When to worry:
Anaphylaxis is an emergency and must be seen immediately by a vet. Often the reaction occurs in the vet clinic (sometimes within seconds of vaccination) or soon after the animal has left the clinic, although it can take up to 24 hours to manifest (so you should keep a close eye on the animal at home). The vet will usually rush the dog straight out to a treatment room, where it will receive oxygen, IV fluids, anti-histamines, adrenaline, anti-inflammatories and sometimes other drugs to aid in the treating of low blood pressure.
Characteristically, delayed hypersensitivity reactions to tuberculin begin at 5 to 6 hours, are maximal at 48 to 72 hours and subside over a period of days. The resultant immune response consists of induration due to cell infiltration and occasionally vesiculation and necrosis . Clinically, a delayed hypersensitivity reaction to tuberculin is a manifestation of previous infection with M tuberculosis or a variety of non-tuberculosis bacteria. In most cases sensitization is induced by natural mycobacterial infection or by vaccination with BCG Vaccine.