And the Latin plural is viri.

Anyway, Latin already had a word viri, but it was the nominative plural not of virus (slime, poison, or venom), but of vir (man), which as it turns out is also a 2nd declension noun. I do not believe that writers of English who write viri are intentionally speaking of men. And although there actually is a viri form for virus, it's the genitive singular, not the nominative plural. And we certainly don't grab for genitive singulars for the plurals when we've started out with a nominative. Such hanky panky would certainly get you talked about, and probably your hand slapped as well.