The world is watching and waiting to see how Hong Kong manages its latest threat: the bird flu. But for us, the question this week is how to avoid getting the new virus, or, if the virus has already infected us, how to survive it. Knowing a little about the virus and how it spreads is the first weapon we need in our armoury. Thanks to some solid monitoring and investigation by the health authorities here and at the Centres for Diseases Control in the United States, we know the virus is a new type of influenza. It is described as an Influenza A(H5N1) virus because it has specific features able to react with our immune systems, known as antigens, which fit those categories. Knowing it is an influenza A virus is important, because that means it can be treated with a drug, Amantadine, which kills influenza A viruses, but not influenza B viruses. Possibly even more important is that this new virus has an H5 antigen. This is a tiny spike, visible only with an electron microscope, known as the 'H' agglutinin. Each time the flu virus evolves into a killer it undergoes what the virologists call 'antigenic shift', changing the H agglutinin into something the human immune system cannot easily recognise and destroy. By evolving a new agglutinin, the influenza virus effectively buys enough time to mount an overwhelming attack on our respiratory tracts before our immune defences can develop the right antibodies needed to neutralise the new strain. The influenza virus which killed between 20 and 40 million people during the 1919 pandemic of Spanish flu, had an H agglutinin named H1 by virologists. The next big killer, dubbed the Asian flu, which again killed millions in 1957 had changed its H agglutinin to what was labelled H2. And in 1968, when the Hong Kong flu swept the world, causing schools, business and services to grind to a halt while everyone was prostrated by the new strain, the new virus was found to have an H3 agglutinin. There were far fewer deaths in 1968 because another significant feature, the 'N' antigen was the same as the one found in the virus responsible for the 1957 pandemic. Although no one had exactly the right antibodies to fight off the virus in 1968, many people had antibodies close enough to give them a chance of surviving the virus. The bird flu virus found in the four cases in Hong Kong, has a new 'H' agglutinin, now identified as an H5. This means, should it change its genes enough to be able to spread itself from human to human, it could evolve into a virus able to kill on a grand scale. How it does this is an area in which Hong Kong has led the world. The University of Hong Kong's Professor of Microbiology, Professor Kennedy Shortridge, has been researching this throughout the 1970s and 80s, and his team has shown the flu virus is really meant to stay in birds as a bowel virus. Such viruses are found in ducks, chickens, and wild, migratory birds, but are supposed to be unable to infect humans. They lack the right antigens, or immune locators, needed to lock on to receptors in human throat cells and blast their way into our respiratory tracts, causing the sore throats, fevers, coughs and bronchitis familiar to anyone who has had the flu. While officially harmless to humans, new strains of bird flu are deadly to birds. A month before the first case in Hong Kong, a previously healthy three-year-old boy who died of flu complications last May, there was a severe outbreak which killed 70 per cent of the birds on three Yuen Long chicken farms. Two months before that an outbreak decimated the chicken population in a rural part of Guangdong. This bird virus is released into the environment through droppings from infected birds. These are often eaten by pigs, especially in southern China's crowded farmyards. Because pigs have receptors which are the same as human receptors, along with receptors similar to bird receptors, the pigs can get both human and bird flu strains. So, says Professor Shortridge, the pig is like a mixing vessel, allowing the bird virus to re-invent itself just enough to become a new human virus, different enough to outwit our immune systems. Professor Shortridge, along with the department of Agriculture and Fisheries are now sampling pigs and chickens to see if the virus is changing enough to cause a human pandemic. When the first boy died, investigators decided his infection was an isolated, unusual case. But with three more cases now appearing, within a few weeks of each other, the experts have to consider the possibility that the virus has become clever enough to skip the pig stage and go straight from birds to humans. That raises the question of whether or not this virus can attack all of us, or just people with the right immunological make-up to receive it. Professor Shortridge's studies in southern China suggest some farmers there get bird flu and do not even know it. While this debate may be fascinating for the experts, those at the coal-face, the people at risk of getting the disease and the doctors treating them, need to know, not whether they have bird, pig or human flu, but what to do about it. The best protection against the virus will be vaccination. It is expected the world's four flu vaccine production centres (at London, Atlanta, Melbourne and Tokyo) will start work on the vaccine in the next few weeks. But until then, our best weapons are prevention, early recognition of infection and specific treatment with Amantadine. Prevention involves two main strategies. First, all viruses can be neutralised by healthy immune systems. So keeping your immune system in optimum condition is your best chance of surviving infection. Immune systems function best when well supported with the right nutrients. Plenty of fresh food, especially fruit, vegetables, high fibre cereals and protein (from fish and meat) will provide your immune system with the best nutrition. Do not overcook, especially overboil, vegetables, because the trace elements your immune system needs will be lost. Along with good nutrition, immune systems need minimal stress. Lack of sleep, overworking and emotional stress have all been shown to damage immune systems. Overheating or underheating your body also stresses your immune system, so try to keep your environmental temperature stable. This means wearing plenty of warm clothes when outside (just as your grandmother always told you to), but also taking those wrappings off when you come indoors, especially into a heated building. Keeping your flat and office well-ventilated is another important preventive strategy. This means opening windows and letting air flow freely, so that if the virus is circulating it will be diluted or can even leave. This is easier said than done, given most of us work in buildings where the air-conditioning is centrally controlled but should still be thought about by those in charge of office environments. If, despite your best efforts you do get the virus, your best chance of complete recovery lies with early recognition of symptoms and treatment. The main difference between flu and a cold is the fever is higher (over 38 degrees) and often associated with aches and pains throughout the body, known as myalgia. Other than that the symptoms are generally a sore throat, runny nose, headaches, and, a little later, a cough. While health authorities do not usually advise running to the doctor with every cold, in this case, they hope people will seek advice early. General practitioners can take throat swabs if they suspect flu, then start treatment if necessary.