To be fair, 'not licensed for use on poultry' doesn't necessarily mean that it is actually harmful to poultry, just that not enough research has been done into the effects of the substance on the target group, and especially its secondary effects such as transmission into meat or eggs, though of course I totally agree that it's good to err on the side of caution. Commercial chicken farming usually relies on an 'all in, all out' management policy, whereby a batch of pullets is moved into a shed which has been cleaned and disinfected after the previous 'crop' has been slaughtered at quite an early age. Having been inoculated as chicks against common diseases, any birds that subsequently succumb are simply culled and not treated - a different situation to domestic poultry keepers, who often prefer to try to treat individual pet birds when they can. If you're just treating a pet bird with a nasty infestation, probably that would be OK so long as you didn't want to eat the eggs, - just the same as for Ivermectin. But of course that's not so for commercial outfits, so money for research studies that would establish to what extent fipronil is actually safe on egg laying birds, or on meat birds, is not undertaken because it's not cost effective. Until now, it has been presumed that commercial chicken farms would simply not use it, as it's quite expensive compared with other forms of parasite control. I find it puzzling that apparently, so many in the industry have been doing so, since as has been said, it would be extremely difficult to apply as spot-on to hundreds of birds at a time.
Fipronil is licensed for use on dogs because it is effective against some common parasites (though not ticks) and can now be bought across the counter rather than only on prescription from a vet. As nobody in this country eats dogs, it is claimed to be safe provided that the owner is very careful when applying it, so it doesn't come into contact with human skin. The implication is that it can penetrate human skin just like canine skin, or be ingested from fingers which haven't been washed and which come into contact with the mouth.
The other spot-on treatments which are used on dogs and cats that do deal with ticks are only available on prescription from a vet, so are presumably even more potentially dangerous to human health. The most recent development in this field is called Bravecto, which is given in pill form to dogs and claims to provide complete protection, including from the more dangerous kinds of ticks, for up to 6 months. However, there is much controversy over its use, since it does not only affect skin but has to travel throughout the dog's digestive and organ system and affects the nervous system as well, in one large dose, from within. Hundreds of people worldwide have reported severe and even fatal reactions in previously healthy dogs, and there's a long-running Facebook site entitled Does Bravecto Kill Dogs? with all the details. I have had a long-running argument with my daughter over this, as her vet recommends Bravecto and her dog appears to tolerate it, but I am more cautious with my little terrier, having read all the research!
https://www.facebook.com/groups/411371212394679/
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