An apparently innocuous bout of the flu may leave lasting footprints on the functioning of the brain, causing severe memory impairment, warns a new research.

Dr Ole Isacson of Harvard Medical School notes in a paper published in Science Translational Medicine that infectious diseases such as influenza can affect brain cells to such an extent that they might be damaged beyond repair, eventually leading to Alzheimer's.

The risk of cell damage remains at its peak a few weeks after the initial infection, the paper suggests.

Degeneration of brain cells is usually caused by an inflammatory immune response to the flu virus, Dr Isacson predicts, adding that viral infections can be a precursor to "some of the most common neurological diseases".

Although the chances of developing Alzheimer's with just a single bout of the flu are slim, the Harvard professor warns that influenza, together with factors such as long-term stress and injury to the brain, can render the cranial cells dead and initiate the beginning of the end for the brain.

It is important to control the inflammation to cut the risk of flu-induced Alzheimer's, the expert suggests. Referring to an earlier survey of 135,000 people suffering from the flu, Dr Isacson points out that the participants who took medication quickly to treat inflammation had 30% lesser risk of developing Parkinson's – another degenerative disease involving brain cells – compared to those who did not take any medication.