5 ms·
That’s certainly already the case. Ivermectin has lost effectiveness against particularly insidious parasites such as Haemonchus Contortus (barber pole worm).
by crazyjncsu 5y ago
That’s certainly already the case. Ivermectin has lost effectiveness against particularly insidious parasites such as Haemonchus Contortus (barber pole worm). We’ve resorted to other treatments such as Moxidectin, Levamisole, etc, all of which are more expensive and harder to dose safely and effectively.
I can totally understand how Ivermectin got its following— it’s an amazing general purpose medicine around the farm. I generally use it responsibly by verifying the presence of parasites before administering (which can be literally any animal on the farm with almost any parasite) … but then there are times such as when my daughter had a single pet chicken (among many healthy ones) that wasn’t looking so hot … Whereas previously I’d just dispatch the animal and be done with it, now I give a dose of Ivermectin and isolate for a few days before calling in the grim reaper. So far the success rate is something like 90% where now my 9 year old daughter administers it herself. While I acknowledge this isn’t the most responsible, I can imagine others have had similar experiences which explain some of the popularity of Ivermectin with rural folk.
- WithinReason 5y agoWhat's the downside of giving Ivermectin to livestock that don't have parasites?
- mumblemumble 5y agoIvermectin stops working.
- WithinReason 5y agoThrough what mechanism?
- mumblemumble 5y agoNatural selection.
- WithinReason 5y agoHow will natural selection act on parasites if there are no parasites in the animal?
- technothrasher 5y agoIt obviously cannot. But the issue isn't giving it to animals without any parasites, it is in giving it to animals with parasites but that do not need the anti-parasitic in order to recover. Once you have determined that the animal is sick enough to need treatment and that the sickness is most likely caused by the parasites, then you can make the decision that the risk of furthering resistance is outweighed by the need to treat the animal. If you have determined that there is no chance the animal has parasites, then there's no risk of furthering resistance but also no need to give the treatment.
- mattmcknight 5y agoI think this largely right, but resistance generally does not just evolve in the animals "that do not need it to recover", as all parasites/bacteria are more likely die in that case, but in more extensive cases where some of the parasites/bacteria survive and there are more reproductive events that can introduce a resistant genetic variation. This is why some consider that people not completing the full course of antibiotics- only taking them until they feel better, may be a greater contributor.
- mumblemumble 5y agoIn nature, both the antiparasitic and the parasite will have a tendency to end up in places that you don't necessarily want them to be for the purposes of motivated hypothetical reasoning.
- fragmede 5y agoaka the chicken will urinate out some amount of ivermectin, unprocessed by the chicken, and then some amount will make it elsewhere that will allow for natural selection to take place (eggs or wherever). Once is infinitesimal, but give every animal some ivermectin for funsies, and you've now bred ivermectin resistance.
- h2odragon 5y agoThere's an issue with collies and collie-derived dog breeds; used to be warnings (even mentioned in an episode of "House"). But. Most of the lines running around today are the ones that weren't sensitive and didn't die from ivermectin. So it's no longer such an issue.