poultry flocks can be achieved as long as affected and exposed birds are slaughtered and movement of poultry products and by-products is strictly controlled. Epidemiological surveillance and biosecurity are also required.

17. The measures taken by developing and underdeveloped countries to free poultry flocks from the disease are dramatically different and depend on the level of financial support (compensation), the first countries, affected birds slaughtered, the suspect and the adjacent, coupled with strict biosecurity measures and movement of poultry products and by-products, which have to comply with health campaigns, immunisation and different levels of biosecurity measures.

18. Timely notification of AI virus and transparency of governments and people involved in the poultry-animal interface help to control and possibly eradicate the disease.

19. AIVs emerge and re-emerge: for example, in the Netherlands, subtype H7N1 from 2010 re-emerged in March 2011.

20. The press and other media (TV, radio, internet, etc) and some academics have been responsible for magnifying and sometimes exaggerating the pathogenicity of the virus. This has affected the productive sectors (animals) and the economy of a country, said Dr Garcia. He cited the example of Mexico in 2009, when H1N1 swine flu, which is then considered a pandemic. A year later, the title 'pandemic' was dropped but not before the sector was severely damaged. It is known that there were pressures to classify this virus as pandemic in 2009.

21. The presentation of pandemic or epizootic of any subtype of the AIV is difficult, concluded Dr Garcia. Protection involves not only humoral immunity but also cellular and innate forms and there is also cross-protection between some subtypes, e.g. between H9N2 and H5N1, as they share some peptide homology along the HA protein.

Further Reading

- You can visit the Avian Flu page by clicking here.


December 2011