Avian influenza outbreak management: action at time of confirmation, depopulation and disposal methods; the 'Belgian experience' during the H7N7 highly pathogenic avian influenza epidemic in 2003

The significance of avian influenza virus mouse-adaptation and its application in characterizing the efficacy of new vaccines and therapeutic agents

Due to the increased frequency of interspecies transmission of avian influenza viruses, studies designed to identify the molecular determinants that could lead to an expansion of the host range have been increased. A variety of mouse-based mammalian-adaptation studies of avian influenza viruses have provided insight into the genetic alterations of various avian influenza subtypes that may contribute to the generation of a pandemic virus. To date, the studies have focused on avian influenza subtypes H5, H6, H7, H9, and H10 which have recently caused human infection. Although mice cannot fully reflect the course of human infection with avian influenza, these mouse studies can be a useful method for investigating potential mammalian adaptive markers against newly emerging avian influenza viruses. In addition, due to the lack of appropriate vaccines against the diverse emerging influenza viruses, the generation of mouse-adapted lethal variants could contribute to the development of effective vaccines or therapeutic agents. Within this review, we will summarize studies that have demonstrated adaptations of avian influenza viruses that result in an altered pathogenicity in mice which may suggest the potential application of mouse-lethal strains in the development of influenza vaccines and/or therapeutics in preclinical studies.

Prevalence and control of H7 avian influenza viruses in birds and humans

The H7 subtype HA gene has been found in combination with all nine NA subtype genes. Most exhibit low pathogenicity and only rarely high pathogenicity in poultry (and humans). During the past few years infections of poultry and humans with H7 subtypes have increased markedly. This review summarizes the emergence of avian influenza virus H7 subtypes in birds and humans, and the possibilities of its control in poultry. All H7Nx combinations were reported from wild birds, the natural reservoir of the virus. Geographically, the most prevalent subtype is H7N7, which is endemic in wild birds in Europe and was frequently reported in domestic poultry, whereas subtype H7N3 is mostly isolated from the Americas. In humans, mild to fatal infections were caused by subtypes H7N2, H7N3, H7N7 and H7N9. While infections of humans have been associated mostly with exposure to domestic poultry, infections of poultry have been linked to wild birds or live-bird markets. Generally, depopulation of infected poultry was the main control tool; however, inactivated vaccines were also used. In contrast to recent cases caused by subtype H7N9, human infections were usually self-limiting and rarely required antiviral medication. Close genetic and antigenic relatedness of H7 viruses of different origins may be helpful in development of universal vaccines and diagnostics for both animals and humans. Due to the wide spread of H7 viruses and their zoonotic importance more research is required to better understand the epidemiology, pathobiology and virulence determinants of these viruses and to develop improved control tools.

Molecular epidemiological analysis of the transboundary transmission of 2003 highly pathogenic avian influenza H7N7 outbreaks between the Netherlands and Belgium

The 2003 outbreak of Highly pathogenic avian influenza (HPAI) A(H7N7) in the Netherlands, Belgium and Germany resulted in significant genetic diversification that proved informative for tracing transmission events. Building on previous investigations on the Dutch outbreak, we focused on the potential transnational transmissions between the Netherlands and Belgium. Although no clear epidemiological links could be identified from the tracing data, the transmission network based on concatenated HA-NA-PB2 sequences supports at least three independent introductions from the Netherlands to Belgium and suggests one possible introduction form Belgium back to the Netherlands. Two introductions in the Belgian province of Limburg occurred from nearby farms in the Dutch province of Limburg. One introduction resulted in three secondary infected farms, while a second introduction did not cause secondary infections. The third introduction into Belgium occurred in the north of the Antwerp province, very close to the national border, and originated from the North of the Dutch province Brabant (long distance transmission, >65 km). The virus spread to two additional Belgian farms, one of which may be the source of a secondarily infected farm in the Netherlands. One infected turkey farm in the province of Antwerp (Westmalle) was geographically close to the latter introduction, but genetically clustered with the first introduction event in the Limburg province. Epidemiological tracing data could neither confirm nor exclude whether this outbreak was a result from long distance contacts within Belgium or whether this farm presented a fourth independent transboundary introduction. These multiple transnational transmissions of HPAI in spite of reinforced biosecurity measures and trade restrictions illustrate the importance of international cooperation, legislation and standardization of tools to combat transboundary diseases.

Genetic data from avian influenza and avian paramyxoviruses generated by the European network of excellence (EPIZONE) between 2006 and 2011--review and recommendations for surveillance

Since 2006, the members of the molecular epidemiological working group of the European "EPIZONE" network of excellence have been generating sequence data on avian influenza and avian paramyxoviruses from both European and African sources in an attempt to more fully understand the circulation and impact of these viruses. This review presents a timely update on the epidemiological situation of these viruses based on sequence data generated during the lifetime of this project in addition to data produced by other groups during the same period. Based on this information and putting it all into a European context, recommendations for continued surveillance of these important viruses within Europe are presented.

Comparative analysis of avian influenza virus diversity in poultry and humans during a highly pathogenic avian influenza A (H7N7) virus outbreak

Although increasing data have become available that link human adaptation with specific molecular changes in nonhuman influenza viruses, the molecular changes of these viruses during a large highly pathogenic avian influenza virus (HPAI) outbreak in poultry along with avian-to-human transmission have never been documented. By comprehensive virologic analysis of combined veterinary and human samples obtained during a large HPAI A (H7N7) outbreak in the Netherlands in 2003, we mapped the acquisition of human adaptation markers to identify the public health risk associated with an HPAI outbreak in poultry. Full-length hemagglutinin (HA), neuraminidase (NA), and PB2 sequencing of A (H7N7) viruses obtained from 45 human cases showed amino acid variations at different codons in HA (n=20), NA (n=23), and PB2 (n=23). Identification of the avian sources of human virus infections based on 232 farm sequences demonstrated that for each gene about 50% of the variation was already present in poultry. Polygenic accumulation and farm-to-farm spread of known virulence and human adaptation markers in A (H7N7) virus-infected poultry occurred prior to farm-to-human transmission. These include the independent emergence of HA A143T mutants, accumulation of four NA mutations, and farm-to-farm spread of virus variants harboring mammalian host determinants D701N and S714I in PB2. This implies that HPAI viruses with pandemic potential can emerge directly from poultry. Since the public health risk of an avian influenza virus outbreak in poultry can rapidly change, we recommend virologic monitoring for human adaptation markers among poultry as well as among humans during the course of an outbreak in poultry.

A quantitative assessment of the risk for highly pathogenic avian influenza introduction into Spain via legal trade of live poultry

Highly pathogenic avian influenza (HPAI) is considered one of the most important diseases of poultry. During the last 9 years, HPAI epidemics have been reported in Asia, the Americas, Africa, and in 18 countries of the European Union (EU). For that reason, it is possible that the risk for HPAI virus (HPAIV) introduction into Spain may have recently increased. Because of the EU free-trade policy and because legal trade of live poultry was considered an important route for HPAI spread in certain regions of the world, there are fears that Spain may become HPAIV-infected as a consequence of the legal introduction of live poultry. However, no quantitative assessment of the risk for HPAIV introduction into Spain or into any other EU member state via the trade of poultry has been published in the peer-reviewed literature. This article presents the results of the first quantitative assessment of the risk for HPAIV introduction into a free country via legal trade of live poultry, along with estimates of the geographical variation of the risk and of the relative contribution of exporting countries and susceptible poultry species to the risk. The annual mean risk for HPAI introduction into Spain was estimated to be as low as 1.36 x 10(-3), suggesting that under prevailing conditions, introduction of HPAIV into Spain through the trade of live poultry is unlikely to occur. Moreover, these results support the hypothesis that legal trade of live poultry does not impose a significant risk for the spread of HPAI into EU member states.

Avian influenza: the tip of the iceberg

For some years now, we have been living with the fear of an impending pandemic of avian influenza (AI). Despite the recognition, in 1996, of the global threat posed by the highly pathogenic H5N1 influenza virus found in farmed geese in Guangdong Province, China, planning for the anticipated epidemic remains woefully inadequate; this is especially true in developing countries such as Saudi Arabia. These deficiencies became obvious in 1997, with the outbreak of AI in the live animal markets in Hong Kong that led to the transmission of infection to 18 humans with close contact with diseased birds; there were six reported deaths. In 2003, with the reemergence of H5N1 (considered the most likely AI virus) in the Republic of Korea and its subsequent spread to Thailand, Vietnam, Hong Kong and China. Many countries started aggressively making preparations to meet the threat. The pressure for real action from governments has increased. Most developed countries have requested increased funding for the search for a more effective vaccine, for stockpiling possibly helpful antiviral drugs, and for intensifying domestic and global surveillance. Most countries, however, continue to be inadequately prepared for such an epidemic, especially with regard to animal surveillance in the farm market and surveillance among migratory birds. Even now, most countries do not have the ability to detect disease among humans in the early stages of an outbreak nor do most hospitals comply with effective infection control measures that could curtail the spread of the virus in the early stages of an epidemic. In Saudi Arabia we are rapidly implementing many of these measures.