Bird flu, chickens, Turkey and pandemics.
For the first time the deadly strain of avian influenza virus, H5N1, has killed outside South East Asia. The first a 15 year old boy from the rural east of Turkey, then four days later his 15 year old sister and then tragically their 11 year old sister. A whole family devastated by one of the worlds most feared diseases. “Turkey in shock” was one national headline. As this article was written another 15 suspected cases have been reported across Turkey. What has triggered the spread of ‘bird flu’ out of Asia and into Eastern Europe?
The natural hosts of the H5N1 strain of influenza virus are birds, primarily wildfowl such as ducks and geese, which often harbour the virus but show no signs of infection. Unfortunately influenza can be transmitted to poultry and being more susceptible they succumb to infection and die of the disease. Infected birds also become reservoirs for the replicating virus, which is spread to other birds and occasionally to a human host via their faeces. The natural migration route of wild birds from Asia is the most likely explanation for the spread of bird flu into Eastern Europe.
The reason South East Asia has been the centre of human H5N1 infection is the population’s practice of living in very close proximity to their poultry and hence increasing the likelihood of infection. In areas of dense poultry production and where people live with their birds, the chances of acquiring bird flu are greatly enhanced.
There is no evidence to date that H5N1 bird flu is able to pass directly from one human to another. The only route of human transmission is from poultry to man. The H5N1 strain of influenza remains a bird-specific virus, although there is a real possibility that it may become endemic in poultry.
The practice of culling large numbers of chickens and turkeys, in areas where bird flu is present, is currently the best method of controlling the spread of the disease.
Will H5N1 cause the next influenza pandemic? Historically the answer should be no. The previous three influenza pandemics of 1918 (H1N1), 1957 (H2N2) and 1968 (H3N2) were genetically different from the current H5N1 strain. Some argue that the next pandemic will be caused by a previous pandemic strain, as the majority of the global populace will have no immunity to these viruses anymore. However, there remains the possibility that H5N1 will mutate sufficiently for human to human transmission, and only then will it have the potential to cause a pandemic.
To date H5N1 has caused 77 deaths world wide; compared to more than 30 million during H1N1 pandemic of 1918. This is no excuse for complacency though, as the rapid spread across Turkey suggests that the virus passes easily from chickens to humans. The danger is H5N1 mixing with a human influenza strain and acquiring the propensity for human transmission. The more people who are infected with avian H5N1 the greater the chance of genetic exchange with human influenza. Recent evidence now demonstrates, historically, that the 1918 pandemic strain was also originally an avian influenza virus.