Saturday, 20 April 2013

Against A Prospective Ban On Sale Of Live Poultry

On Wednesday earlier in the week, I picked up a copy of the China Post whilst waiting for a take-out (there were no copies of the Taipei Times), and I was surprised to find a letter published therein from Thomas L. Knapp, on the subject of Bitcoin, prompted no doubt by its' recent crash. I'm quite sure that this would never have seen the light of day in the Taipei Times due to the biases of the TT editorial office. However, the China Post house editorial piece on the same page was of a completely different nature...

This is in response to the news of outbreaks of a different strain of Avian Flu virus in China, and the fear that it could find its way across the Taiwan Strait to infect and kill people in Taiwan much like the SARS did over a decade ago. Preventing the spread of infectious diseases might be regarded as legitimate grounds for State intervention, even by people otherwise sympathetic to libertarian concerns. The reason for this is that the probability of collective action succeeding in containing the spread of the virus may be more easily and more drastically reduced by a relatively small number of people who refuse to cooperate. In comport with that idea, the editorial calls for the ban on the sale of chickens and ducks in traditional markets around the country since the handling and butchering of these birds takes place outside the safety regulating purview of the State.

However, this argument relies on at least two unstated assumptions - neither of which is likely to be true in my opinion. 

The first assumption is that the virus is particularly deadly, which is to say that it will kill a large proportion of the people it happens to infect. I think this is unlikely to be true for several reasons; first, viruses that are deadly tend to be rare and viruses that are not deadly tend to be very common and this fact implies differential reproductive success, or in evolutionary terms, there is selection pressure on virus strains to avoid killing their hosts; second, the deadliness of a virus throughout a human population is likely to be exacerbated by things like malnutrition and poor hygiene - both of which are conditions that are increasinly absent in a developed country like Taiwan; third, exposure of a population to a greater range of virus strains, as is consequent to greater travel and trade, probably means increased immunological resistance to any "deadly" virus strains that are nontheless genetically similar to the many, many more non-deadly strains.

The second assumption is that the spread of the virus can be successfully contained by stricter control over the treatment and slaughter of poultry (and that this can be performed successfully by the government). Leaving aside the fact that most poultry in Taiwan is raised domestically (in fact, I would suspect that most poultry imported from China is sold in supermarkets rather than traditional markets) and therefore restricting imports of poultry ought to be sufficient for a containment strategy, there is a further point to be made, which is that the basis of the scare is that the virus is said to be able to infect humans from birds! It would stand to reason therefore that a successful containment strategy ought to target not just the containment of the virus from the movement and slaughter of birds, but also the movement of people. If the strategy is to be taken seriously, then all travel of people to and from China would have to be banned too, yet the editorial does not call for that.

Besides that, the editorial reads too much like a call by friends of the big supermarkets to use the latest Avian Flu virus scare to eliminate their market competition. How large are domestic sales of poultry in traditional markets compared to sales of poultry in supermarkets? I don't know, but they would have to be marginal for the suspicion to be erased and given that there are hundreds of traditional markets all slaughtering chickens and ducks up and down the country nearly every day, I doubt that it is marginal.

I might turn this into a letter and write to them just to see if they'll publish.


  1. Actually, I think the danger is that the virus has the potential to kill a lot of people. "large proportion" has to be taken in context with number of people infected. The danger any virus poses lies not just in its deadliness, but also in its infectiousness. Even a 1% fatality rate is pretty bad if hundreds of millions are infected.

    As for the comments on reproductive success, I would say that's more of a long term thing which doesn't really apply for a newly mutated strain which is perfectly fine with doing the whole mutate into a monster, rampage around, and then burn itself out routine. As a reproductive strategy it's bad in the long-term but great in the short-term if you keep spreading fast enough.

  2. Yes but infectiousness will surely be limited by (a) a broader distribution of immune resistance than in the bad old days (e.g. 1918), and (b) good hygiene and even just half-decent nutrition and healthcare. So I doubt we'll ever see a pandemic of Ebola or anything like that.

    "I would say that's more of a long term thing which doesn't really apply for a newly mutated strain which is perfectly fine with doing the whole mutate into a monster, rampage around, and then burn itself out routine."

    Yes, that's true but the point is about probabilities, not that it can't happen. A deadly monster is far less likely than another garden variety of mild flu and this is partly due to selection pressures, but also, as mentioned above, a broader distribution of immunological resistance across populations. By all means vaccines and other mechanisms for infectious disease control should be prepared, but it should not be taken too far or else it'll be a bit like insuring your house against lightning strikes.

  3. From the looks of it, H7N9 is deadly; currently the mortality rate is around 20%. But it can't spread person-to-person (or if it can it's been contained) so things are good. The chances of it mutating into something that can are low but they increase when humans and birds have too much contact. That's why this ban has been discussed since 2006, it's not just about H7N9, it's about preventing disease-from-birds in general from ever becoming a serious problem.

  4. Blob - I would have replied to this earlier, but I've been too busy...

    The 20% mortality rate is derived from only 102 cases, of which I would suspect the 20 fatal cases were most likely elderly people with weak immune systems. If that's true, then it might be more illustrative of what is really happening to say that H7N9 only has a high mortality rate among the old and weak and a very low, or even zero mortality rate among the young and strong. This is similar to regular human-strains of influenza which also typically kill off the old and weak rather than the young and strong.

    We might be better off focusing on improving our own nutrition, exercise and health in general to boost our immune systems naturally rather than panic-culling chickens and putting people out of work with stupid laws.


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