The Israelis have shown that jihadists like to toss together concoctions including everything they can find, so one cannot rule out that its a whole bunch of various toxic agents - perhaps arsenic (bloody vomiting), strychnine (for convulsions), and a whole lot of various junk. Or there could be a 'Love Canal' in the neighborhood. What I've seen of Russia, Ukraine, and Kazakhstan could qualify as a toxic waste dump ;-)
I've got no expertise to even hazard a guess, but I'm not buying the mass hysteria explanation. The symptoms are simply too severe. I trust you'll keep us informed.
The jihadis would be dusting not in Chechnya, but rather in the areas outside of it. And as for the Love Canal situations, again - why there? - there are too many crapped up sites outside of the conflict area, and more heavily crapped up, too. Thus one would expect it to be happening there first.