Flu viruses

There are three types of influenzaA viral infection affecting the respiratory system. virusA microbe that is only able to multiply within living cells. - types A, B and C. They differ in the internal proteins that they contain.[1]

Influenza A virusesMicrobes that are only able to multiply within living cells. can infect different animals (an infected animal is called the hostAn animal or plant that supports a parasite.), including birds, humans, horses and pigs. Influenza B virusesMicrobes that are only able to multiply within living cells. infect only people. The main hosts of influenzaA viral infection affecting the respiratory system. C are also human beings, although C virusesMicrobes that are only able to multiply within living cells. have been found in pigs too.[1]

Influenza A virusesMicrobes that are only able to multiply within living cells. cause the most serious illness in humans. These virusesMicrobes that are only able to multiply within living cells. have the ability to escape detection by the antibodiesSpecial proteins in the blood that are produced in response to a specific antigen and play a key role in immunity and allergy. of the human immune systemThe organs specialised to fight infection. - this is called antigenic variabilityA change in the antigens on the surface of a microbe, which may result in it escaping detection by the immune system.. Influenza type B also has antigenic variabilityA change in the antigens on the surface of a microbe, which may result in it escaping detection by the immune system., although to a lesser extent than influenzaA viral infection affecting the respiratory system. A virusesMicrobes that are only able to multiply within living cells.. Influenza type C causes a less severe illness than either A or B, and is more similar to the common cold.[1]

When a person is infected, the fluA viral infection affecting the respiratory system. virusesMicrobes that are only able to multiply within living cells. they carry can be spread by coughing or sneezing, so that the virusA microbe that is only able to multiply within living cells. is released into the air and may reach another person.[1] Person-to-person spread may also take place via contaminated surfaces such as door handles or taps, and from shaking hands.[2]

References: 
  1. Hampson AW and Mackenzie JS. The influenzaA viral infection affecting the respiratory system. virusesMicrobes that are only able to multiply within living cells.. MJA. 2006;185(10 Suppl):S39-43.
  2. Zambon MC. Epidemiology and pathogenesis of influenzaA viral infection affecting the respiratory system.. Journal of Antimicrobial Chemotherapy. 1999;44:3-9.