Here we go again. Just when we thought it was safe to go outside, the threat of another potential flu pandemic raises its head and hysteria builds again. Once again there is talk of quarantine, airport surveillance, travel restrictions and public closures.
The epidemic of a unique strain of swine flu raging in Mexico is suspected of causing more than 1600 cases of illness and about 150 deaths. It has affected at least 40 people in parts of the US as well as producing suspected cases in Britain, Canada, Spain, France, Colombia, Israel and Australia. In New Zealand some students from an Auckland secondary school who recently visited Mexico City also are suspected of having swine flu.
In a world where millions of people cross international borders by air every day, it appears that no one is safe. Flu recognises no international border constraints and moves at will.
In Mexico, universities, schools and public buildings have been closed, and in Mexico City authorities have been distributing free surgical face masks to commuters on the city's subway and buses. People have been urged to avoid public places and not to demonstrate any overt signs of affection, such as handshakes and kissing.
Air travellers are being screened for flu symptoms. Most of those affected have been young adults rather than the very young and the very old, the normal victims of flu outbreaks. Most of the deaths seem to be of people who sought medical attention at the last possible moment.
Are we confronting a re-run of the 1918-19 flu pandemic, when young, healthy adults bore the brunt of the outbreak? Most probably not, but the fear remains.
Although swine flu is known periodically to infect people, it has normally occurred where the virus has jumped to people directly exposed to animals, such as pig farmers. Remember bird flu? Much the same applied, where people living cheek by jowl (feather?) with poultry were the most at risk.
The latest virus is a new strain not previously encountered in animals or humans. Disturbingly, it seems to combine bird, swine and human viruses in a manner not seen before, and is spreading from person to person.
Pigs are wonderful mixing vessels for respiratory viruses and this time they seem to have really stirred things up. There is no specific vaccine for this strain and it remains unclear how useful contemporary human flu vaccines will be in offering protection, although the virus seems sensitive to the drugs Tamiflu and Relenza.
Swine flu has a long and interesting history. While there is no record of it causing a human flu pandemic, this latest outbreak stirs memories of the 1976 public health debacle in the US when 200 soldiers at Fort Dix in New Jersey and Fort Meade in Maryland fell ill with what turned out to be swine flu, causing a wave of panic to spread through the community and public health authorities.
In response the US government began a nationwide vaccination campaign. When a pandemic never eventuated the program was halted, but not before hundreds of people had developed Guillain-Barre syndrome as a result of vaccination, including at least 33 deaths. It seems that even when we act with the best intentions we can unwittingly cause human tragedy.
If nothing else, this outbreak demonstrates how easily human perception and reaction can transform an epizootic (animal epidemic) or a localised human outbreak into something resembling human Armageddon.
Remember severe acute respiratory syndrome and bird flu? We seem destined to relive repeatedly our epidemiological past, and what we always seem to get is two epidemics, not one.
The first is an epizootic or a human epidemic. The second is often an extraordinary epidemic of fear, hysteria and panic, partly orchestrated by government and media comments about how much our health and wellbeing is threatened.
That said, public health authorities have long been concerned about the emergence of a new flu virus that may launch a global pandemic. Flu viruses mutate regularly and easily, and we always seem to be one step behind: reacting rather than anticipating.
There is little doubt that we are long overdue for another flu pandemic. It is 40 years since the last flu pandemic and history suggests that some time in the next few years we will experience another.
The emergence of infections such as SARS, bird flu and swine flu underscores that mutation and change are facts of life, that microbes change in accord with alterations in their environment and in their host, and that our health is often a delicate balance between people, wild and domestic animals, and the microbial world.
Peter Curson is professor of population and security at the Centre for International Security Studies, University of Sydney, and emeritus professor of medical geography at Macquarie University, Sydney.
Contact: Jacob O'Shaughnessy