In reply to:
Found this, though, in Notre Dame's on line Latin Dictionary. It's probably as authorative as we're going to get:
virus -i n. [slimy liquid , slime; poison, esp. of snakes, venom; any harsh taste or smell].
So it's second dec, and it's masculine more likely than not. Phew!
I think you may find that n. stands for neuter rather than noun. That is how I would read the similar entry in Perseus' Lewis and Short (http://makeashorterlink.com/?N152524C6)anyway.
The article max referred us to suggests that the plural is unattested in Latin, and it is fair to say that it is a matter of some controversy how the Romans would have formed the plural had they ever had call to use it.
I do not see, therefore, that there is anything to criticise in using the normal English way of forming plurals by adding -es. This is the best policy anyway in pluralising naturalised English words. I doubt anyone would pluralise gamelan as gamelan-gamelan, though this is what it would be in the language it was borrowed from.
Bingley
