MDR & XDR TB - A Case of Bacterial Evolution

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Mefiante (October 11, 2006, 11:45:03 AM):
Yesterday's episode of e-tv's 3rd Degree discussed the case of 60+ deaths in KZN resulting from infection by extremely drug resistant tuberculosis (XDR-TB). Apart from being yet another very black mark against SA's health ministry (for its much-delayed reaction to timely and ample warnings), it is also an object lesson in just how critical a proper understanding of evolutionary processes can be.

But first, a little background information and a few comments: Tuberculosis is a contagious but curable disease of the lungs that worldwide currently kills about 1.7 million people a year. It spreads through the air, much like the common cold. The infective agent of TB is the Tubercole, or TB, Bacillus, which is a type of mycobacterium rather than a virus, as is the case with the common cold. At present, South-East Asia has the highest number of TB cases - about 33% of the world total - with an annual new infection rate of 182 per 100,000. However, sub-Saharan Africa's annual new infection rate is almost twice as high at 356 per 100,000.

Treatment in the form of antibiotics was first developed about 50 years ago, and TB incidence, prevalence and mortality rates declined sharply, to the point where it was felt that TB was about to become a thing of the past, much like smallpox. Treatments were therefore not developed any further. However, the normal treatment regimen is lengthy, taking six to eight months to complete, and is often accompanied by unpleasant side effects. The discipline required to see the treatment to completion is often lacking, especially in poor countries and rural areas where TB is most common. The discipline problem is aggravated by the fact that improvements are noted soon after treatment begins, and patients wrongly assume that their full recovery requires no further medication. Some TB bacilli survive the curtailed treatment, and the patient is almost guaranteed to suffer a relapse in the near future.

The salient facts of the treatment, such as its length, the possibility of unpleasant side effects and the necessity for completing it, are carefully explained to patients at its commencement, so it is a little spurious of 3rd Degree to attempt to blame the Dept. of Health alone. At least some of the responsibility must be apportioned to the patients themselves. Also, 3rd Degree did not spell out the full facts about TB treatment, which are central to the whole issue. The emergence of mmultiple drug resistant TB (MDR-TB) and XDR-TB was barely given the attention it deserved: one medical doctor was permitted to say that they resulted from "sub-optimal treatment."

Though truthful, that description is hardly complete, and explains nothing useful. The emergence of MDR-TB and XDR-TB is a direct consequence of incomplete treatment and evolutionary processes, and is exactly what evolutionary theory predicts will happen. In any population of TB bacilli, the available genetic variety will ensure that some bacilli are more resistant, and some less so, to the presence of a given antibiotic. The less susceptible ones will tend to survive, and pass on their antibiotic resistance to their offspring. Again, some of the new generation will be more, and some less, resistant, but on average, each new generation of bacilli will have a greater resistance than the previous one, provided that the antibiotic is present.

The antibiotic thus exerts a selection pressure on the bacilli, driving the entire bacillus population towards greater resistance. The few random genetic mutations that increase resistance in this regard - most will be neutral, and some negative - will be better adapted to their antibiotic environment and therefore survive preferentially, while the neutral and negative variations will quickly succumb to the antibiotic and die.

The way to cure TB then is to keep the TB bacillus population small by taking the appropriate medication for a lengthy period and allowing the body's immune system to mop up the surviving bacilli. If treatment is stopped too early, the immune system will not be able to cope and the more resistant TB strain will flourish. As has frequently occurred, repeating this cycle of relapse and incomplete treatment will amount to a selective breeding exercise where the relevant TB strain is effectively bred to be resistant to different types and potencies of antibiotics.

It is doubtful that new antibiotics can be developed quickly enough that effectively treat MDR-TB and, especially, XDR-TB. So we're basically left once again with the problem of implementing prevention and containment protocols, which, as has ever been the case, are considerably more problematic to administer than effective treatment management.

If nothing else, the above facts do, however, graphically illustrate the dangers and costs of ignoring good science.

'Luthon64
qrios (October 11, 2006, 12:43:00 PM):
Interesting post 'Luthon.... and I could not agree more on your comment..
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black mark against SA's health ministry (for its much-delayed reaction to timely and ample warnings), it is also an object lesson in just how critical a proper understanding of evolutionary processes can be.

Even her new medical tariff proposals for next year is ludicrous.

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Antibiotic resistance, like insecticide resistance, is not evolution as proved by the fact that both are reversible and soon disappear when the challenging molecules are no longer present. Like ontogeny is now, evolution WAS never reversible.

“At most, the environment plays a similar role with regard to organisms; IT CAN ONLY PROVOKE AND SET IN MOTION SOME POTENTIAL THAT IS ALREADY PRESENT.”
Otto Schindewolf, Basic Questions in Paleontolog, page 313, his emphasis.

Hence the Prescribed Evolutionary Hypothesis.

http://www.uncommondescent.com/archives/1675#more-1675

I was also reading on the development of antibiotics, and the ability to "evolve" into resistant strains, but unfortunately I gave not had the time to finish it all and conclude... :-[
Mefiante (October 11, 2006, 13:07:18 PM):
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Antibiotic resistance, like insecticide resistance, is not evolution as proved by the fact that both are reversible and soon disappear when the challenging molecules are no longer present. Like ontogeny is now, evolution WAS never reversible.
Hogswill and bilgewater. This response is typical creationist subterfuge: it deliberately misrepresents what evolution is. The fact is that antibiotic resistance is indeed reversible over generations in a given population. However, individual bacilli with enhanced resistance have to die off and be replaced by less resistant progeny so that the average population resistance decreases. You can't magically somehow make a given individual bacillus less resistant. The fact of reversibility is, in point of fact, entirely in line with evolutionary theory because removing the antibiotic again changes the selection pressures on the population and thus the environment it is in, so that increased resistance no longer matters, and therefore less resistant mutations survive and dilute the overall population resistance over time.

'Luthon64
Mefiante (October 11, 2006, 13:37:26 PM):
I wanted to add this to my previous post, but the edit period had expired.

There are certain species of fish that live entirely in dark caves. Their eye structures are gradually receding. By the creationist argument cited earlier, that shouldn't happen at all. Nevertheless, it does, and for the same essential reasons I gave before. In fact, eyes are detrimental in a perpetually dark setting because they are easily injured by bumping into things. Thus, such creatures with normal eyes are actually more vulnerable, and selection pressure is in favour of those specimens that have less easily injured (e.g. a thicker cornea or nictitating membrane) or smaller eyes. There's no selection pressure to maintain the eyes' ability to see because sight itself doesn't matter in the dark.

'Luthon64
qrios (October 11, 2006, 14:43:29 PM):
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Hogswill and bilgewater.
THE RECIPE FOR EVOLUTION!!!!! ;D - Sorry couldn't resist - Still can't believe that you find it plausible that the universe created itself ???

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You can't magically somehow make a given individual bacillus less resistant.
Do you imply that the opposite is somehow exceptable?

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The fact of reversibility is, in point of fact, entirely in line with evolutionary theory because removing the antibiotic again changes the selection pressures on the population and thus the environment it is in, so that increased resistance no longer matters, and therefore less resistant mutations survive and dilute the overall population resistance over time.

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Biological evolution ... is change in the properties of populations of organisms that transcend the lifetime of a single individual. The ontogeny of an individual is not considered evolution; individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest protoorganism to snails, bees, giraffes, and dandelions."

-- Douglas J. Futuyma in Evolutionary Biology, Sinauer Associates 1986

My argument is not against micro-evolution. I do believe it is possible as a creationary process. I am mainly anti-Darwinism...

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