Felis ISSN 2398-2950

Toxoplasma antibody titer

Contributor(s): Vetstream Ltd, Kerry Simpson

Overview

  • Enzyme-linked immunosorbent assay now most commonly used, available for IgG and IgM.
  • Other tests: indirect immunofluorescence, modified agglutination, indirect hemagglutination, latex agglutination, fecal flotation and polymerase chain reaction (PCR).
  • Single positive titer only indicates exposure, not recent or active infection (may persist for years).

Sampling

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Tests

Methodologies

  • Several:

ELISA - IgG  Enzyme linked immunosorbent assay (ELISA) 

  • Titer rises 10-28 days post infection, may persist for 6+ years.
  • Single high IgG titers do not necessarily suggest recent/active infection.
  • A rising titer (increasing by 4-fold) is suggestive of active/acute infection.
  • Failure to demonstrate a rising titer may occur if the titer is very high or has peaked prior to testing.
  • IgG may be negative in cats with toxoplasmosis.

ELISA - IgM

  • Titer rises 7-10 days post infection but often become negative after several months.
  • May remain elevated in cats with concurrent FIV Feline immunodeficiency virus disease or in ocular infections.
  • Higher positive predictive value than IgG for clinical toxoplasmosis.
  • Titers can rise with immune suppression/concurrent disease, so positive titer does not prove clinical toxoplasmosis.

PCR

  • Detects Toxoplasma DNA.
  • Detection of parasite in tissue relies on the presence of a tissue cyst in the aliquot.
  • Can be used on tissues, CSF, vitreous/aqueous humor, bronchoalveolar lavage, pleural, or peritoneal effusions. In addition, PCR can be used to assess fecal samples for shedding or to distinguish between similar protozoal parasites on samples which are positive on fecal flotation.

Indirect hemagglutination

  • Titer rises 22-30 days post infection.
  • Detects IgG to cytoplasmic antigen.
  • Failure to detect IgM means false negatives in reactivated or localized disease are more common.

Indirect immunofluorescence Indirect immunofluorescence

  • Titer rises 10-15 days post infection.
  • Measures attachment of antibody to Toxoplasma tachyzoites affixed to a slide.

Latex agglutination

  • Titer rises 14-21 days post infection.
  • Detects IgG and IgM (theorectically).
  • In one study was reported to rarely detect antibody in samples positive for only IgM.

Validity

Sensitivity

  • ELISA around 90% sensitive.

Specificity

  • Depends on test, eg theoretical possibility of false positives in autoimmune diseases.
  • Immunofluorescent assays more likely to give false negative results than ELISA.
  • PCR offers excellent specificity, but unproven sensitivity.

Technique (intrinsic) limitations

  • Young kittens may die before development of antibody.
  • Rate of antibody rise is often slow.
  • Antibody titers in chronic disease may be similar to normal cats.

Result Data

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Further Reading

Publications

Refereed papers

  • Recent references from VetMed Resource and PubMed.
  • Lappin M R & Powell C C (1991) Comparison of latex agglutination, indirect hemaaglutination and ELISA techniques for the detection of Toxoplasma gondii- specific antibodies in the serum of cats. JVIM 5, 299-301.
  • Lappin M R, Greene C E, Winston S et al (1989) Clinical feline toxoplasmosis - serological diagnosis and therapeutic management of 15 cases. JVIM 3, 139-143.
  • Wilson M et al (1990) Serologic aspects of toxoplasmosis. JAVMA 196, 277.

Other sources of information

  • Lappin M (1994) Diagnosis of Toxoplasmosis. In: Consultations in Feline Medicine 2nd Edition. Ed: August. W B Saunders Co, Philadelphia. pp 44-46.


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