Germs won’t live long in a harmonica. It’s too dry for anything to thrive. There should be no danger in playing it. If it looks all right I wouldn’t mind it myself, but many are repelled by the thought.
Also, you could just try cleaning it if you want to. After all, you did buy it in a thrift shop. It’s not like you are going to loose anything 
Have a look at this video: HOHNER Service Workshops:C02 - Cleaning - YouTube
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