My barn came down with strangles earlier this year, but there was no quarantining or disinfecting or vet visits, unfortunately (not to worry, I'm leaving). Very unprepared and poor management of the bacteria. This, in itself, caused the infectious period to last for a very long time, because once one horse got it, the entire barn had to get it, plus more horses were brought in, which kept it alive and well on the property. Anywho, with our poorly managed bought of strangles in our 20 horse barn, it lasted about 3 months, until new horses didn't come down with it once they entered the property.
Also, horse_r_life, bastard strangles is not the infection of the lungs. My horse was the only horse in the barn to get bastard strangles
, and almost died from it :(, and it took an extra two months of penicillin injections everyday and broad spectrum antibiotic powder to save her. Bastard strangles is actually the spread of the bacteria to lymph nodes that are in the rest of the body, and not only in the throatlatch/chin/face area. My horse had a lymph node that abcessed in her gut, that the vet estimated was larger than a soccer ball, when it was normally quarter-sized.
It was a terrible experience, and I hope you're barn does a better job at keeping the horses well. You'll probably be out of it within a month, without complications.
ETA - What you heard is partially correct. If the wounds under the chin have healed and are no longer dripping pus, AND the nose is dry and no longer runny, then the horse is for the most part!
no longer contagious. Unfortunately, they will continue to shed bacteria for a time after the obvious fluid has dried up. In most cases, they'll shed the bacteria for about 4-6 weeks after the wounds have healed and the nose stops dripping, but it's been known in some herds for the bacteria to shed for up to a year. It really is a toss up. Also, the horses will probably be fine to ride once the wounds are healed and the nose stops dripping and they've begun to eat normally again. HOWEVER, if they start acting unusual again, I.e. Going off their feed, not drinking water, fatigued, then CALL YOUR VET. The sooner you discover bastard strangles or any other complications, the better the chances are that your horse will survive them.