by Michael Woodhead
A H7N9 influenza pandemic may be confined to Chinese people because of a susceptibility gene that makes them much more prone to severe H7N9 disease, a new review has noted.
The IFITM3 gene (interferon-induced transmembrane protein-3 gene) increases influenza disease severity, but it is uncommon among Caucasians, a report in the journal Clinical Infectious Diseases notes.
The IFITM3 gene is more common in Chinese people and could account for a widespread population risk of severe H7N9 infection, says Dr David Hui of the Chinese University of Hong Kong.
In a commentary on risk factors for H7N9, Dr Hui notes that recent research has shown that 70% of Chinese patients who had severe influenza infection had the susceptibility gene. The gene is associated with a six-fold higher risk of severe influenza, he notes, and has also been linked to higher influenza mortality. A genetic susceptibility may also explain clusters of the infection in family members.
The study released last year concluded that: "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
Dr Hui also remarks on another surprising finding from a new review of influenza patients: smoking appears to be protective against hospitalisation for the disease. This 'counter-intuitive finding' might be due to some anti-inflammatory effect of nicotine, he suggests.
The review found that H7N9 influenza tended to affect older men and those with co-morbidities such as cardiovascular disease. It also had a more protracted course than other forms of influenza, with an average time from onset to death of 18 days.
UPDATE: Another recent study has shown that compared to Caucasians, Chinese people have lower levels of an immune protective mechanism against H7N9 influenza virus known as CD8+ T lymphocyte (CTL) immunity. The same study also shows that Alaskan and Australian Indigenous people may be particularly vulnerable to H7N9.