According to the the World Health Organization (WHO), the pattern of human bird flu infections in Vietnam suggests the H5N1 virus that causes the illness is evolving in ways that makes it more contagious.
Vietnam, the nation hit hardest by the disease, has recorded 68 cases of bird flu in humans between late 2003 and the end of April. Two more human cases have been recorded since then by Vietnamese health authorities, though not yet confirmed by the United Nations health agency. At least 36 Vietnamese have died after contracting the H5N1 bird-flu virus.
In a review of bird-flu cases, the WHO says a wider age range of people are being infected but there are fewer deaths from the disease, and it is possible that the changes demonstrate that H5N1 viruses are becoming more capable of human-to-human transmission.
The WHO says the avian H5N1 viruses are continuing to evolve and pose a potential pandemic threat, and it is possible that the viruses are becoming more infectious for people.There are however some epidemiological differences between the two outbreaks reported since the end of last year.
Vietnamese health authorities have this year reported cases in a health-care worker and in at least four sets of family members, and investigators are concerned that change in the pattern of the disease raises the possibility that transmission between humans has occurred.
Three asymptomatic infections were documented among close contacts of confirmed cases, suggesting the presence of milder degrees of infection.