Glands under the jaw may become infected with any number of different strains of bacteria, one of which is the strangles bacteria. Because that bacteria is so likely to spread, it is often best to assume that a swollen gland may well be this type of infection, and isolate and treat accordingly, locking down the facility. This is why new horses moving into a barn are often isolated until it becomes apparent if they are carrying anything. If the barn the horse has moved into has had strangles recently, a new horse moving into the barn may have been infected by the barn. May also have come from the trailer of a commercial hauler who brought the horse there. Horses who have been exposed to areas where many horses come and go (auction facilities especially) can pick the bacteria up. It is a bacterium, not a virus, if it is strangles that you are worried about. Quarantine for a barn with strangles is extremely demanding, it’s not easy or simple.
Whether or not the infection is the strangles bacterium or a different bacterium, with a gland that is infected, it will get big, form a head like a great big pimple and break open and pus will spread. If it is not strangles, it is not infective to other horses, just messy. Hot epsom salt compresses will encourage the gland to break open and release the pressure. If you think it may be strangles, all this pus and dressings are infective, handling and disposing of compresses and pus must be done carefully. If it’s not strangles, it’s just pus.
Glands may also increase in size if the horse is harbouring a virus, fighting the viral infection. The virus may infect other horses, but is not strangles. Every barn has it’s own viruses that the long term residents are immune to, but new horses, especially young horses, are not immune to. Like a cold going around in a schoolyard. This sort of infection is classic at barns where horses come and go, and with decent management, the horses usually recover without issue. These are usually rhino or flu viruses. Good luck!
