Nobody AFAIK ever claimed “viruses” (or even “pizzas”) was not English—not people who study them, not any English dictionary, nor I.
The only fast rule is, as has been said, if you are going to pepper your prose with gratuitous foreign phrases, be sure to get it right. (And as far as medicine goes, imo one should be as clear as possible to avoid potential catastrophic screw-ups, though Latin still seems to be used to some extent in medical prescriptions.)
Back when I was in college, my fellow students thought they were so clever in realizing that the plural of syllabus could be syllabi and they used it constantly, mostly in the singular, as in “Don’t forget to take a syllabi.” Idiots.
Most people I know do say paparazzo/a, and graffito.
The one that gets me is “barista.” I have no problem with “baristas.” But should men with this job really be a “barista” with an -a? Or is this just the nature of loan words?
And “panini.” It kind of irks me that a word that just means “sandwiches” has this more particular meaning. Same with “chai.” It just means “tea,” nothing more than that.
Regarding “panini,” it somewhat annoys me that a word that simply means “sandwiches” ends up in a phrase like “sandwiches and paninis,” as if they’re too different things. It’s like “chai.” It just means “tea,” nothing more specific than that.
On the other hand… Italians use the English word ‘toast’ to mean a toasted sandwich. :D
And when a Frenchman refers to ‘des baskets’, he means sneakers (US) or trainers (UK).
And here’s A quick guide to speaking Franglais
I dare say speakers of many other languages misuse English words more than English speakers misuse words in their languages.
Koreans use the English word “toast” (토스트/to-seu-teo) to mean “grilled cheese sandwich”. They’ve upped the game on that though, as you can see on one outfit’s menu here.
Koreans also use the English word “white shirt” (화이트 셔츠/hwa-i-teu shye-cheu) to mean “dress shirt”, regardless of color or pattern of the shirt.
If you really want this thread to be effective, probably should have included “Viruses” in either the subject or first sentence. Write like an educator and not a magazine writer. You kind of buried the correct pluralization.