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Bird flu: Jargon & Confusion.

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  • Bird flu: Jargon & Confusion.

    Bird flu: Jargon & Confusion.

    I am a criminal and I am not alone. My crime is the sloppy use of language when talking about the ‘bird flu’ pandemic threat. I was reading a BBC ‘have your say’ thread in which the dangers of a pandemic were being mainly attributed to media hype and a typical comment would be ‘this disease has only infected 200 people in 10 years it is not a real threat’, I have also seen a number of questionnaires with questions like ‘how likely do you think you are to be infected with bird flu in the next year?’. In both cases the problem boils down to the use of the term ‘bird flu’ to mean quite different things.

    First let’s try and clear up some terminology. Influenza virus comes in three Types A, B & C (‘Type’ here is being used in its technical meaning not its common language meaning). Seasonal human flu can be type A or B and human flu pandemics - at least those for which we know the causative agent – have been Type A. For the rest of this piece I am going to ignore types B & C.

    Type A influenza is an ‘encapsulated single stranded ribonucleic acid virus’ (ssRNA). It has 8 strands of RNA which encode its genetic material which include instructions for the manufacture of 11 proteins. Two of these proteins Hemagglutinin (HA or H) & Neuraminidase (NA or N) are surface proteins and are therefore ‘visible’ to our immune system and are important in our immune response. Type A influenzas is subdivided into Serotypes based on these surface proteins, there are 16 different Hs and 9 Ns giving a total of 144 permutations of which H5N1 is one.

    So we have Types & Serotypes and within a serotype we have continuous genetic mutations leading to different Strains (also used in its technical sense). Similar Strains can be grouped together into Clades & Subclades.
    Some examples; the H5N1 virus circulating in Vietnam (Clade 1), Indonesia (2.1 i.e. clade 2, subclade 1) and Europe (2.2).

    The natural reservoir for all these Type A viruses are birds so originally they are all bird flus. Occasionally they mutate to a point where they are sufficiently well adapted to infect some other animal as well and if they can sustain infection within the new host they gradually adapt to become a flu of that species. A disease (not limited to flu) that infects humans from another species is called a Zoonotic. AI H5N1 (note the AI suffix which stands for Avian Influenza) is at this point, as it is not a native human disease, but is being caught primarily from birds. If efficient human to human (h2h) transmition is achieved a new disease will have emerged H5N1 (N.B. no AI suffix) and, as it is novel to the human immune system, it is likely to spread rapidly causing a pandemic.

    AI H5N1 is often referred to as HP AI H5N1 (also referred to in the media as Asian H5N1), the HP stands for Highly Pathogenic (technically this is defined by the structure of an area on the HA protein but for our purposes we will view it as a measure of virulence) as opposed to LP AI H5N1 (low path. or North American H5N1) which also exists but is not known to cause human infection and causes mild illness in poultry.

    H5N1 is not the only AI that needs watching, H7 strains have caused severe illness and death in humans and demonstrated h2h and could just as easily be the cause of a pandemic.

    Having – hopefully – clarified some of the terminology used in discussing ‘bird flu’ we can have a look at ways the use of ‘bird flu’ in particular and - to a lesser extent other terms with specific and general meaning e.g. Strain - have lead to confusion. Some scientists, and others, who fully understand the differences between all these terms use ‘bird flu’ as convenient shorthand relying on context to clarify what they meant, however if they are then quoted, without full context, then the meaning becomes ambiguous. Some media articles quote multiple extracts from different sources in the same piece without explaining that each source is using the term to mean something quite different. So BBC blogger comments like ‘this disease has only infected 200 people in 10 years it is not a real threat’ should be excused for not realising the difference in risk between AI H5N1 zoonotic infections, which rarely occur, and an H5N1 pandemic – the real threat – which could erupt at any time and cause million or hundreds of millions of deaths in short order. Likewise the ‘how likely do you think you are to be infected with bird flu in the next year?’ question has radically different answers depending on whether ‘bird flu’ means HP AI H5N1, Pandemic H5N1, any newly emergent (in humans) Type A Serotype etc.

    As always, feedback welcome. Is it clear? Is it accurate? Was it helpful? How can we improve it?