Ask your vet perhaps, and we'll see if the others on the thread have actually been through strangles.... But I wouldn't work him if he has any symptoms still... Can he breathe? The symptom that he's not ready would be continued discharge and getting easily winded. You want to be careful, horses who get very sick with respiratory ailments have a hard time getting their wind back, you don't want to do any permanent damage.
the barn where I used to keep my horses had a case of strangles and the vet quaratined the place for a month, I think it was. Gates locked, only people with one of those gate cards could get through.
No personal experience with strangles, though. Good luck. Cindy Dawg.