Virologists in Sao Paulo, Brazil, have identified a new strain of the influenza type A subtype H1N1 virus (colloquially referred to as swine flu), according to a June 16 announcement by the Instituto Adolfo Lutz. The mutated virus is related to the strain that caused a national health emergency in Mexico beginning in late April but does not appear to cause any more casualties than seasonal flu strains. Since the April flu outbreak, the virus has spread all over the world, prompting the World Health Organization to raise the pandemic alert for the virus to the highest level on June 11 (which indicates the spread of the virus, not its lethality). Although news of the virus mutation and the pandemic alert are alarming at first blush, at this point there is no clear cause for serious concern. The mutations reported by Brazil affect the character of the hemagglutinin proteins on the virus. Found on the outside of the virus in spike-like formations, hemagglutinin proteins put the "H" in H1N1 and are responsible for targeting host cells in an infected animal or individual. They are also the point of contact with immune systems, and are thus very important in determining whether or not the host body will recognize the virus as an intruder and put up a fight. There is always a chance that such a mutation could convert the virus into a more virulent form, and with the strain's already proven capacity to spread far and wide, such a mutation could cause serious damage. The 1918-1919 flu pandemic (frequently cited as a worst-case scenario) first manifested as a mild strain of the flu, but later mutated and spread around the world, causing millions of deaths. There is no evidence yet to suggest that this new virus is more effective or aggressive in targeting human hosts. The simple fact that the virus mutated should not necessarily ring alarm bells. Because of the harsh conditions faced by viruses in mammalian immune systems, there is enormous selective pressure that causes viruses to mutate rapidly to avoid destruction. Virus RNA is also less stable than the DNA used by most animals in the reproductive process, and during reproduction virus RNA is often copied with mistakes (mutations). The H1N1 virus can mutate — and is mutating. All viruses do. But that does not mean the world will necessarily face a deadly pandemic later in the year. Even if it does, the evidence of such a virulent mutation will not be seen in scientists' careful and painstaking genetic analysis; it will be indicated by an enormous and rapidly accruing number of casualties. It is simply impossible to predict which virus will make the leap to becoming a serious problem until after the leap has been made.