Highly pathogenic avian influenza A (H5N1) virus in wildlife: diagnostics, epidemiology and molecular characteristics

Abstract

Since 2003, highly pathogenic avian influenza virus subtype H5N1 outbreaks have been reported in Southeast Asia causing high mortality in poultry and have also been found to cross the species barrier infecting human and other mammalian species. Thailand is one of the countries severely affected by the HPAI H5N1 outbreaks. After the first fatal HPAI H5N1 infections were reported in tigers and leopards that had been fed carcasses of infected chickens in a zoo in Thailand, the viruses involved were characterized and studies about the pathogenesis of the disease in these large felids were performed. Since July 2005, HPAI H5N1 viruses have also been detected in Europe and Africa. Migratory birds were suspected to have carried and spread these viruses from Asia. By experimentally infecting wild ducks, tufted ducks, Eurasian pochards, and mallards excreted significantly more virus than common teals, Eurasian wigeons, and gadwalls; yet only tufted ducks and, to a lesser degree, pochards became ill or died. These findings suggest that some wild duck species, particularly mallards, can potentially be long-distance vectors of HPAI H5N1 and that others, particularly tufted ducks, are more likely to act as sentinels. Surveillance studies performed during HPAI H5N1 epidemics in Thailand from 2004 to 2007 provided important epidemiological data. A retrospective analysis was performed to study spatial distribution, temporal analysis and the relationship associated between H5N1 virus outbreaks in poultry flocks and wild birds using a non-homogeneous birth and death statistical model. Transmission efficiency among poultry flocks was 1.7 times higher, in regions with infected wild birds in the given or preceding month. Presence of wild birds may contribute consistently to the spread of HPAI H5N1 virus among poultry flocks. During the widespread outbreaks in Thailand, H5N1 viruses also caused clinical signs and mortality in many of wild birds species. To study the phylogenetic relationship between the HPAI H5N1 virus isolates from poultry and wild birds, a molecular characterization study of the HA and NA genes was carried out to reveal any differences between strains found in different host species. To control pandemic influenza A virus outbreaks, vaccination is a recommended and often effective strategy. A database and repository of the recombinant viruses that can be used for vaccine production, diagnostic and research purposes would be extremely valuable for this purpose. To this end, recombinant influenza A viruses, containing one of the 16 HA subtypes and one of the nine NA subtypes of the Eurasian lineages were produced in a A/PR/8/34 backbone using reverse genetic techniques. The outbreak of HPAI H5N1 causes disease and fatality among avian and mammalian species. As the establishing the diagnosis still constitutes a major challenge, there is a need for adequate information on the possibilities to diagnose the disease in diseased and dead animals. A comprehensive overview was made of HPAI H5N1 virus induced clinical signs and pathology from both natural and experimental studies in different animals and was to provide a practical guide for collecting the appropriate samples to establish the diagnosis HPAI H5N1 in these animals.