A generalized allergic reaction called serum
sickness is caused by an injection of serum or serum proteins from one species
of
animal into another. The immune system of the recipient reacts against it, producing an illness characterized by itching, fever, joint pain, skin eruptions, and extensive swelling (edema). Serum
sickness was more common in the past, when certain bacterial infections were treated with animal serums, than today, when antibiotics have mainly replaced serums.