[bdevine]

It's not clear from the article that that's a smoking gun. Just prior to that point, we see:

"Elevated levels of radon and carbon monoxide were detected but later ruled out as a cause.", with a link to a Russian page that, Google Translated, seems to actually indicate that CO is still a leading suspect. However, the article immediately goes on to apparently quote from the same Russian page that

"...some of houses (sic) of the affected residents had carbon monoxide levels that were ten times higher than recommended. This... could have caused similar symptoms to the “sleeping sickness”."

So the article itself seems a little sloppy. Beyond that, I wonder what the sickness relationship is between high-CO houses and all inhabitants of them, given that at least one inhabitant per house has experienced the sickness. Is there a correlation? Also, is the social structure of the village such that there are frequent visitations to most or every home? If so, then one might expect to experience the sickness even if one's own house doesn't have high CO.