No Evidence of On-farm Circulation of Avian Influenza H5 Subtype in Ca Mau Province, Southern Vietnam, March 2016 – January 2017

Discussion The vast majority of Vietnam’s poultry sector is still smallholder poultry, with more than 96% of poultry-owning households holding fewer than 100 chickens15 and more than 93% of poultry-owning households holding fewer than 100 ducks16. Outbreaks of avian influenza on poultry farms are common and have been recorded every year in Vietnam1,17 since the re-emergence in 2002 and 2003 of highly-pathogenic avian influenza H5N1 genotypes in Asia18,19. Live poultry sales in Vietnam take place in a large informal system of household sales and wet markets, with some markets occupying the place of a central town/city market and others emerging temporarily on roadsides or in the countryside. Avian influenza viruses are detectable in markets, both in healthy and diseased birds, but contemporaneous sampling of healthy birds in markets and farms rarely shows any positive results on farms4. There is as yet no evidence that the virus can persist in market areas, and thus the more frequent direction of viral transmission is likely to be from farm to market. However, the informal nature of the sales, transportation, and storage chains has not been studied in enough detail to state with certainty that the virus cannot persist in market The logical mechanism of farm-to-market transmission would enjoy more evidential support if avian influenza viruses could be detected on farms at prevalence levels close to those at which they are observed in markets. A study aimed at gathering this...
Source: PLOS Currents Outbreaks - Category: Epidemiology Authors: Source Type: research