Evaluation of serological markers for the immunodiagnosis of acute acquired toxoplasmosis

Abstract

The detection of speci®c IgM antibodies has been the most frequently used serological marker for diagnosing recent toxoplasmosis. However, the persistence of speci®c IgM antibodies in some patients and the use of tests with a low speci®city have complicated the interpretation of serological results when toxoplasmosis is suspected. The purpose of the present study was to determine the value of newer serological techniques in the diagnosis of acute acquired toxoplasmosis. Sixty-four sera, 31 from patients with Toxoplasma gondii infection and 33 from patients with latent infection, were tested. Anti-T. gondii IgA was measured by two antibody capture ELISA tests (Platelia 1 Toxo IgA and ETI-TOXOK A) and an automated direct ELISA (IMx 1 Toxo IgA); all three assays detected antibody levels compatible with a recent infection in sera from all 31 patients with acute toxoplasmosis. However, signi®cant levels of IgA were also detected with high frequency by all three assays in sera from patients with latent infection. IgE antibodies detected by IgE immunosorbent agglutination assay (ISAGA) were present in 26 (84%) of 31 patients with acute toxoplasmosis and in sera from two subjects with latent infection taken >1 year after the beginning of the clinical symptoms of infection. Thirty (97%) of 31 patients with a recent T. gondii infection and 15 (45%) of 33 subjects with latent infection had an AC/HS pattern compatible with acute toxoplasmosis. The avidity of T. gondii IgG was evaluated by two methods. One method was based on the titration of each serum sample and calculation of the titres, in the absence and presence of urea, in relation to a de®ned cut-off value. In the other method, a single serum dilution was used and the absorbances of the reactions in the presence and absence of urea were compared. The titration method was more sensitive for diagnosing recent primary infection; all 31 sera from patients with acute toxoplasmosis had avidity indices compatible with acute toxoplasmosis by the titration method, whereas with the single dilution method, sera from four patients had equivocal results. In the 33 individuals with latent infection, similar results were obtained with the two avidity methods; only one serum sample had a non-compatible avidity value with the titration method. The results obtained in the present study show that the current serological markers used for diagnosing acute acquired toxoplasmosis have signi®cant limitations. The data suggest that determination of the avidity of T. gondii-speci®c IgG by the titration method in patients with detectable IgM antibodies de®nes most accurately the stage of infection by T. gondii.

Kinetics and time dependence of the differential agglutination of acetone [AC]- and formalin [HS]-fixed Toxoplasma tachyzoites by serum of mice with experimental toxoplasmosis

“…Both tests had low values at the early time of infection (HS \100 IU/ml and AC, 50 IU/ml) then both values increased to attain plateau level. In the present study, the AC titer attained high level early in the infection being caused by the proliferating tachyzoites (Montoya and Remington 1995;Suzuki et al 2001;Montoya et al 2007). On the other hand, the HS-test still rises up late, as previously reported in humans where high HS-titers are characterizing chronic infections (Suzuki et al 1988;Dannemann et al 1990;Montoya et al 2007).…”

“…The Toxoplasma agglutination test is very simple, rapid and does not require special technique to prepare the antigen neither special equipments nor apparatus to be carried on (Suzuki et al 2001). The use of sensitive antigenic preparation and adding 2-Mercaptoethanol improves its specificity and sensitivity, to parallel those of the dye test (Desmonts and Remington 1980).…”

“…The differential agglutination test (AC/HS) compares the titers obtained with acetone-fixed tachyzoites (AC-antigen) with those obtained with formalin-fixed tachyzoites (HS-antigen) (Suzuki et al 1988(Suzuki et al , 2001. The results are expressed as having equivocal, acute or nonacute patterns depending on the relation between the titers obtained in the AC-test and the HS-test and their location of the AC/HS fraction on a chart (Fig.…”

Serology using rROP2 antigen in the diagnostic of toxoplasmosis in pregnant women

“…Some serological tests use live agents (Sabin Feldman assay), intact parasites, as indirect immunofluorescence assays or whole extracts in enzymatic immunosorbent assays to detect the presence of specific IgM for definition of acute (less than one year) infections during screening for treatment (REMINGTON et al, 2006). The development of commercial assays and the use of ultra-sensitive techniques such as IgM capture tests increased the sensitivity of these assays, but resulted in extended periods of IgM presence after acute infections, with consequent loss of screening efficiency (SUZUKI et al, 2001). IgG avidity was introduced for temporal definition of viral infection in rubella (LEHTONEN & MEURMAN, 1982), and was adapted to toxoplasmosis to distinguish recent and old infections (HEDMAN et al, 1989).…”

“…Several studies have reported that the avidity of antibody IgG is a good index of the time of the infection, defining if the acute infection has occurred in the past few months despite conflicting results between tests (BARBERI et al, 2001). Recombinant antigens were frequently tested in serology for toxoplasmosis (SUZUKI et al, 2001), usually with adequate but weak screening results compared to whole extracts in ELISA ( VAN GELDER et al, 1993 (BEGHETTO et al, 2003). Most of these studies were performed on selected sera panels defined by other tests, which could interfere in efficacy determination.…”