It has been almost ten years since the first case of avian influenza was reported in humans. However, in recent months the media has been abuzz with predictions of a major bird flu outbreak, caused by the H5N1 flu strain. So why is it that it seems like a more real threat now than before? According to the WHO, in the past two years 130 cases of H5N1 in humans have been reported, with mortality exceeding 50 per cent. Sounds scary, no? But is it as bad as it seems?
The avian influenza strain H5N1 currently only spreads among birds, and although it is highly infectious and deadly to them, its spread to humans has been rare and sporadic. Even though thousands of people must have been directly exposed to poultry infected with the H5N1 virus, relatively few have become infected. All of the affected individuals were in close contact with birds, so they were likely exposed to large amounts of virus and were particularly susceptible to it.
Sustainable human-to-human spread of this virus has not been reported. In order for the virus to be able to spread in this way, it would have to undergo specific genetic mutations. Since the virus mutates at a relatively high rate, there is a possibility that this might happen. However, the actual chances of it happening are small.
Furthermore, although H5N1 has a high mortality rate in humans in its current form, any increase in transmissibility in humans will likely be associated with a massive drop in virulence, because swiftly killing its host is a poor evolutionary strategy for a virus.
Even if the virus mutates and is able to infect humans, that doesn’t mean it will cause a deadly pandemic. The deadliest influenza outbreak in recent history, the Spanish flu of 1918, had a two per cent death rate. Based on previous epidemics, a group from Emory University has predicted that in the absence of intervention, the next flu outbreak would have about 0.6 per cent death rate if it were to become widespread in humans.
Although most experts acknowledge that another flu pandemic is inevitable, some wonder whether the H5N1 virus now circulating in Asia is really the one to watch.
One of the skeptics, Dr. Paul Offit, of the University of Pennsylvania School of Medicine, points out that H5N1 is not likely to be the next big pandemic since no H5 flu subtype has ever caused one in humans. Other researchers counter that if it does, it will be particularly dangerous, because the humans have no resistance to it.
Whatever the case, widespread prevention and detection methods are still an integral part of preventing an outbreak of H5N1. But there is no need to run in fear at the sight of a bird. At the moment, the avian flu does not pose a threat to the general public, and, speculation aside, nobody really knows when the next flu pandemic will occur and how deadly it will be.
Mariana Vidric is completing her PhD in U of T’s department of immunology.
