There are mainly three types of influenza virus – A, B and C:

Type A:

This is the most virulent form and is not exclusively a human disease. Birds are particularly susceptible to a variety of type A flu viruses which can then mutate and cross the species barrier to humans. This is what has occurred with the H5N1 strain or “bird flu”. Type A flu causes the most severe illness. The resulting symptoms, caused by the body’s immune response, can be fatal and this type of flu has been responsible for various pandemics over the years, with Spanish flu (H1N1) in 1918 causing 40 million deaths.

Type B:

This type infects mainly humans, and is much slower to mutate. Due to its apparent inability to cross the species barrier, it has fewer possible hosts who ultimately become immune until the strain eventually manages to mutate. For these reasons Type B is less common and does not cause pandemic threats.

Type C:

The C variety infects humans and pigs but is less severe, particularly in children. This type of flu gives rise to symptoms similar to a heavy cold (this is where the line between a cold and flu is blurred) and is less serious.

Influenza is spread through the air by droplets containing the virus. Coughs and sneezes, produced by someone with the virus, will contain thousands of spores. Once airborne they are ready to be inhaled by anyone in the vicinity, thus spreading the virus. It can also be spread through physical contact and for this reason it is helpful to wash hands frequently and particularly before eating.

The most defining sign of flu in all cases is its rapid onset, with just a few hours between feeling well to feeling unbearably ill. It might start with a fever or chills and a vague dry cough or sore throat. Headache, aching limbs and sometimes nausea or vomiting quickly follow and very soon the patient is too ill to do anything but take to their bed. Symptoms usually peak for 24-48 hours after which the patient is left feeling weak and with similar symptoms to a cold such as a cough, runny nose and loss of appetite. It make take 1 or 2 weeks to fully recover during which time the patient is still infectious.

Complications can occur in the young, the elderly or the sick and these are mostly due to secondary infections such