To understand human infection of the virus one needs to understand viruses. The influenza or flu viruses have spikes projecting from their surfaces. The are two different types of spikes. One is made of a protein called hemmagglutinin (HA). There 16 different subtypes of HA proteins. This protein allows the virus to stick to the cell it is getting ready to infect. The second protein is called neuraminidase (NA). There are nine different subtypes of NA proteins This protein allows the new virus to exit the host or infected cell.
Flu viruses are classified into three group A, B or C.
This classification depends on the different proteins they contain. Type A viruses are found in many different types of animals; ducks, pigs, chicken and in humans too. Type B viruses are found mainly in humans and type C are found in pigs, dogs and humans too but do not cause epidemics. Type A is the most aggressive of all the flu viruses. Its is said to have been responsible for some the major global flu outbreaks. Type A viruses are further subdivided into groups based on the two surface proteins HA and NA. For example the Hong Kong virus is called (H9N1) as it contained type 9 of the hemmagglutin and subtype 1 of neuramindase protein. The human flu virus currently circulating among the human population are H1N1, H1N2 and H3N2. Viruses are tiny bundles of genetic material that are enclosed in a shell called a viral coat or capsid. Viruses exist for one purpose only and that is to reproduce or make more viruses. They achieve this goal by putting their genetic material into the host cell. Once in the infected host cell the viral genetic material inserts its self into the host’s genetic material. The host is then instructed by the viral genetic material to replicate many times. This allows the virus to make a numerous copies of its self. The host cell is also instructed by the viral genetic material to assemble new virus which grow numerous in numbers causing the host cell to burst or release the new viruses. They are also picky as to who they infect. A virus can only infect and cause havoc in one species, and may not have a noticeable effect in another.
Transmission Route of Bird Flu Virus to Humans
The flu virus has existed in wild aquatic birds such as ducks. The virus does not necessarily affect the birds. The virus often mutates (changes it genetic material) and “jumps” across the species barrier to infect domestic poultry and then to pigs and other domestic animals. The pig acts as the “mixing bowl” as the pig can be infected by both human and avian viruses simultaneously. The viruses come in close to each other and exchange genetic material allowing the new virus to spread from pigs to people. This was thought the route that avian or bird flu spread to humans but about ten years ago it was discovered that bird flu skipped the pig step and infected humans directly. This triggered the fear of a pandemic ( global scale non-seasonal epidemic). Fortunately for now, the virus can not spread effectively from human to human. This however is a matter of time, as the flu virus is constantly changing. This why the health officials are constantly developing new vaccines yearly to combat that particular years prevalent strain.
Bird Flu in the Human Body
Once infected by the bird flu viruses infects the cells in the human lungs. Normally the virus attacks the cells that are deep in the lungs where the exchange of oxygen and carbon dioxide takes place. The symptoms of a bird flu infection are similar to the regular human flu infection namely fever, cough, muscle fatigue and sore throat. These symptoms may further develop into pneumonia and acute respiratory illness and other life-threatening illnesses.