What quackery? A quick google confirms that chickenpox has been speculated to have caused a serious epidemic among Native Americans. We know that European diseases wiped them out, it just isn’t necessarily clear which ones due to the lack of record keeping and medical knowledge at the time.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2957993/

> In the years before English settlers established the Plymouth colony (1616–1619), most Native Americans living on the southeastern coast of present-day Massachusetts died from a mysterious disease. Classic explanations have included yellow fever, smallpox, and plague. Chickenpox and trichinosis are among more recent proposals. We suggest an additional candidate: leptospirosis complicated by Weil syndrome.