Glad to hear all is well. To answer your question "can you get a virus on an external hard drive, the answer is yes you can. It could have been in a file that you backed up to the external.
The good news is that you can scan external hard drives just as you would the one in your computer. Just point the scanning software at the connected external device and let it do it's thing.
Don't be a stranger on the site. Lots of good stuff in the Tutorals Section for almost anyone.