There is no absolute proof yet (among other things, because one obviously cannot experiment on humans) but everything suggests that resistant Leishmania not only survive better in humans have a higher "fitness" but also are better at making people ill have a higher "virulence" than their non-resistant counterparts.
It is the first time that science finds an organism that always benefits from its resistance. Normally resistance is only useful when a pathogen is bombarded by drugs; the rest of the time it is detrimental to the organism.
Resistant organisms are a real problem to medicine. More and more pathogens become resistant to our drugs and antibiotics to a large extend because you and I use them too lavishly and improperly. For several microbes, the arsenal of available drugs and antibiotics has so diminished that people may die again from pneumonia, or even from ulcerating wounds.
Luckily for us, resistance helps pathogens only in a drug-filled environment. In the open field their resistance is a disadvantage to them, because they have to invest energy and resources into a property with no use there. Just like a suit of armour is quite useful on the battle field, but a real nuisance the rest of the time.
So the propagation of resistant organisms is substantially slowed down because they are at a disadvantage outside of sick rooms. But this rule, too, is violated by Leishmania: even in absence of the drug, the resistant parasite survives better, instead of worse, and it is more virulent than a non-resistant parasite.
Did our medicines create a superbug? A legitimate question, and the phenomenon has to be investigated, but this sole case doesn't imply we better stop developing new medicines (as a matter of fact, the antimony-resistant Leishmania are still suscep
|Contact: Jean-Claude Dujardin|
Institute of Tropical Medicine Antwerp