Periodically flu pandemics strike, causing severe illness and sometimes death. Bird flu and swine flu make international headlines when they go on the attack. Understanding just how these virus particles wreak havoc will help scientists to develop therapeutic interventions.
A flu virus is a simple beast, essentially some genetic material wrapped up in a protein coat, yet it can cause so much disaster. For example bird flu virus symptoms include fever, sore throat, and severe bouts of coughing. Swine flu virus symptoms are similar to seasonal flu virus symptoms and include fever, chills, and fatigue. Both viruses can be fatal. The 1918 flu virus killed between 20 million and 50 million people according to estimates.
There are two types of surfaces proteins;
Haemagglutinin - this is the H in H5N1 and it is a surface protein that is a target for the immune system. There are 16 known types of haemagglutinin protein in bird flu viruses, and three of these are found in human viruses. H5 means it’s the fifth type of the protein. Haemagglutinin causes red blood cells to clump together, which is how it got its name. It binds to a sugar known as sialic acid, which is located on the cell surface of virus host cells.
Neuraminidase - there are nine types of this cell surface protein in humans and birds. N1 stands for the first type of this protein. Neuraminidase helps new virus particles to bud off from cells.
And then there are ….
M1 Matrix Protein - once new viral RNA particles have formed the M1 matrix protein helps to package them together and transport them to the cell membrane.
M2 Ion Channel - when a host cell engulfs a virus particle its aim is to destroy it. One of its methods is to release acid, but the virus is able to use this to its advantage. The acid is pumped through the M2 ion channel which activates the release of viral genetic material.
Viral RNA - carries the instructions to make new viral particles.
One of the deadliest types of bird flu virus is the H5N1 strain. Scientists have worked out one of the reasons why it could be such a killer. Researchers from Vietnam found that the viral load (the concentration of virus in the blood) in people infected with the H5N1 strain is much higher than in those people with normal human flu.
The team observed that the high viral load caused the release of proteins called cytokines and they were at their highest levels in people who died. In these people there was also a loss of lymphocytes in the blood and scientists believe that both factors caused lung damage, and in some cases, death. Therefore the higher the viral load the greater the chances of death, and so medicines such as Tamiflu, which can reduce the amount of virus in the body will be of benefit.