How do I scan android internal memory for viruses?
Yes, if a virus is programmed with the intention to spread widely to other devices, it certainly can copy itself to any connected media.
A good antivirus can scan MTP devices (like your phone) and spot a potential virus (at least my AV does).
It depends on the virus itself.
In the worst case, if you have a rooted device, debugging mode activated and allowed adb to connect without asking, a virus could infect your private applications data.
In the, more or less, best case it could only steal or destroy photos, videos, documents etc, but no messages from apps like Telegram.