Hijacked cells turn into virus factory

By MARTIN JOHNSTON health factory

If influenza viruses had hands, they would rub them with glee every time they saw a flu sufferer sneeze.

Each flu-infected nasal explosion showers millions of freshly made viruses into the mouths and noses of friends, family and bystanders - "hosts" who are mostly unaware of the microscopic battle that may be about to begin inside them.

Flu viruses, and their cousins in the common-cold family, get into humans mainly by infected droplets that have been sneezed or coughed out - a reaction caused by the inflammation of the airways. But we can also pick them up on our hands from infected objects and then pass them to our mouths and noses.

Many people confuse flus and colds, until they get bowled over by the flu.

It can be a far more serious infection, especially for the young, the elderly or those with weakened immunity, and is a potential killer.

People will suffer far more colds in their lifetime than bouts of flu.

Flu symptoms mostly include a high fever, headache, severe cough, muscular pain, weakness, and sometimes sneezing, a sore throat and stuffy nose.

Sneezing and coughing are usual, and a cold, and sore throat and stuffy nose are common. But other characteristic flu symptoms are much milder and a fever is rare.

Cold viruses invade the mucous lining of the nose and throat. Flu viruses do that and also infect the lower airways and lungs.

Both have proteins on their surface which recognise proteins on the outside of human cells. Infectious diseases physician Dr David Holland says these proteins allow the viruses to "dock" on to the cell.

"They hijack the cell's normal molecular Machinery and make millions of copies of themselves."

In less than 12 hours, in a process that is the same for any virus, the host cell dies and the new viruses leave to infect more cells.

With flu, the sweating, fever and shaking body are results of the body's immune system fighting back. It does this in various ways, such as producing interferon and antibodies.

Interferon is a chemical which shuts down human cells' ability to synthesise proteins, making them resistant to the viruses' attempts to dock on to them and replicate inside.

Once immune system B cells have recognised the virus, they produce tailor-made antibodies that latch on to the virus, neutralising the proteins the virus needs to dock.

T cells help recognise the virus and specialised "killer" T cells kill viruses and infected cells.

Neutrophils and macrophages "mop up" dead cells and viruses, and they contribute, along with fluid from inflammation, to the mucus that can clog up the airways of flu sufferers.