The vet feels that he has a neck injury (maybe he was choked???) and he has two abcessed teeth (he was unable to eat at the shelter). (gsgsrescue.org)
Also, the worst cases of mastitis I've ever seen were in nursing mothers who had cracked nipples, a perfect entry portal for bacteria [ditto breast abcesses] (skepticalob.com)
Crowns, fillings and root canals can cause a systemic abcess. (askdrhelen.com)