Because of a susceptibility gene, emerging and getting rampant H7N9 flu virus may only infect residents of China.

A report published in the journal Clinical Infectious Diseases by Dr David Hui of the Chinese University of Hong Kong said H7N9 flu virus spreads easily and more among the Chinese because of the IFITM3 gene (interferon-induced transmembrane protein-3 gene).

The IFITM3 gene is the one that increases influenza disease severity. It is more predominant among the Chinese people. Caucasians hardly have them, Mr Hui said.

This seemed to confirm an earlier study that said one factor the Chinese are susceptible to the H7N9 flu virus was because they have lower levels of an immune protective mechanism known as CD8+ T lymphocyte (CTL) immunity.

Dr Hui said that 70 per cent of Chinese patients who had experienced severe influenza infection had the IFITM3 susceptibility gene, which could explain the emergence or presence of infection clusters among family members.

"Because the risk genotype occurs with such a high frequency [in Chinese people], its effect translates to a large population-attributable risk of 54.3% for severe infection in the Chinese population studied compared with 5.4% in Northern Europeans," Dr Hui said.

On Tuesday, China reported two new deaths due to the H7N9 flu virus. The death tally has now reached a total of 25 since January, while the number of human infections has reached 113 cases. Zhejiang and Guangdong were the areas most affected.

The new H7N9 virus emerged only last spring.

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