Human-to-Human Transmission Expected

Health authorities are investigating two possibilities for the transmission of the disease to the younger man: The first is that he contracted bird flu while attending to his sick brother. The second is that both men may have contracted it directly as a result of sharing a meal that included contaminated poultry.

All evidence to date suggests that isolated instances of limited, unsustained human-to-human transmission can be expected from avian influenza viruses in humans, according to WHO.

However, this does not warrant a heightened level of pandemic alert, says the organization. WHO points out that no other cases of respiratory illnesses have been identified among people who may have been in close contact with the two infected men in Tai Binh Province.

Raw Duck Blood, Organs Implicated

The possible direct source of disease transmission to the two men centers on a family meal that included a dish containing raw duck blood and organs.

Public health officials in Viet Nam repeatedly have warned against the consumption of dishes made with fresh duck blood or with raw or inadequately cooked poultry products, WHO points out. Residents of all countries experiencing outbreaks of H5N1 avian influenza in bird populations should avoid eating raw or undercooked poultry and egg products.

Contact with dead or diseased birds has been blamed for most human cases of bird flu to date. Humans are particularly vulnerable when slaughtering, defeathering and preparing poultry for cooking. WHO recommends that poultry should be cooked until all parts reach an internal temperature of 70 degrees Centigrade. No cases of H5N1 infection have been linked to the consumption of thoroughly cooked poultry and egg products, reports WHO.

Eight Cases in Viet Nam Since December

As of Friday, media reports that a third 35-year-old brother had been hospitalized were not confirmed, according to WHO.

These latest two cases bring the total in Viet Nam since mid-December 2004 to eight. Of these, seven have died. An 18-year-old woman from Tien Giang Province died on January 19.

Avian influenza is an infectious disease of birds caused by type A strains of the influenza virus. It was first identified in Italy more than 100 years ago, and is known to occur worldwide.

"Based on historical patterns, influenza pandemics can be expected to occur, on average, three to four times each century when new virus subtypes emerge and are readily transmitted from person to person," says a statement on the WHO Web site.

"However, the occurrence of influenza pandemics is unpredictable," the statement says. "In the 20th century, the great influenza pandemic of 1918-1919, which caused an estimated 40 to 50 million deaths worldwide, was followed by pandemics in 1957-1958 and 1968-1969. Experts agree that another influenza pandemic is inevitable and possibly imminent."