There are many forms of influenza and not all are life threatening, the most cases can be treated, so there is no need for panic, the more aware of the situation you are the less likely you are to contract the infection.
This graph shows the levels of outbreak of a certain disease. Over the centuries humans have been under constant battle from viruses. These viruses are generated from animals that fall sick and go un-noticed or they could just be simple carriers of the infection. We all know that rabbits and hedgehogs and other wildlife creatures carry diseases but yet we live in harmony with these animals. We don’t bother them and they don’t bother us.
Level 1 is always in circulation in animals of the world. Wild animals will contract an infection and carry it to a different location or spread it to a different animal. In the wild this is a common occurrence between species but some animals are prone to infection and some are immune to the certain infection, if or when the infection is spread to a host that will catch this disease the infection will mutate within the host. When this mutation takes place in a certain animal the level is raised to level 2 on the scale.
The host could be aware of its illness and it may kill the animal or it may not, this all depends of the animals resistance of the infection, every animal is different even in the same species. It all comes down to the genetic make up of the animal. Bird Flu was the recent outbreak before the Swine Flu and as dangerous as that was it only reached level 3 on the pandemic scale. There has been multiple out breaks in the last 100 years and they seem to sweep the globe, mutating and causing humans harm. Foot & Mouth from sheep brought every country into deep concern, transport and general life was interrupter with disinfectant mats and vehicles being sprayed as they traveled from county to county and from country to country.
Level 3-5 are the worst stages of an outbreak, these are the stages where the infection has a host and is mutating and getting ready to infect a new host, such as humans. Again as level 1 and 2 there can be carriers and emmunancy in different animals. Their could be an animal such as a bird that catches this infection but does not become infected itself, these are carriers of the disease. Birds can fly making the infection impossible to stop from spreading, especially if it goes un-noticed. Not all infections can jump from host to host, between the levels 3-5 you would have to be in contact with the host, such as the swine flu it traveled from pig to human and then human to human. Aeroplane travel spread the disease from Mexico around the world. When the people got home to their countries they spread it by shaking hands with friends or hugging or kissing.