If your in SoCal, we are fortunate enough to somehow breed the unkillable spidermite. They hibernate for no reason at all so it takes weeks of treatments and miltiple methods to kill. A certain percentage will not be killed by whatever you use, they really are the borg. You just need to keep a continous cycle of knocking them down...
It's not just SoCal, Lost, it's all of California. And not just resistant mites, either. Resistant fungus gnats and diseases as well. Like Septoria.
I'd rather deal with any of those than mosaic virus, though, simply because not only is there no treatment (just reducing spread), but if you try to make seeds it will be passed through those, just forget about clones.
Are there any threads on quarantine procedures here?
There is a proper QT protocol for public aquariums and it begins with observation in a quarantined area (no cross contamination by people, and for certain animals other additional measures are taken) and the specimen
must go 30 days disease-free before it's placed into display. This goes for everything, and I wouldn't be surprised if all zoos use such a method as well.
I think it should also be noted specifically about spider mites that they can be carried on clothing (as amstercal has alluded). The only infestation I have had to date was caused by bringing my son into my grow areas.