HANOI, Dec 21 (Reuters) - Vietnam's first outbreak of bird flu since August has spread to four more areas in the Mekong Delta, where nearly 8,300 birds have been killed by the virus or slaughtered to hold it back, the Agriculture Ministry said. Three outbreaks spotted between Dec. 11 and Dec. 20 in Ca Mau province killed over 2,500 chickens and ducks, while one in neighbouring Bac Lieu province killed dozens of ducks, the ministry's Animal Health Department said in a report on Thursday. The outbreaks of the H5N1 virus were the first in Vietnam since August. The initial eruptions killed around 6,000 newly hatched chickens and ducklings that were not vaccinated against bird flu. Farmers have since thrown dead birds into water channels or let ducks roam on rice fields, helping spread the virus that first arrived in the Delta in late 2003 and has since killed 42 of the 93 people infected in Vietnam. Vietnam, which has had no human bird flu cases since late 2005, has a human death toll second only to Indonesia's 57, according to the World Health Organisation (WHO). WHO says bird flu has killed 154 people out of 258 infected globally since late 2003. Vietnamese animal health officials said on Wednesday that temperatures were falling in the southern region incorporating the delta, which would help the spread of a virus that thrives best in cooler temperatures. Experts fear the virus could mutate into a form that is easily transmissible among humans and spark an influenza pandemic that would kill millions. The Mekong Delta outbreaks caused health officials in nearby Ho Chi Minh City, Vietnam's largest city, to tighten inspection of poultry and step up monitoring of breeding farms, state media reported on Thursday.
