DEFRA announced an outbreak of Avian Flu north-east of Preston on Friday and have just confirmed the strain is a highly-pathogenic H7N7. We saw an outbreak in February this year of a low-path H7N7 avian influenza in Hampshire but this new outbreak is far more serious – for birds. The risk of it causing human disease is incredibly low.
In this context ‘highly pathogenic’ means it is highly contagious in flocks and will result in a high mortality rate in birds – but it is not the H5N1 avian strain which has led to hundreds of deaths in people worldwide and is also distinct from the H5N2 strain of avian flu that caused the recent outbreaks in the USA.
Most types of bird flu are harmless to humans but two types – H5N1 and H7N9 – continue to cause serious concerns. Other bird flu strains – including H7N7 – can and have infected people, but cases are very rare or have only rarely caused severe illness.
A temporary control zone imposed on Friday at the affected farm has now been replaced by a 10km surveillance zone with an inner 3km protection zone. Culling of all 200,000 birds at the farm is continuing. The restrictions mean that all poultry farms within the 10km control zone around the infected premises are not allowed to move poultry, captive birds or other animals except under licence.
Human infections with avian flu are rare, and the virus found in Lancashire is not seen as a major concern for human disease – the receptors in humans that avian flu strains can bind to are deep down in the lungs so to get it you need to be working with large numbers of infected birds and breathe deeply. It is not passed from person to person.
But while this particular outbreak has few public health implications, flu remains a serious illness that is a prolific killer both directly and indirectly, particularly in the very old, the very young, the pregnant, the obese and the infirm. You can find out more by clicking below and if you have any questions about the current outbreak or flu generally please contact us.
[spoiler title=”Flu Facts” style=”prime-color” icon=”fa-question-circle”]With every new flu strain to hit the headlines we seee headlines saying it will be a repeat the 1918 / 19 pandemic – the one that killed as many people as both World Wars combined in a single season. Could this one? Unlikely. Will it? No one knows – despite the apocalypse some journalists always predict. Aside from pandemics don’t underestimate seasonal flu either (and that means proper flu caused by the influenza virus, not the sniffles or ‘man flu’) – seasonal flu kills 500,000 people per season directly and a lot more indirectly.
Flu strains are judged by their virulence in humans (the ability to cause disease or death) and how infective the are (the ability to spread). Deaths by influenza mainly depend on the virulence of a circulating strain and pandemics such as the 1919 H1N1 were both virulent and infective. Some strains, such as H5N1 (bird flu) or H3N2 are more likely to kill (60% for H5N1) than strains like H1N1 – which was of only moderate virulence but highly infective. So H1N1 is easy to catch but isn’t as nasty as some, H5N1 is a shocker but you need to work quite hard to get infected.
The H7N7 in the news doesn’t spread person-to-person but it’s really good at infecting birds and if it mutates (and flu always does) it might become both virulent and infective. But that’s not a certainty; mutations always carry a cost and as a rule if a strain becomes more infective the likely quid pro quo is that it will become less virulent.
The biology of flu virus is relentlessly fascinating. There are horse, pig, bird and human varieties and they generally stick to their host species. One reason we don’t usually get avian strains is that the cells in our body that avian strains can bind to are few and low down in the lungs, but receptors for human stains like H1N1 are in the upper airway which is why H1N1 is far more infective in humans. So to get an avian strain you need to be around a lot of poultry and breathe deeply.
But pigs have both receptors in abundance. So they can get a human, avian and swine flu all at once. And the flu virus keeps its 11 genes in 8 segments, not in a single sequence of RNA. So if a pig is infected with more than one strain it can mix together elements of them all. This ability to shuffle the pack (combining elements from different strains) is called genetic shift. This is how new strains emerge. And if the new strain is both virulent and infective we are in trouble. This is also the reason most new strains tend to arise in places where people, pigs and chickens live in close proximity. This is why new strains tend to come from place like Asia where you often find families, pigs and chickens in close proximity.
Just to be difficult flu also undergoes genetic drift over time; in addition to its ability to change dramatically due to genetic shift it’s not very good at copying itself accurately – so it mutates lots. This means a particular flu strain knocking about at the start of a season will be slightly different at the end of it. These changes are the principal reason the flu vaccine needs to change from season to season and the experts need to gamble on which strains will be circulating in a year’s time.
You can find out more about the flu virus, its epidemiology and the vaccine at our Science Blog. [/spoiler]
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