Actually, it *was* an Avast problem.
I clicked on the Avast icon in the upper right corner of the page and saw that "Automatic blocking of trackers" was ENABLED. (Facebook, Pinterest, Disqus were all blocked as well). I clicked on "ENABLED" and it changed to DISABLED. I then had an option to Block each of the four social media entries individually. I refreshed my page and, voila, I got Disqus back.
Luckily, I didn't take your assurance that Avast was not the problem seriously, otherwise I might never have found the problem.