Vietnam: Global Overview-January 2010-Prepared by EMPRES/FAO GLEWS

Excerpts:

The question still remains as to where the virus hides during inter-epidemic periods in the complex and variable poultry production systems comprising chickens, ducks and rice fields. Consistent outbreak investigations are not undertaken on infected farms and key information is usually missing from the field.

In January 2010, a human case was observed in a 3-year old female from Khanh Hoa Province. The source of exposure is under investigation. Her family raises chickens but did not report any mass poultry illness or death.

Based on the monitoring of surveillance activities, three currently circulating virus clades have been isolated: (1) HA Clade 1 (predominant in southern Viet Nam and also isolated in Cambodia); (2) HA Clade 2.3.4 (predominant in northern Viet Nam and also circulating in China); and (3) HA Clade 7 (detected in poultry seized at the Chinese border and at markets near Hanoi). In 2009, ten viruses were sent to the U.S. Centers for Disease Control and Prevention (CDC) for sequencing and, to date, no new circulating clade has been detected.
A recent study by Carrel et al. (2010) showed that there have been at least six independent H5N1 introductions into Viet Nam and there were nine newly emerged reassortants from 2001 to 2007. H5N1 viruses in Viet Nam cluster distinctly around Hanoi and Ho Chi Minh City. More information is available at…

From: http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0008631:
While the interactions between time, space and genetic evolution could potentially be circumvented by repeated introductions of H5N1 strains of different lineages into Vietnam, we would still expect to see the northern region around Hanoi and the southern region around Ho Chi Minh City acting as important sites of genetic differentiation rather than the central region of the country.

Genetic distance between case pairs is higher in 2005 and 2007 than in the first two years of the dataset, an indication that these influenza viruses have evolved as local epidemic strains in domestic poultry after sweeping over Vietnam during the 2003–2004 outbreaks.

By 2007, however, genetic distances are similar for the within- and between-region categories. The significant three-way interaction (Table 1) indicates that genetic variation in Vietnamese HK821-like cases is systematically different between regions, years and gene segments, and that these three factors interact in ways that affect genetic distances between virus case pairs.