The role of vaccines and vaccination in high pathogenicity avian influenza control and eradication.

Thirty epizootics of high pathogenicity avian influenza (HPAI) or fowl plague have occurred in poultry and other birds in the world since influenza virus was discovered to be the etiological agent of the disease in 1955 [1]. The largest epizootic of the past 50 years was the H5N1 panzootic, which began in the Guangdong province of southern China in 1996 and has since spread to affect 63 countries, resulting in the death or culling of over 250 million poultry and wild birds. Twenty four epizootics were eradicated using a fourcomponent stamping-out strategy that included education, biosecurity, rapid diagnostics and surveillance, and elimination of infected birds. However, the inability of the stamping-out strategy to eradicate H5N2 HPAI in Mexico and H7N3 HPAI in Pakistan during 1994–1995 challenged the dogma of immediate eradication being achievable under all national political structures, poultry production systems, economic conditions and HPAI outbreak situations using traditional eradication methods [2]. Therefore, Mexico and Pakistan initiated the use of a fifth control component, increasing resistance of poultry to HPAI viruses by vaccination, which had been used previously to control low pathogenicity avian influenza (AI) in the USA and Italy [3–6]. More recently, vaccines for HPAI control have been utilized in the Democratic People’s Republic of Korea against H7N7 HPAI (2005) and in 13 of the 63 countries affected with H5N1 HPAI (1996 to present) [2]. Although the H5N1 HPAI panzootic continues, the H5N2 Mexican, H7N3 Pakistani and H7N7 Korean HPAI epizootics have ended. The recent Chinese Taipei (H5N2; 2012) and South African (H5N2; 2011) epizootics are nearing eradication using stamping-out programs only. The ability to eradicate HPAI is inf luenced by the competency of the governmenta l veterinary medica l authority, the density of poultry within the country and the level of governmental participation [7,8]. The eradication of H5N1 HPAI has been more complex than the other 29 HPAI epizootics because it has involved multiple countries, affected more diverse types of poultry production systems, infected wild birds and had a major public health element. The latter aspect has involved 607 hospitalized cases with 358 deaths, and the H5N1 HPAI virus has the potential to become a future pandemic virus [101]. This public health aspect resulted in mobilization of a global effort to eradicate H5N1 HPAI from poultry, but the veterinary infrastructure and finances have not been adequate to conduct an effective stamping-out campaign in all countries [8]. Therefore, vaccination was administered in order to decrease bird susceptibility to infection, The role of vaccines and vaccination in high pathogenicity avian influenza control and eradication