- Complete panel for identification of the infection to Toxoplasmosis.
- Significant sensitivity of the IgG test allows to evaluate the seroconversion followup.
- The Avidity assay can be run in the early stage of acute infection due to the high sensitivity of the IgG test
The Toxo IgG Avidity test is a chemiluminescent immunoassay (CLIA), for use on IDS automated analyzers, for determination of Avidity Index of specific IgG class antibodies directed against the Toxoplasma gondii (Toxo) in samples of human serum or plasma (K3-EDTA, Sodium Citrate).
The possibility of differentiating antibodies at high avidity from low avidity allows to supply interesting clinical information. This assay is used as a diagnostic aid when assessing immunity status of patients related to Toxoplasmosis.
Toxoplasmosis is a parasitic disease caused by infection with the obligate intracellular protozoan Toxoplasma gondii1. Cats are the primary source of infection to human hosts, although contact with raw meat, especially pork, is a more significant source of human infections in some countries. Fecal contamination of hands is a significant risk factor 3.
Toxoplasmosis is one of the most chronic infections affecting one third of the world’s human population4. The prevalence of Toxoplasma gondii infection varies among different geographical regions. The infection is characterized by non-specific symptoms with the consequent formation of cysts that may remain in latent form in many organs5.
There are four groups of individuals in whom the diagnosis of toxoplasmosis is most critical: pregnant women who acquire their infection during gestation, fetuses and newborns who are congenitally infected, immune compromised patients, and those with chorioretinitis7,8,9. Infections in pregnant women can cause serious health problems in the fetus if the parasites are transmitted (i.e., congenital toxoplasmosis) and cause severe sequelae in the infant including mental retardation, blindness and epilepsy.
The use of serologic tests for demonstration of specific antibody to Toxoplasma gondii is the initial and primary method of diagnosis. Serological screening relies on IgG and IgM antibody determinations. The presence of elevated levels of Toxoplasma specific antibodies indicates infection has occurred at some point, but does not distinguish between an infection acquired recently and one acquired in the distant past. In acute infection, IgG and IgM antibodies generally rise 1 to 2 weeks of infection10. Detection of Toxoplasma specific IgM antibodies is so used as an aid in determining the time of infection, but it is critical to remind that IgM antibodies have been reported to persist for up to 18 months post infection11.
To differentiate between a recently acquired infection and a past infection, IgM and IgG positive specimens should be tested for IgG avidity. A high avidity index for IgG antibodies is a strong indication that an infection took place more than 4-5 months ago12,13,14.
- Ryan KJ; Ray CG ( editors ) ( 2004 ). Sherris Medical Microbiology ( 4th ). McGraw Hill. pp 723-7. ISBN 0838585299.
- Jones JL et al. Congenital Toxoplasmosis : A Review. CME Review Article Vol. 56, Number 5 2001 ; 296-305.
- Torda A ( 2001 ). “ Toxoplasmosis. Are cats really the source ? “. Aust Fam Physician 30 (8): 743-7. PMID 11681144
- Jones JL, Kruszon-Moran D, Wilson M, McQuillan G, Navin T, McAuley JB : Toxoplasma gondii infection in the United States : seroprevalence and risk factors. Am J Epidemiol 2001; 154; ( 4 ); 357-65.
- Guerina NG, Hsu HW, Meissner HC, Maguire JH, Lynfield R, Stechenberg B, et al. : Neonatal serologic screening and early treatment for congenital Toxoplasma gondii The New England Regional Toxoplasma Working Group. N Engl J Med 1994;330,(26 ); 1858-63.
- Montoya JG, Liesenfeld O ( 2004 ) Toxoplasmosis. Lancet,363: 1965-76.
- Montoya JG : Laboratory diagnosis of Toxoplasma gondii infection and toxoplasmosis. J Infect Dis 2002; 185 Suppl 1; S73-82.
- Remington JS, McLeod R, Thulliez P, Desmonts G ( 2001 ) Toxoplasmosis, p. 205-346. In J.S. Remington and Klein ( ed. ), Infectious diseases of the fetus and newborn infant,5th W.B. Saunders, Philadelphia,Pa.
- Thulliez P, Daffos F, Forestier f : Diagnosis of Toxoplasma infection in pregnant woman and the unborn child : current problems. Scand J Infect Dis Suppl 1992;84; ( 18-22).
- Montoya JG, Remington JS. Toxoplasma gondii. In : Mandel GL, Bennett JE, Dolin R, eds,Mandell, Douglas and Bennett ‘ Principles and Practice of Infectious Diseases,5thg Ed. Philadelphia : Churchill Livingstone,2000, pp 2858-2888.
- Wilson M, McAuley JM. Toxoplasma. In : Murray PR, Baron ES, Pfaller MA et al., eds. Manual of Clinical Microbiology, 7th Washington,DC : ASM Press,1999, pp 1374-1382.
- Hedman K, Lappalainen M, Seppaia I, Makela O: Recent primary toxoplasma infection indicated by a low avidity of specific IgG. J. Infect Dis 1989; 159, ( 4 ); 736-40.
- Montoya JG, Remington JS. Studies on the serodiagnosis of toxoplasmic lymphadenitis. Clin Infect Dis 1995; 20; ( 4 ) ; 781-9.
- Jenun PA, Stray-Pedersen B, Gundersen AG: Improved diagnosis of primary Toxoplasma gondii infection in early pregnancy by determination of anti-toxoplasma immunoglobulin G avidity. J Clin Microbiol 1997; 35; ( 8 ) 1972-7.