Reasons for suspected connection at least at key nutrient level:
- Active ingredient in both appears to be polyphenols
- Both sources appear to be micro-organisms that appear in and around mushrooms or the soil that they are in
Kitasato Institute isolated organisms from soil samples and carried out preliminary in vitro evaluation of their bioactivity.
- Heavy research was instigated into both avermectin (ivermectin precursor) AND how chaga mushroom extract works in the mid-to-late 1960s
- Ivermectin appears to be indirectly derived from quinine which was created from "the bark of trees"; Chaga mushroom grows on the "bark of trees in northern latitudes" (avermectin+HCQ=Ivermectin theory)
Some info to get you started if you want to dig into Phytonutrients:
20APR 2022; "Clinical Evidence of the Benefits of Phytonutrients in Human Healthcare": https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9102588/
15DEC 2007; "New antioxidant polyphenols from the medicinal mushroom Inonotus obliquus (Chaga)": https://pubmed.ncbi.nlm.nih.gov/17980585/
10FEB 2011; "Ivermectin, ‘Wonder drug’ from Japan: the human use perspective": https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3043740/
Chaga info: https://en.wikipedia.org/wiki/Inonotus_obliquus
Indirectly from quinine, most directly from hydroxychloroquine which itself is 3rd generation from quinine. This is based on research periods and U.S. Army Research lab developing hydroxychloroquine in the 50s-60s (suspected from "captured" German/Nazi tech on chloroquine), and then partnering with Merck in the 70s for the development of Ivermectin with a Japanese Partner. Still unclear how much USARL was directly involved, they may have just licensed the technology.
The partnership with Merck is noted in the Ivermectin document. If you dig a little you will find the USARL partnership with Merck via some sort of partnership or licensing in the early 70s, maybe 1971-73 timeframe.