Health officials in Vietnam have identified two more people who have contracted the H5N1 bird flu virus. What is particularly alarming in these cases is that they appear to have contracted the virus from relatives who were also stricken. The two people had no other exposure to the disease other than through human-to-human contact.

Further, neither of these two people are showing any symptoms. This may be an indication that there are more people who actually have the virus than have presented with symptoms. If this is the case, the disease could be spreading silently.

One of those who tested positive for the flu is a 61-year-old woman who lost her husband to the disease. In an attempt to isolate the virus, health officials tested her chickens for the disease and found them to be unaffected.

The 81-year-old man who also tested positive for the disease has two grandchildren who contracted the flu. In this case, test on poultry have been inconclusive.

This development further solidifies concerns that the virus has begun to mutate and is already passing between humans. Earlier this week, a Vietnamese health care worker tested positive for the disease after having been exposed to patient with the virus. Then, on Tuesday, seven people who had tested negatively previously, were found to actually have the virus when tests were conducted in another lab.

The World Health Organization has been warning of the possibility of a pandemic should this virus begin to take hold in humans. These latest developments point out yet another concern - that of people who are positive for the virus, but present no symptoms. So far, no vaccine is available to combat this virus, and with further mutations probable, researchers are unable to predict the ultimate composition of the virus.