Also, many horse serum antitoxins have been refined of the antigenic components that cause serum sickness. Products derived from human serum have replaced the most frequently used antitoxins, which are rabies and tetanus horse serum antitoxins. The frequency and severity of reactions were directly related to the amount and type of antiserum administered. Symptoms usually last 1-2 weeks before spontaneously subsiding. Long-lasting sequelae generally do not occur.
Fatalities are rare and usually are due to continued administration of the antigen.
Primary serum sickness occurs 6-21 days after the administration of the inciting antigen. The onset may be more rapid with subsequent exposures to the same antigen, with symptoms occurring 1-4 days after exposure. The classic clinical manifestations consist of fever, arthralgia, lymphadenopathy, and skin eruption. Pain, pruritus, and erythematous swelling at the injection site usually precede the onset of disease. Patients also may report joint and muscle aches, chest pain, and difficulty breathing.