The identification of a single case of bird flu virus H5N8 on a duck farm in East Yorkshire led to the immediate enforcement of a 10km containment zone last week. Within just 24 hours, officials began the cull of 6000 ducks on the farm operated by Cherry Valley, the UK’s largest producer of duck products.
This immediate and robust action leads to questions regarding the severity of an outburst of this globally experienced disease. More than 20 teams of environmental officers were at the farm in Nafferton, near Driffield last Tuesday afternoon. Considering it’s only an hour’s drive away from our university, should we be worried?
Background to bird flu
Bird flu – also known as avian influenza – is an infectious disease of birds, of which there are currently 15 different strains, some of which can be deadly. Wild birds worldwide often catch the virus but do not get ill from the infection; 84% of the susceptible population are chickens and farm birds. The virus can be highly contagious, spreading through contact with infected excretions, secretions, feed, water or surfaces.
For poultry, some forms of the disease are rapid killers, with mortality rates of 90-100% owing to the shut down of organs occurring within just 48 hours of infection. In other cases, if the disease is of low pathogenicity the birds may show no symptoms, but remain as carriers.
Bird flu is a zoonosis disease. This means birds are its main target, falling foul to its capability to disturb the vascular system causing brain, heart and lung haemorrhages along with often a non-recoverable breakdown of the nervous system. However, mutations can result in a crossing of the species barrier with strains which put humans at risk.
Strains that have been found to infect humans include the H5N1 virus, and more recently the H7N9, which can be fatal for birds and humans alike. Human transmission occurs through close and continuous contact with infected birds, or through eating infected undercooked poultry.
Previous outbreaks
There is a geological pattern associated with incidences of bird flu.
The disease occurs more frequently in Asia, which is partly due to the cultural and economic situation; with huge chicken populations in unhygienic conditions kept in close quarters, the infectious disease is able to fester.
As for global transmission, the disease spreads through the migratory habits of birds, but also through legal and illegal poultry trades, as patterns of incidence have followed transport links, railways and cross-country borders.
In China, the new N7N9 strain of the virus emerged in March 2013 and became contagiously transmittable to humans. According to the World Health Organisation (WHO), the initial three people infected in China turned into a counting toll reaching 453 of human cases, 173 of which were fatal. As of yet no cases of N7N9 outside China have been reported.
This month in Europe
Despite the rarity of its occurrence in Britain, it seems the disease has been cropping up increasingly across Europe this November. Along with the recent identification of H5N8 bird flu in Yorkshire, there have been outbreaks of the same strain earlier this month in the Netherlands and Germany. The World Organisation of Animal Health (OIE) tests have revealed that the strain found in these European countries was the same strain that swept through Korea earlier this year.
What’s there to worry about?
The strain at the duck farm in East Yorkshire, H5N8, is not easily transferable to humans and, as confirmed by the British environmental secretary, is of low risk to public health.
However, what is worrying particularly for farmers is the source from which this bout of bird flu stemmed. It is thought that the disease arose from exposure to infected droppings, brought about by birds migrating across Europe. It is impossible to control this process of natural wildlife behaviour, which means the exclusion zone implemented at Nafferton farm has no real impact upon the primary source of the disease. This not only puts the other 2.5 million vulnerable farmed birds in East Yorkshire at risk, but also all other birds across Britain.
The avian flu virus has a high mutation rate; genetic material can be relatively easily interchanged due to the structure of the genome. This results in the birth of new strains or sub-strains, which are accompanied by the creation of new threats to humans and wildlife. Whilst the strain at Nafferton isn’t easily transferable to humans, mutation is a potential worry. This was the case with the H5N1 strain, which evolved with a capability to infect humans, sweeping from Asia to Europe and then Africa, taking the lives of hundreds of humans and millions of poultry on its flight.
The Chinese case of H5N1 caused a panic, with the British government ordering 14.6 million courses of the drug Tamiflu, is a Swiss developed vaccine drug targeting symptoms of bird flu with the intention of decreasing its spread.
So as for the bird flu causing a ruffle an hour’s drive away from you, there is no need to take flight from Leeds just yet, although under the circumstances, it’s probably best to double-check that your Christmas turkey is fully cooked.
Harriet West
Feature Image: jakealford.com