You may have recently been hearing about “bird flu”, but do you know what is it? Many people don’t . Basically, the influenza virus comes in three general varieties; A, B and C. These reflect differences in the M protein on the envelope that contains the virus. The A influenza viruses are the ones that cause both human and bird flu outbreaks.

Type A influenza viruses are sub-typed based on two different kinds of activity within their envelope’s glycoproteins. The first is hemagglutinnin activity, designated H. There are 16 known varieties of this. The second is neuraminidase activity, designed N, with nine known varieties. The shorthand code names of both bird and human flu always have an “H” and “N” number. For example, the 1918 Spanish flu pandemic was caused by H1N1.

The influenza A virus appears most in wild bird populations, spreading rapidly through exchange of mucus or feces, and generally without creating sickness or death in these species2. However, once it transfers over to domestic birds, including chickens, ducks and turkeys, it spreads explosively and is frequently lethal.

The H5N1 bird flu has infected humans and continues, as we speak, to evolve6. It was first identified in South African wild terns in 1961. 2 It spread naturally throughout global bird populations over the next four decades, appearing dramatically in pultry populations in 2003. That outbreak occured in eight countries in Asia – Cambodia, China, Indonesia, Japan, Laos, South Korea, Thailand and Vietnam – and resulted in the loss of more than 100 million domestic birds. The outbreak appeared under control until June of 2004 when it reappeared in four of the same countries and Malaysia.

In humans, the appearance was less dramatic. H5N1 first infected a human population in Hong Kong in 1997. There were 18 documented cases and six deaths. It reappeared in 2 cases, causing one death in 2003, but shortly thereafter broke out in Vietnam, Thailand and Cambodia. As of June 2005, there were 100 documented human cases with 54 percent mortality rate. Most transmission has been the result of direct contact with infected poultry.

But 100 deaths does not pandemic make. You need three things for a pandemic. First, a highly virulent organism. Second, lack of human immunity to the organism, and Third, the ability for easy transmission from human to human. In 1918, H1N1 had all three. That’s why 20 to 40 million people died. In 2005, N5H1 has the first two, but not the third – at least not yet.

Out current capacity to diagnose and manage an H5N1 pandemic is less than adequate. To prevail, we need excellent surveillance that relies on clinical, scientific and technologic capacity. We need knowledge sharing and the will to act, and act quickly, at the first signs of facilitated human-to-human transmission.

The cautioned, however, that the existence of a vaccine in itself would not be enough to prevent a worldwide pandemic. They said more testing must be done before the vaccine can be offered to the public, and production could be stumbling block.