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Avian Influenza: A serious threat to humans?
10/7/05 | Alan P. Zelicoff, MD
Posted on 10/09/2005 7:27:34 AM PDT by woofie
The headlines have been terribly frightening: in generally staid journals, including Nature, Science and even Foreign Affairs, entire issues have been devoted to fears of a coming pandemic of avian flu due to a new subtype of bird flu called H5N1, first identified in 1996 in SE Asia and now circulating widely among birds – both migratory and agricultural – in China, Russia, and most countries of east Asia. Are the fears of spread of this influenza to humans justified?
Experts – who are inevitably quoted in the popular media – have advanced four main reasons for concern: first, that “pandemic” flu (i.e. truly global in spread and high in incidence) comes in regular “waves” and that we are “overdue” for a new subtype of flu against which humans have no immunity. Second, since some humans (about 100 to date) have acquired H5N1 influenza, apparently directly from birds, it appears that this new subtype does not require the usual “mixing” with other strains of influenza in an intermediate mammal (usually pigs) in order to ‘adapt” to humans. Third, since a substantial percentage (perhaps half; no one knows for sure) of humans who have acquired H5N1 have died, that if the illness becomes transmissible from human to human there will be an extremely high mortality rate in the epidemic. And finally, since H5N1 is carried by migratory birds, it is only a matter of time that highly lethal influenza (for humans and also for other birds) is spread around the globe.
Each of these arguments is conjecture at best and scientifically specious at worst. There is no evidence that pandemic influenza comes at intervals. Indeed, since the few pandemics we have seen (1918, 1957, 1968 and perhaps a few in the 1800s that were very poorly documented) are caused by random reassortment of influenza genes (in humans or other mammals) the probability of pandemic occurring is the same every year (and it is a small number). Just like flipping a coin, random reassortment means random pandemics, not periodic ones. We are not “overdue”, just simply no more due this year than we have been in any year. Yet, we are spending billions of dollars on anti-flu medication stockpiles.
Next, we simply don’t know how many humans have been infected directly from birds since no serologic (antibody) prevalence studies have been done - the ONLY way to answer this question. Indeed, it may be the case that contact with H5N1 carrying birds confirms immunity to most humans. Considering the billions of close interactions between live chickens and humans in Asia, if H5N1 influenza does transmit from birds to humans, it does not do so easily. And, while there is NO doubt that H5N1 is highly lethal in chickens, basic evolutionary biology would predict this to be the case because chickens are densely packed in chicken houses or egg-production operations. Thus, the virus does not depend on a relatively healthy, mobile host to spread, rather it can kill its host because other victims are always nearby. This is probably why the 1918 influenza pandemic was the worst in history: humans were packed nose to nose in trenches, hospitals and hospital ships in WWI, and cities were crowded with tenements and heavily used public transport. Such conditions do not exist today.
Finally, since dead birds don’t fly, it is IMPOSSIBLE for migratory birds to spread a lethal virus (lethal to them, at least) over large distances. Whether or not the less-lethal virus they do carry will be lethal to chickens or humans remains to be seen. We can take some reassurance that vaccines of the past decade include the “N1” component of H5N1 and will doubtless offer some protection.
In the end, the only way to settle the debate – and to prepare for the very small chance of a pandemic – is via continuous, real-time clinician driven surveillance of animals and humans. This real-time surveillance enables front line public health providers to exchange information and identify the severity and likely source of a novel epidemic immediately such that they can effectively battle the problem before it spreads beyond control.
An excellent mission statement for a thread entitled, "Avian Flu Surveillance Project." Thanks for posting.
Finally, since dead birds don’t fly, it is IMPOSSIBLE for migratory birds to spread a lethal virus (lethal to them, at least) over large distances. Whether or not the less-lethal virus they do carry will be lethal to chickens or humans remains to be seen. We can take some reassurance that vaccines of the past decade include the “N1” component of H5N1 and will doubtless offer some protection.
First while sick birds can not fly those that have been infected and survive can still shed the virus. Also many birds coexist with the virus in their gut and thus are not killed off. They are the natural reservoir for Flu. Among these are waterfowl. Also from my understand it is the H not the N that cause immunity.
Indeed, since the few pandemics we have seen (1918, 1957, 1968 and perhaps a few in the 1800s that were very poorly documented) are caused by random reassortment of influenza genes (in humans or other mammals) the probability of pandemic occurring is the same every year (and it is a small number). Just like flipping a coin, random reassortment means random pandemics, not periodic ones.
The interval of pandemic is not a scientific certainty true; however, the recent scientific study of the 1918 flu shows that no re assortment is necessary. And thus the Bird flu of 2005 resembles that of 1918 very closely. This is not the same as flipping a coin in that regard. We have a pandemic of FLU every year. Tens of thousands die. The difference between the yearly pandemics and the 1918,1957 and 1968 pandemic is that a Flu virus mutated significantly enough so that our bodies could not readily identify the virus. Thus more people died of the Flu in those years. With 1918 being totally different and killing upwards of 50 million. The difference wit turns out was a complete jump from bird to human. Much like what is occurring in 2005.
And, while there is NO doubt that H5N1 is highly lethal in chickens, basic evolutionary biology would predict this to be the case because chickens are densely packed in chicken houses or egg-production operations. Thus, the virus does not depend on a relatively healthy, mobile host to spread, rather it can kill its host because other victims are always nearby. This is probably why the 1918 influenza pandemic was the worst in history: humans were packed nose to nose in trenches, hospitals and hospital ships in WWI, and cities were crowded with tenements and heavily used public transport. Such conditions do not exist today.
The conditions not only exist today but are far worse in many parts of the world. China, India, Indonesia, major African cities, Mexico, Brazil, New York, London and on and on. All of these Cities and Countries have huge populations packed together in close quarters. In 1918 the rural population was 80% and 20% in cities today that is switched. As New Orleans showed there is mass poverty and overcrowding not only in 3rd world countries but the inner cities of the USA also. The world population has grown exponentially since 1918. We now have close to 8 billion. In 1918 the population of the US was around 100 million today it is close to 300million. We still have wars going on in Afghanistan, Iraq and our military are in more places around the globe then in 1918. We cram people into unventilated aircraft for 4,6,8,12,hour flights. Finally our economy is totally different today then in 1918. We were able to provide for ourselves to some degree in 1918. Today the majority of people get their food, clothes, entertainment, etc from stores. I remember Dickens it was the best of times it was the worst of times.