Swine flu variant disables lungs clearing mechanism: new study

A variant of last year's pandemic influenza linked to fatal cases carried a mutation that enabled it to infect a different subset of cells lining the airway, according to new research.

The study, due to be published in the Journal of Virology, suggests that the mutant virus could have impaired the lungs' ability to clear out germs. The researchers behind the study, from Imperial College London, the Medical Research Council National Institute for Medical Research and the University of Marburg said the findings highlight the potential for deadlier strains of flu to emerge and spread.

The 2009 pandemic of H1N1 influenza caused thousands of deaths worldwide, but the majority of cases were relatively mild. A variant of the virus carried a mutation termed D222G in a protein on the surface of the virus, and people infected with this variant were more likely to have severe and fatal illness.

According to a World Health Organisation report, the D222G mutation was found in less than two in every hundred cases of 2009 pandemic flu, but was responsible for around seven in every hundred deaths.

Viruses infect cells by attaching to receptor molecules on the cell surface. Different receptors are present on different cell types, and a virus can only infect cells that have the right receptors for the protein on its own surface.

The new research shows that flu virus with the D222G mutation can bind to a broader range of receptors in the airway, including receptors that are present on cells called ciliated cells. These cells, found in the lining of the airway, have hair-like projections called cilia.