What is serum sickness?

Serum sickness is a reaction of the immune system against proteins contained in antiserum from a non-human animal.

Antisera are based on the same principles as vaccines, but instead of inducing immunity in the patient, it is induced in a host animal and the immunized serum is subsequently transfused. Antisera are primarily used to treat poisonous bites and stings.

Serum sickness can be understood as a delayed hypersensitivity reaction, since its symptoms appear several days after exposure and can be delayed for several weeks.

Specifically, serum sickness is classified as a type III hypersensitivity reaction which is caused by the accumulation of antigen-antibody complexes that have not been properly cleared by the cells of the immune system.


The symptoms produced by serum sickness take several days to appear, usually between 5 and 10 days, although it can take several weeks, there are even cases that take longer than 1 month.

Most symptoms are common to hypersensitivity reactions and infections, including:

Dermatitis and epidermal efflorescence itching Joint pain Fever Lymphadenopathy Discomfort Hypotension Splenomegaly Glomerulonephritis Proteinuria blood in urine Shock


Antisera or immune sera are blood serum preparations and polyclonal antibodies that are used as passive immunity therapy in numerous diseases.

When an antiserum is administered, the recipient’s immune system can recognize the proteins contained in the serum as harmful antigens and produce antibodies against them.

Antibodies bind to proteins and form so-called immune complexes, which are insoluble and precipitate on the walls of blood vessels and activate the complement cascade.

With the activation of the complement system, an inflammatory response and consumption of C3 (complement component 3). The result is vasculitis and hypocomplementemia, producing the typical symptoms of serum sickness.

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Serum sickness is also associated with antitoxins and some drugs such as allopurinol, barbiturates, captopril or cephalosporins among others.


By removing exposure to the triggering agents, symptoms usually resolve within 4-5 days. While they remit, they can be controlled with corticosteroids, antihistamines, and pain relievers.

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