ARS | Publication request: Surveillance for highly pathogenic avian influenza virus among wild birds in Mongolia, 2005-2011

Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 30, 2012
Publication Date: September 11, 2012
Citation: Gilbert, M., Jambal, L., Karesh, W., Dulam, P., Sodnomdarjaa, R., Tseveemyadag, N., Cardona, C., Leung, C., Peirs, M., Spackman, E., Swayne, D.E., Joly, D. 2012. Surveillance for highly pathogenic avian influenza virus among wild birds in Mongolia, 2005-2011. PLoS One. 7(9):e44097.

Interpretive Summary: Severe forms of avian influenza virus (AIV) called highly pathogenic (HP) have persisted in wild birds in Asia since the mid-2000’s. The ecology of the virus in wild birds is not well understood because infected birds are normally found near infected poultry, therefore poultry often plays an important role for the spread of HP AIV in wild birds. Mongolia is a country with little poultry production, most of which is centralized in urban areas. Mongolia is also positioned geographically in an area which serves as a major migratory fly-way for numerous wild bird species. Therefore Mongolia is an ideal location to conduct studies on the HP AIV endemic in Asia and the role of wild birds. In this report a six year study from 2005-2011 was conducted in numerous rural areas of Mongolia to monitor wild birds for HP AIV. Only eight positive samples in 2005 or 2010 were discovered after testing thousands of samples. The positive samples from 2005 were genetically distinct from the samples from 2010. These rare positive samples suggest that the HP AIV which is now entrenched in poultry is not stably maintained in wild birds in the region.

Technical Abstract: The central Asian country of Mongolia supports large populations of migratory water birds that migrate across much of Asia where highly pathogenic avian influenza (HPAI) virus subtype H5N1 is endemic. This, together with the near absence of domestic poultry, makes Mongolia an ideal location to understand the epidemiology of HPAI H5N1 in a purely wild system. Here we present the findings of active and passive surveillance for HPAI H5N1 in Mongolia from 2005-2011, together with the results of five outbreak investigations. In total eight HPAI outbreaks were confirmed nationally during this period, with a further three reported in the neighboring Tyva Republic on a lake that bisects the international border. Only one outbreak was identified through active surveillance implemented through this project, with four detected through passive surveillance systems, and three by active surveillance implemented by government. No HPAI virus was isolated from 7,855 environmental fecal samples, or from 2,817 live clinically healthy birds captured during active surveillance, while four HPAI viruses were identified in samples collected from 145 sick or dead birds located through active surveillance. All Mongolian outbreaks occurred in 2005 and 2006 (clade 2.2), or 2009 and 2010 (clade 2.3.2.1); all years with spring outbreaks reported in Tibet and Qinghai provinces in China. Outbreaks followed a marked temporal and spatial pattern of occurrence, with three of four May outbreaks occurring in the north-central region, all Tyvan outbreaks in early June, and all four late July outbreaks in the north-central region. Biotic and abiotic features of outbreak lakes may partially explain this pattern and are discussed. The occurrence of outbreaks in areas deficient in domestic poultry is strong evidence that wild birds can carry HPAI over at least moderate distances. However, failure to detect further outbreaks of clade 2.2 after June 2006, and clade 2.3.2.1 after June 2010 suggests that Mongolian wild birds are not competent as indefinite reservoirs of infection.