The H5N1 flu virus has now been reported from most of the world and will surely spread further as wild migratory birds are also involved. Human cases have, so far, been almost exclusively among persons who had close contact with chickens and ducks. Human to human transmissions have been extremely rare. Birds harbor the virus in respiratory excretions and feces. There is as yet no human vaccine for H5N1 virus and the human influenza vaccines are ineffective against this virus. Travelers should avoid contact with birds, should not visit fresh markets where animals are sold and should not go near chicken or duck farms. Eating well cooked chickens and ducks is safe.
Severe acute respiratory syndrome (SARS) appeared in China and rapidly spread to Viet Nam, Thailand, Europe and the Americas. It is due to a coronavirus (a family of animal viruses). It is now thought to be primarily a bat virus which is carried without bats showing signs of illness. It is contained in respiratory secretions and feces. They probably spread it at wild animal markets in China to civet cats and then to man. It was then able to fully cross the species barrier and spread from man to man. Poor hygiene and close contacts allowed it to rapidly become a problem. There is no vaccine and no real effective treatment other than life support in an ICU. SARS now seems to be contained but is still lurking in such places where bats, civet cats and other wild animals are bred and sold. Avoidance of such places is your best and only protection.