Recent primary toxoplasma infection indicated by a low avidity of specific IgG

J Infect Dis. 1989 Apr;159(4):736-40. doi: 10.1093/infdis/159.4.736.


An unusual assay was developed for the serologic diagnosis of recent primary infection by Toxoplasma gondii. This test measures the antigen-binding avidity of toxoplasma-specific IgG antibodies. Serum samples from 5 patients with recent primary toxoplasma infection were compared with those from 21 subjects with preexisting toxoplasma immunity. Patients with primary infection exhibited a low avidity of toxoplasma-specific IgG, which persisted for several months after the onset of symptoms of toxoplasmosis. In contrast, all subjects with past immunity had a high avidity of toxoplasma-IgG. This IgG avidity assay should assist in the diagnosis of acquired toxoplasmosis and may be used to identify pregnancies that are at risk for congenital toxoplasmosis.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Animals
  • Antibodies, Protozoan / immunology
  • Antibody Affinity*
  • Antibody Specificity
  • Antigens, Protozoan / immunology*
  • Child
  • Child, Preschool
  • Enzyme-Linked Immunosorbent Assay
  • Humans
  • Immune Sera / immunology
  • Immunoglobulin G / immunology*
  • Recurrence
  • Toxoplasma / immunology*
  • Toxoplasmosis / diagnosis*
  • Toxoplasmosis / immunology


  • Antibodies, Protozoan
  • Antigens, Protozoan
  • Immune Sera
  • Immunoglobulin G