Dr. Michael Egnor is, once again, trying to explain why evolution isn’t important to medicine. This time he’s responding to Mark Chu-Carroll’s post on Tautology. In his latest post, Egnor continues to challenge the conventional wisdom that an understanding of evolution in general and natural selection in particular is essential to understanding and dealing with the phenomenon of bacterial resistance to antibiotics.
Here’s his latest statement along those lines:
Mark, your dad’s illness didn’t happen because his doctor didn’t know enough about random mutation and natural selection. Our battle against bacterial resistance to antibiotics depends on the study of the intricate molecular strategies bacteria use to fight antibiotics, and our development of new antibiotics is a process of designing drugs to counter the bacterial strategies. We use molecular biology, microbiology, and pharmacology. We understand that bacteria aren’t killed by antibiotics that they’re resistant to. We understand tautologies. Darwin isn’t a big help here.
Thus far, Dr. Egnor has only discussed the phenomenon of bacterial resistance in general. I’m going to present a pair of real, specific, and relatively recent scenarios where I think an understanding of evolution by natural selection has played an important role in public health debates involving appropriate uses of specific antibiotics. My question – and challenge – to Dr. Egnor is this: can you explain why an understanding of evolution by natural selection was really not important in these specific cases? If you cannot, can you please explain why you still believe that an understanding of evolution by natural selection is irrelevant to medicine?
The first case is one that I wrote about back in 2005. I just reposted the material over to this blog if you want to read about the case in detail. If you don’t, here’s the Cliff Notes version:
There were a couple of antibiotics (fluoroquinolones) that were being used to treat E. coli infections in poultry. Due to the logistical difficulties involved in treating individual birds under typical farming conditions, the antibiotics were administered by adding them to the water supply for the birds, and giving them to the entire flock. The FDA became concerned about the effect that this treatment method would have on another bacteria – Campylobacter. Campylobacter does not make birds sick, but it can make people sick. Specific mutations have been identified in Campylobacter that can make the bacteria resistant to fluoroquinolones, and other studies have shown that those mutations do not make the bacteria that have them less fit when fluoroquinolones are absent. The FDA believed (correctly) that adding those antibiotics to poultry water supplies acted as a selective pressure that favored antibiotic-resistant strains of Campylobacter, and, because the same class of antibiotic is used to treat Campylobacter infections in humans, ordered that the drugs be removed from the market.
I’m having a hard time seeing how that series of events could reasonably be described as anything other than an application of our understanding of evolution by natural selection to a potential public health problem. Dr Egnor, do you have an alternative explanation?
The second case is more recent, and has been discussed at length here at Scienceblogs. This one involves the pending approval by the FDA of a veterinary usage of cefquinome to treat respiratory disease in cattle. A number of groups, including the AMA and some of the folks at the FDA’s human medicine side, are arguing very strongly against this approval. Why? Because cefquinome is a 4th-generation antibiotic that is used to treat drug-resistant bacterial illnesses in humans. A good bit is known about how resistance to these antibiotics evolves, and the AMA (et al.) are very concerned that administering the drug to cattle will create more environments where the evolution of resistance to cefquinome is selectively favored.
Again, to me this looks like a very clear, and very simple, application of the principle of evolution via natural selection to public health. I was under the impression that public health is part of the medical field – but maybe I’m just being fooled by all the public health departments at med schools. Any thoughts, Dr. Egnor?