Or, "Everything you ever wanted to know about bird 'flu but were too afraid to ask."
On the weekend we found out that a Bernard Matthews' turkey rearing unit in Suffolk has suffered the first outbreak of H5N1 bird 'flu in farmed poultry in the UK, I think some hysteria-free information is in order.
So, what's this bird 'flu, anyway?
So called "bird 'flu" is more correctly Avian Influenza. The Influenza virus is an Orthomyxovirus. Avian influenza is an Influenza Type A virus. Influenza A viruses can infect many other species, including humans, pigs, horses, mink, seals, and whales. The bird 'flu we're currently concerned about is known as H5N1.
H5N... what sorry?
Influenza viruses are classified according to the precise form of two of the proteins found on the virus surface. HA binds to the surface of target cells allowing virus entry, NA binds to and hydrolyses a component of the infected cell membrane to allow the progeny virus to escape at the end of the infection cycle. There are 15 variations of HA and 8 of NA. Particular viruses are named for their HA and NA proteins, hence H5N1 in this case. Almost all combinations of HA and NA exist in wild birds, and in most cases the viruses are genetically stable (do not mutate) and apathogenic (do not cause disease).
Apathogenic? What's going on here, then?
Infection of new host species pushes a process known as antigenic drift - a succession of mutations affecting key proteins which affect the virulence (disease causing potential) of the virus. Low Pathogenicity Avian Influenza (LPAI) outbreaks can see the mutation of the strain into a Highly Pathogenic Avian Influenza. HPAI, and LPAI can be transmitted between birds, with LPAI more easily transmitted because infected birds remain alive and secreting the pathogen for long periods. HPAI causes the rapid death of up to 100% of an infected group of animals, as we have seen recently in the Bernard Matthews' outbreak.
So, hang on, we're talking about an animal health issue here?
Yes, primarily. The reason for the media panic about Deadly Bird 'Flu is a second habit of the Influenza viruses called Antigenic Shift. Antigenic Shift can occur when two different influenza viruses infect the same host at the same time. The genetic code of the two viruses gets jumbled up and new versions of the virus appear containing some of the genetic material from each virus.
What's that got to do with this Bird 'Flu, then?
We've all heard about the cases (mostly in the Far East) of people dying of this H5N1 bird 'flu. As the BBC News website put it today, these cases have essentially been restricted to those in 'intimate contact' with infected poultry (yeah, thanks for that image, Auntie Beeb!). There have also been a few cases where people infected in this manner have gone on to infect family members, and these cases are described as 'horizontal transmission'. It is clear, however, that H5N1 'flu as it stands isn't easily transmitted to people or between them. The concern about epidemic 'flu is that the H5N1 strain we're seeing at the moment could either, via Antigenic Drift become more infectious to and between humans, or (probably more likely) meld with a human virus and produce a highly lethal, highly contagious human 'flu via Antigenic Shift. A good whack of the current paranoia seems to stem from the perception that we're somehow 'overdue' an epidemic 'flu. There's a whole 'nother can of statistical worms there that I'm not going to get into right now!
OK, so what has all of this got to do with me?
At the moment, the most likely answer is 'nothing', if you don't keep or work with poultry. If you work commercially with poultry, you should be receiving official government advice. As part of the vigilance programme the government would like you to keep your eyes open for dead birds while you're out and about. If you find dead wild waterfowl (gulls, waders, ducks, geese or swans) DEFRA would like you to 'phone 08459 33 55 77 and let them know.
Can't I get vaccinated with this Tamiflu thingy?
*Sigh*. The media have really got their knickers in a twist about this one. Tamiflu is not a vaccine, it's an antiviral drug which it is believed might reduce mortality in cases of infection with influenza. Relenza is another, similar drug. The NHS is stockpiling both of these, and Tamiflu has been offered to people who were working with the infected flock or involved in the slaughter operation. There's also the standard, seasonal 'flu vaccine. There is no evidence, or rational scientific reason, to believe that this would protect you in any way from either this H5N1 strain or any of the infinite possibilities for what it might have transformed into should it become highly infectious to humans. There are experimental H5N1 vaccines in production, but no guarantee that they would still have any effectiveness after whatever mutation event created an epidemic 'flu.
But, hang on, I've got half a dozen chickens in my garden!
If you have registered your flock with DEFRA (and, I can see why people with small flocks may have chosen not to undergo voluntary registration, given what a paperwork-and-faff machine DEFRA generally is!) you should be receiving advice in due course. If you are in the Restricted Zone or Surveilance Zone for the present outbreak, then restrictions apply to how you can keep your poultry and on poultry movements. For more information see the DEFRA website below.
Outside the Zones for the current outbreak, common sense applies. The most likely source of infection to farmed birds is the faeces of wild birds. Keep your birds seperate as far as possible from wild birds. Especially do what you can to prevent wild birds having access to the feed and water your poultry use. Keep feed and water bowls clean and replace food and water regularly. Feed and water indoors or under cover if possible. If your poultry are kept in a fenced enclosure, a tarpaulin over the top may reduce the risk of wild birds contaminating the enclosure with their droppings. Above all, be vigilant for signs of disease in your animals. Apart from sudden death, symptoms of Infuenza in birds may include depression and inappetence, dramatic reduction in egg production and facial oedema (swelling) with swelling and cyanosis (blue-coloration) of combs and wattles.
Further information
http://www.defra.gov.uk/animalh/diseases/notifiable/disease/ai/index.htm - DEFRA's Bird Flu advice website. Contains information for poultry keepers and members of the general public. Includes detailed advice to poultry keepers and maps of the Surveilance and Protection Zones.
http://www.defra.gov.uk/news/latest/2007/animal-0203.htm - DEFRA's official press release on the Suffolk H5N1 outbreak.
http://www.hpa.org.uk/infections/topics_az/influenza/avian/default.htm - The Health Protection Agency's Bird 'Flu website.
http://news.bbc.co.uk/1/hi/health/3422839.stm - And if you want to be confused, read the BBC's "Q*A - Bird Flu".
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