February 10 Flu Update
Helen Branswell here with an article that has the potential to be the most important development in avian flu in many months. If it bears out, it could mean even more than that. She reports that scientists studying the prevalence of flu deaths in young people wonder if there is not widespread existing immunity in people over 35. Entire article is a must read.Nearly 90 per cent of the people who’ve been diagnosed so far with H5N1 avian flu were under age 40, a new analysis from the World Health Organization shows.
And two British scientists suggest that as yet unexplained phenomenon could be a clue that widespread immunity to infection with this virus may exist in people aged 35 and older.
In a letter to the March issue of the journal Emerging Infectious Diseases, Matthew Smallman-Raynor of the University of Nottingham and Andrew Cliff of the University of Cambridge note that the age distribution of H5N1 human cases is "consistent with a biological model of geographically widespread immunity to avian influenza A (H5N1) in persons born before 1969.
West Java woman dies of bird flu in Indonesia. She is from a village where four other people are sick.
Scandal ensues in Britain concerning the Bernard Matthews turkey company and its imports of Hungarian fowl, which continued after Hungarian birds were the suspected cause of the Suffolk outbreak.
More on the hospitalized cases in Turkey, reported yesterday. This report says there are 3, not 4.
The source of the infection for the deaths in Nigeria has not been determined yet. The birds there appear to be domestically raised.
Meanwhile, efforts are underway on the ground to stem the tide of the bird flu.
A third avian outbreak is reported in Pakistan.
South Korea found its sixth outbreak of bird flu among birds, and the culling begins.
A dead magpie in Hong Kong is H5N1 positive.
Dr. Nabarro says outbreaks are less than last year, but more widespread...
he also says H2H is a possibility.
The NHS is Scotland is preparing for bird flu.
More Branswell, here on wild bird surveillance.
A man who had cycled in SE Asia came home to Cyprus with flu symptoms, but has now tested negative. Note that this didn't come until after panic had ensued.
A media guide for journalists is now available on line.
A graduate of Illinois Wesleyan who works at the Mayo Clinic returned to his alma mater to warn of bird flu risks.
posted by Orange @ 10:51 AM
3 Comments:
Orange;
Well, you probably could have predicted that I would zero in on the Helen Branswell article and put my two cents worth in. What a chick she is, I’m impressed.
My take on the news that the WHO data indicates a hidden widespread immunity to the H5N1 influenza virus that may exist in populations aged 35 and older , is once again, precautionary. Some people will view this empirical data through clouded prisms and misconstrue or let down their guard, especially if they are older. Much more research needs to occur before any conclusions are reached. For right now, it is a very sharp double-edged sword.
The role that diseases and immunity play in an epidemic is interesting, fascinating and often frightening, and definitely has to be viewed in the right context. Epidemiologically, when pandemics first appear, they are spectacularly fatal to a large portion of the world’s population, like 1918, and they are so lethal that they appear to die out completely. But, after a certain period of time, both host and viruses re-adjust to each other, and as in the case of ordinary influenza viruses, they then become a normal endemic “stable” part of society. What happens is that this less destructive relationship becomes more secure for the influenza viruses, and they must count on a fresh supply of susceptible new hosts (children or young people), to infect in order to perpetuate their existence. What actually happens is that indeed the older people have acquired an immunity to certain types of influenza, which has been reinforced by repeated exposures through their life.
There is an irony which also exists though. The more endemic and diseased certain people exposed to influenza viruses are, say for example in China, Indonesia and Nigeria, the less destructive its normal influenza epidemics will eventually be, as adults are less likely to die. The irony continues, because the more inter-contact action by transportation people have between Asia, Europe and North America involving normal Type A or B influenza everyday viruses, the less likely the chance of a supremely devastating influenza situation. However, here’s the real clinker in the theory - pandemics occur when an influenza virus, like H5N1, acquires new hemagglutinin and/or neuraminidase and becomes highly transmissible. After a pandemic or major epidemic, most people will be immune to the virus strain that caused it, similar to what occurred in 1918, 1957 and 1968. Any potential pandemic virus, like H5N1, will only have two options: wait until a new crop of young children are available, or recombine/mutate so that it no longer recognizable by the anti-bodies circulating in the previous victims or their direct ancestors. Studies of different age groups of mortality of various epidemics, have shown a relationship of those that survived exist because of suspected immunity acquired by resistance to prior influenza infections. So, Helen’s news is both good and bad.
Here’s another way to look at the dilemma: only when the radical mutation of a newly relatively unknown influenza virus, like H5N1, occurs and becomes highly transmissible, and there is little existing immunity in children or young people’s genes – we have the situation of devastating pandemic with the entire world serving as one gigantic disease pool. Older people may be less susceptible, younger people more so. Just like 1918 all over again, is what her data tells me. While most people view epidemics and pandemics as unpredictable, accidents or incomprehensible – they aren’t to me, they are all part of the natural infectious disease progressions that have gone on since people starting keeping written history records. Nature’s past influenza successes play a critical role in our current genetic toolbox, and it comes down to the particular influenza virus and type, the environment, and the multiple hosts involved.
So, no we shouldn’t be surprised that influenza mortality data possibly suggests an immunity or resistance in older people – this can be called the “herd immunity”. Vaccination against any influenza virus, should be viewed in a temporary “firebreak” sense in the spread of the disease. It is only when a very high percentage of any population is vaccinated, that influenza can be effectively stopped, and that situation is only temporary. Believe it or not, some European populations of the world have suspected natural immunities and resistance to TB and HIV, traced back 700 years to the selective advantage of the bubonic plague – but African populations do not, because they were never originally infected with it.
If a bird flu virus created the pandemic of 1918 and affected so many young people, think what we could expect today from this current rapidly spreading and mutating H5N1 virus with a > 50% mortality rate.
Wulfgang
Excellent comment as always. I guess my question is this: if true, would this make H5N1 not a pandemic-worthy virus? Or, at least, would it indicate the need for yet another mutation....
Orange;
I suspect you know the answers to these two questions before you asked them, but nevertheless, here goes.
The H5N1 virus is indeed pandemic-worthy and we should be extremely vigilant; and yes, without a doubt, based on history, more mutations and surprises are in order. The only frame of references we have, are to understand the epidemiology and immunology of past influenza pathogens of prior pandemics and the epidemics documented on record – that basically covers the last 100 years. I am going to attempt to do this in a couple of quick paragraphs.
The Helen Branswell (WHO) data indicates strongly that the current H5 Type A virus confers some immunity properties to persons born before 1969, based indirectly on three other common Type A viruses, that were once pandemic in nature, themselves – the H1, H2, and H3, specifically. However, it is not possible at the present time to predict how closely related the current H5 subtypes are exactly to these other Type A’s. To complicate things, if the WHO data is correct, further research needs to made about what kinds of influenza immunity this older age group has – it could be genetic (innate), acquired or adaptive, artificially acquired via numerous vaccinations, passively naturally acquired through their ancestors anti-bodies, or even passively artificially acquired as a result of anti-body injections. Since it is impossible to jump into a time machine and perform the serologic surveys necessary over the last 100 years, we can only speculate at this point. My guess is that this older age group exhibits some form of active immunity, resulting from prior clinical infections or repeated vaccinations.
The best information we do have, is what we know and don’t know about the 1918 pandemic, since all pandemics since then have been caused by its descendents, which are drifted H1 and reassorted H2 and H3 viruses, and draw a string of parallels on a few things. Since those aged 5-14 years old were disproportionately affected in 1918, it is believed that the virus was highly virulent (for some unknown reason), but, there was also a number of older people who acquired limited immuno-protection due to prior circulation of viruses at that time. There is no current definitive way I know of to predict whether the H5 virus has a parallel process of acquiring high transmissibility between humans. This is due to the fact that it is believed that even the three different waves of the 1918 pandemic may have been actually different strains or variants, since their three pathogenicities were vastly different. What is alarming everyone, of course, is that the 1918 virus was an avian-like influenza virus novel to that time, exactly like H5N1 is novel to our immune systems now.
The big unknown in my mind is the effect that poultry vaccines are having on the present H5 viruses, which makes it nearly impossible to predict. Asian countries, in particular China (those rascals), have been mucking around for nearly ten years introducing and reintroducing suspect (i.e. substandard) or insufficient quantities vaccines into their poultry, which has infected and re-infected wild birds, and other hosts, namely swine. I suspect this may be the root cause of the entire H5N1 threat, as these conditions have caused further cocirulation of the avian influenza viruses, that are in turn becoming increasingly pathogenic and virulent in nature. And you know the current situation of a pandemic virus for humans – there is none that perfectly matches the rapidly mutating H5 strains, nor can any come close to addressing the range of ones that are reassorting in swine, cats, or other mammals.
So, a long way around the barn, but I believe I may have answered your two questions – no to the first, and yes to the second. My total "speculation pandemic meter" at this point indicates to keep all eyes on Asia,Indonesia or China. That is where the Wulf predicts ground zero will abruptly emmerge.
Wulfgang
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