Compared to other viruses in the H7 family, H7N9 has evolved to bind effectively to mammalian cells and even to reproduce at the lower temperatures found in Humans – as opposed to the relatively warmer-blooded bird population. In fact other viruses in the H7 group have been found in poultry stock in several countries including the UK and USA, but they have produced only mild disease in humans: conjunctivitis or minor respiratory symptoms. As H7N9 causes a severe pneumonia, producing death in 22% of cases, and has now been imported to other countries, some may ask if this virus is the next Ebola?
The answer is a clear no, however. Firstly, although it is a very serious disease for humans, transmission from human to human is particularly difficult, thus limiting its potential to start an epidemic. The vast majority of infections have occurred following direct exposure to affected poultry in farms or markets, and not from infected individuals. Thus when in affected regions, care should be taken if visiting such markets: frequent, effective hand washing should be practised, as should the washing and peeling of any foodstuff bought. In most cases these environments should be avoided, however.
Secondly, in distinction to Ebola, there is effective antiviral treatment that has been proven to reduce the effects and mortality of H7N9. Such medicine was given to both of the Canadian patients, who were not in fact admitted to hospital but only required self-quarantining at home. Whether these individuals had a milder response to the virus, or were treated so rapidly as to spare them from severe symptoms necessitating hospital attention, is unclear.
Dr Simon Worrell BSc MBBS MRCP, Head of Medical Communications, Healix International.