I can tell you're getting a little bit tired of repeating yourself on this. :) I also have no doubt that most of the "it's not working" cases are exactly what you describe, and that it must be extremely trying to deal with such unfounded claims on a daily basis. However ... :-)
Well, it's not so much that I'm tired of it, I just don't know what else I can add beyond what I've said. However...:-)
To summarize on my earlier comment here http://avetsguidetolife.
- I have used the product successfully for some time, which pretty much rules out "user error".
- My conclusion that there is something wrong is not based on expectations concerning the environment, but simply on the observation of large (!) amounts of flea feces and most notably eggs on the dog, in contrast to the excellent performance of the treatment at another location. By my understanding of the products workings, a treated dog should not carry significant amounts of eggs.
It's highly unusual that you are seeing eggs on your dog, and that may not be what you are actually seeing. Flea eggs are not easily visible to the naked eye, being smaller than the feces ("flea dirt" or "fleaces"). They are smooth, shiny, and white in color. The eggs are also designed to fall off the animal as quickly as possible, which is how the fleas are spread in an environment. Once a flea lands on a suitable host it stays on that host for it's life and doesn't jump from animal to animal. The fleas move around by the eggs falling off the animal where ever it goes. So if you are seeing actual eggs, this is very unusual and something I don't even see on highly infested pets. Here are what flea eggs look like, magnified many times.
- Frontline DOES work here, but only for a much shorter interval then the initial 30 days, which, when being able to rule out other factors, which I of course am not qualified to do, it *is* an indication of increased resistance.
- I have observed the problem over three treatments, all of which have happened after 14-20 days of the previous treatment, with the problem becoming painfully obvious after only two weeks, which means the product must have stopped working a bit before that.
- I do not claim this to be a general problem, but can only report this for a specific area of a specific city.
Actually, all of this can be explained without resistance. In fact, this exact scenario is what Dr. Dryden looked at in Florida and what other researchers have investigated. When you have an area (city, yard, neighborhood) with an excessive and overwhelming population of fleas, the sheer numbers can overcome the products. Because it takes some time for the fleas to die, when you have high numbers they can keep jumping on (and yes, keep feeding) before they actually die. Again, this type of situation has been looked at by independent scientists and in every case (so far) found not to be resistance.
Also, once a flea egg is laid it can take 3-6 months to become an adult. That's why you have continued fleas emerging for months on end even with appropriate medication usage since some of the fleas you're seeing today may have actually been eggs laid last year. Then you have wild animals and stray pets moving through an area regularly and you are getting constantly re-infested with new flea eggs. What this means is that in areas with high stray and wild animal populations environmental control is nearly impossible.
- Resistances are more likely to develop, if a population is repeatedly exposed to small doses of a chemical. Untreated street dogs here are abundant, in addition to treated household dogs often spending most of their day on the street near their home. (Few people actually have a backyard here and literally no one walks their dog. They just let them out during the day and back in at night.)
Treated and untreated dogs constantly having close contact means the flea population on the untreated dogs is often exposed to very small concentrations of Frontline. It's pretty much the perfect example of accidental natural immunization. :)
- Frontline is the primary flea treatment used here. (I had to check three drug stores to get Advantix, and they just had one pack under a huge stack of Frontline.)
Now I do agree with the general principle here, and this makes logical sense. In fact, the scenario you describe is normally how resistance develops in any species and to any product. So you are thinking along the right lines and have a good understanding of the scientific principles involved. However, even that being said there hasn't been documented resistance (I'll get back to that in a minute).
- The company producing the treatment is not a reliable source of information, because when isolated incidents of actual resistance become obvious, the information policy is all that decides the end of the products lifecycle. Meaning: even if they know about it, publishing it would be very expensive. It is far more likely that it would cause them to invest into the research for an efficient upgrade to the product and, when it's ready, market it to replace the current one without losing the general investment into the product line. (Yeah, I know evil corporate conspiracy theory, but I've worked for one long enough to know how they think. :)
I'll agree with you again here. I've seeing data from every company about how their product has studies to show that they're faster, better, and work longer than any competing product. Obviously they can't all be right, so there must be some bias involved in the study design or interpretation. This bias is why I rely more heavily on university researchers and independent studies by people who aren't on a pharmaceutical company's payroll.
- I agree that no reliable evidence against the products effectiveness exists, but as you said, resistances can happen, and I'd even go one step further: They are likely to happen sooner or later. If rare cases in isolated locations start to happen, it will take a while for them to spread and become generally know. I also know that to cross the borders with a dog here, flea treatment is mandatory, and the Andes to the east and the desert to the north make for pretty efficient natural borders.
Here's the point that I wanted to get back to and why I'm careful to state "documented" or "proven" resistance. I agree that eventually resistance will likely happen. In fact, I'm surprised that Advantage/Advantix hasn't seen any resistance over the years as much as it's been used. Just because resistance hasn't happened doesn't mean that it won't. A few years ago nobody was considering resistance of heartworms to common preventions. Yet we now have documented populations of resistant heartworms in certain areas along the Mississippi River in the US, and it's becoming more of a concern as we worry about these parasites spreading beyond their current borders. The situation you describe in Chile is certainly conducive to resistance, and we may see it develop there and in other areas.
Taking all this into account, I do conclude that my personal observations and the lack of another explanation are at least an indication towards an increased product resistance here. Advantix, which I am using now, working as expected would support this, since it is using a completely different active substance. I'll report back. :)
P.S.: If by not being convinced you mean that you will not accept observations from just some guy on the internet as evidence, then I can't really dispute this. Arguing with common sense is futile. :)
As I said before, I don't completely discount the fact that resistance may be happening in your area. But the situations that you describe (many fleas despite appropriate use) are also seen in parts of the US, have been investigated, and have been proven to not be due to resistance. So there are other explanations that make complete sense to the parasitologists.
Great discussion, Thomas! I enjoy these kinds of intellectual debates where everyone is bringing up logical points and can be polite and rational.