Abstract
Highly pathogenic avian influenza (HPAI) virus H5N1 is now endemic in South-East Asia but HPAI control methods differ between countries. A widespread HPAI vaccination campaign that started at the end of 2005 in Viet Nam resulted in the cessation of poultry and human cases, but in 2006/2007 severe HPAI outbreaks re-emerged. In this study we investigated the pattern of this first post-vaccination epidemic in southern Viet Nam identifying a spatio-temporal cluster of outbreak occurrence and estimating spatially smoothed incidence rates of HPAI. Spatial risk factors associated with HPAI occurrence were identified. Medium-level poultry density resulted in an increased outbreak risk (Odds ratio (OR) = 5.4, 95% confidence interval (CI): 1.6–18.9) but also climate-vegetation factors played an important role: medium-level normalised difference vegetation indices during the rainy season from May to October were associated with higher risk of HPAI outbreaks (OR = 3.7, 95% CI: 1.7–8.1), probably because temporal flooding might have provided suitable conditions for the re-emergence of HPAI by expanding the virus distribution in the environment and by enlarging areas of possible contacts between domestic waterfowl and wild birds. On the other hand, several agricultural production factors, such as sweet potatoes yield, increased buffalo density, as well as increased electricity supply were associated with decreased risk of HPAI outbreaks. This illustrates that preventive control measures for HPAI should include a promotion of low-risk agricultural management practices as well as improvement of the infrastructure in village households. Improved HPAI vaccination efforts and coverage should focus on medium poultry density areas and on the pre-monsoon time period.
Highlights
Pathogenic avian influenza (HPAI) H5N1 has affected many millions of poultry producers and their families in South-East Asia for more than a decade
We used three data sources to summarize all reported Highly pathogenic avian influenza (HPAI) outbreaks from the end of 2006 to the beginning of 2007: (1) outbreaks officially reported to the World Organisation of Animal Health (OIE)1, (2) data published on the Department of Animal Health (DAH) website2 and (3) a small set of data from farm-level outbreak investigations conducted by an
In December 2006, HPAI H5N1 outbreaks were reported on poultry farms in three southern Vietnamese provinces followed by four more provinces in January 2007
Summary
Pathogenic avian influenza (HPAI) H5N1 has affected many millions of poultry producers and their families in South-East Asia for more than a decade. HPAI had been successfully controlled in Hong Kong and Thailand by Article published by EDP Sciences. An intensive vaccination program initiated in 2005 provided lessons to the international community on how the disease can be successfully controlled. No outbreaks occurred almost over an entire year. Reemergence of H5N1 began in December 2006 in the Ca Mau province of Southern Viet Nam spreading quickly to other provinces in the region. No human cases were reported as a result of these outbreaks [8]
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