The relationship and significance of antibody titres as determined by various serological methods in glandular and ocular toxoplasmosis

Evaluation of IFA, MAT, ELISAs and immunoblotting for the detection of anti-Toxoplasma gondii antibodies in paired serum and aqueous humour samples from experimentally infected pigs

The study evaluated the efficiency of diagnostic laboratory methods to detect anti-Toxoplasma gondii antibodies in paired serum and aqueous humour samples from experimentally infected pigs. 18-mixed breed pigs were used during the experiment; these were divided into two groups, G1 (infected group, n=10) and G2 (uninfected group, n=8). Infection was performed with 4 x 10(4) VEG strain oocysts at day 0 by the oral route in G1 animals. All pigs were euthanized at day 60, when retina, aqueous humour, and blood samples were collected. Anti-T. gondii antibody levels were assessed in serum (s) and aqueous humour (ah) by indirect immunofluorescence assay (IFA), modified agglutination test (MAT), m-ELISA (using crude membranes from T. gondii tachyzoites as antigen) and r-ELISA (using rhoptries from T. gondii tachyzoites as antigen). Polymerase chain reactions (PCR) of samples from the retina were performed by using Tox4 and Tox5 primers. Antibody titers of G1 animals ranged from 128 to 1024 and from 16 to 256 in serum and aqueous humour, respectively. There were differences in the correlation coefficients between IFA(s) x IFA (ah) (r=0.62, P=0.05), MAT(s) x MAT (ah) (r=0.97, P<0.0001); however, there was no significant difference between r-ELISA(s) x r-ELISA (ah) (r= 0.14, P=0.7). Antibodies present in serum and aqueous humour recognized similar antigens. Samples of retina were positive by PCR in 30% (3/10) of infected pigs. G2 animals remained without antibody levels and were PCR negative throughout the experiment. These results suggest that the use of a combination of tests and immunoblotting for paired aqueous humour and serum samples could improve the sensitivity and specificity for the diagnosis of ocular toxoplasmosis.

Utility of tissue culture for detection of Toxoplasma gondii in vitreous humor of patients diagnosed with toxoplasmic retinochoroiditis

Laboratory recovery and confirmation of the etiologic agent in necrotizing retinochoroiditis are problematic. Tissue culture and intraocular antibody titers were compared as adjuncts to clinical diagnosis for toxoplasmic retinochoroiditis: the correlations were 91 and 67%, respectively. Isolation of Toxoplasma gondii may establish a definitive diagnosis in patients with toxoplasmic retinochoroiditis.

Development of specific immunoglobulins G, M, and A following primary Toxoplasma gondii infection in pregnant women

The development of specific antibodies following primary Toxoplasma gondii infection during pregnancy was assessed by six different antibody assays: dye test, Platelia Toxo-IgG, Toxo-Screen DA IgG, Platelia Toxo-IgM, Toxo-ISAGA IgM, and Platelia Toxo-IgA. A total of 126 sera from 27 pregnant women, for whom the time of acquisition of infection could be estimated fairly accurately, were included. All tests showed great individual variation in the peak amounts of antibodies detected. The times elapsed after infection until the peak was reached also varied greatly from individual to individual: the ranges were 2 to 21 weeks for the dye test, 4 to 36 weeks for Platelia Toxo-IgG, 4 to 30 weeks for Toxo-Screen DA IgG, 2 to 18 weeks for Platelia Toxo-IgM, 1 to 6 weeks for Toxo-ISAGA IgM, and 2 to 21 weeks for Platelia Toxo-IgA. In the early phase of the infection the dye test and the specific-IgM tests were the most sensitive. Toxo-Screen DA IgG was more sensitive than Platelia Toxo-IgG in the acute phase, while Platelia Toxo-IgA was clearly the least sensitive assay. Of the sera collected 21 to 52 weeks after infection, all were positive by the dye test, all except one (which was negative by Platelia Toxo-IgG) were positive by the specific-IgG tests, approximately 80% were positive by the IgM tests, and 45% were positive by the IgA test. Due to the great individual variation it seems impossible to estimate when the infection occurred based on results obtained from a single serum, and it may even be difficult to assess when a titer increase in paired sera is detectable unless the first sample is only marginally positive. As a diagnostic criterion a dye test titer of >/=300 IU/ml has a low sensitivity for recent primary infection.

Performance characteristics of a commercial antibody-capture enzyme immunoassay for detection of Toxoplasma-specific IgM antibodies

Antibody-capture enzyme immunoassay (EIA) for the detection of Toxoplasma-specific IgM has been shown to provide significantly higher specificity than the indirect IgM EIA. A new commercially available antibody-capture EIA (PLATELIA Toxo IgM EIA) converted 99 out of 100 false-positive Toxo-plasma IgM determinations to true negative. Experiments using Toxoplasma IgM calibrators demonstrated the antibody-capture EIA is approximately eightfold more sensitive than a new automated microparticle EIA for Toxoplasma IgM antibodies (IMX Toxo IgM EIA), and approximately equal in sensitivity to the indirect immunofluorescence assay. Precision studies of the antibody capture EIA using low, medium, and high calibrators gave coefficients of variation ranging from 3.0%-4.5% for within-run and 5.2%-11.4% for run-to-run variation experiments. Interference from high levels of bilirubin, albumin, hemoglobin, and lipid was not detected. Sera from patients with inflammatory or infectious disorders were tested for interference in the antibody-capture EIA. False-positive Toxoplasma IgM results were not observed, but low-level negative interference was detectable when patient sera was mixed with Toxoplasma-positive sera. Preparations of purified human IgM also produced negative interference in the antibody-capture EIA for Toxoplasma IgM.

Analysis by immunoblotting of Toxoplasma gondii exo-antigens and comparison with somatic antigens

Two soluble Toxoplasma gondii antigen preparations were compared using the immunoblotting technique. The first preparation, which is commonly employed in ELISA tests, corresponds to a lytic extract of the parasite. The second known as exo-antigen, has yielded good results in cell immunity research and is obtained from Toxoplasma gondii culture supernatants. In both preparations, components exhibiting same molecular weight of 57-52 (doublet), 43, 38, 35, 30 and 20 kDa were revealed. In addition, two major 27- and 78-kDa components were detected in exo-antigens. The 30 kDa protein was intensely recognised by all sera, confirming the advantage of its use as an antigen in serological reactions. Exo-antigens could be employed as a soluble antigenic solution because they are easy to obtain, they display good antigenicity and their antigenic composition has been defined. Moreover their preparation does not require mouse inoculation. An evaluation of the enzyme-linked immunosorbent assays (ELISAs) involving these antigens has yet to be performed.

Evaluation of ELISA for the detection of Toxoplasma antibodies in swine sera

Enzyme-linked immunosorbent assay (ELISA) is compared with the indirect fluorescent antibody test (IFAT), the indirect haemagglutination test (IHAT) and the latex agglutination (LA) test for the detection of toxoplasma antibodies in swine sera. The 100 swine sera examined represent ELISA values from greater than 0 to 154 EIU. The agreement was highest (0.67) between ELISA and IFAT with an ELISA cut-off value of 30 EIU, and between ELISA and the LA test with an ELISA cut-off value of 50 EIU (0.74). All sera giving less than 10 EIU were negative in the other tests, and all those with greater than 70 EIU were positive in 1, 2 or all of the reference tests. In order to avoid false positive results with ELISA, all sera giving 10-70 EIU should be confirmed with a test which has a good specificity, e.g. IFAT. ELISA is a sensitive test and is highly suitable for the screening of large amounts of samples, but it may be too complicated for screening toxoplasma antibodies in the laboratories of abattoirs.

Serologic investigations in a New York City cohort of parenteral drug users

Human immunodeficiency virus (HIV) infection continues to be a major health problem for society. Intravenous drug users are the second largest risk group for HIV infection. The disease primarily affects immunologic functioning. This study examined the inherent immunologic dysfunction by measuring the seroprevalence of infection against pathogens often associated with HIV infection. Additionally, chi square analysis was used to compare intravenous drug users with a non-drug-using control group to see if any difference existed in the prevalence of antinuclear antibody, rheumatoid factor, abnormal titer of antibody to Toxoplasma gondii, cytomegalovirus, and herpes simplex virus (types 1 and 2). The intravenous drug users had a significantly greater level of antibody titers for antinuclear antibody and Toxoplasma gondii than did controls. Abnormal serologic results were not significantly associated with HIV seropositivity. The findings of this study suggest that intravenous drug users experience a greater prevalence of alteration in serologic markers unrelated to HIV exposure.

Evaluation of ELISA for the detection of Toxoplasma antibodies in swine sera

Enzyme-linked immunosorbent assay (ELISA) is compared with the indirect fluorescent antibody test (IFAT), the indirect haemagglutination test (IHAT) and the latex agglutination (LA) test for the detection of toxoplasma antibodies in swine sera. The 100 swine sera examined represent ELISA values from greater than 0 to 154 EIU. The agreement was highest (0.67) between ELISA and IFAT with an ELISA cut-off value of 30 EIU, and between ELISA and the LA test with an ELISA cut-off value of 50 EIU (0.74). All sera giving less than 10 EIU were negative in the other tests, and all those with greater than 70 EIU were positive in 1, 2 or all of the reference tests. In order to avoid false positive results with ELISA, all sera giving 10-70 EIU should be confirmed with a test which has a good specificity, e.g. IFAT. ELISA is a sensitive test and is highly suitable for the screening of large amounts of samples, but it may be too complicated for screening toxoplasma antibodies in the laboratories of abattoirs.

A dot-ELISA intended for the specific and simultaneous detection of antibodies directed to antigens derived from Toxoplasma gondii, rubella virus, cytomegalovirus, and type 1 and type 2 herpesviruses

A procedure for the routine and simultaneous laboratory detection of IgG antibodies produced in humans in the course of various infectious diseases is described. The procedure, based on dot-enzyme-linked immunosorbent assay (ELISA), used single nitrocellulose strips onto which several antigens were dotted in close proximity. Optimal conditions were specified that allowed the unequivocal and simultaneous detection of IgG antibodies specifically directed against Toxoplasma gondii, rubella virus, cytomegalovirus, and herpes simplex virus type 1 and type 2 antigens. This technique has proved to be simultaneously specific, sensitive, and reliable, and it has been applied to prenatal screening of sera from pregnant women. It is suggested that this technique should also be used for the screening of large numbers of sera under field trial conditions.

Laboratory diagnosis of toxoplasmosis

Acute infection with Toxoplasma gondii is diagnosed by (i) detection of the parasite directly in patients' specimens using histological or immunological methods, (ii) isolation of T. gondii from blood, body fluids or tissue by inoculation in laboratory mice or on tissue culture cells, or (iii) serological methods for determination of a significant, T. gondii-specific, antibody titre rise or of T. gondii specific IgM (or IgA) antibody. Because of their high sensitivity, specificity and relative ease of performance, serological methods are preferentially used for diagnosis of T. gondii infection. The diagnosis of acute, postnatally-acquired, primary toxoplasmosis is usually established by serological methods and will in general present few problems. However, diagnosis of congenital infections and their late sequelae or of reactivation of a latent infection in immunocompromised patients is often more troublesome because of the absence of a significant antibody titre rise or the lack of specific IgM antibody. In these cases a combination of various methods may be required for definitive diagnosis of T. gondii infection.

Toxoplasmosis in sheep II. The ability of a live vaccine to prevent lamb losses after an intravenous challenge withToxoplasma gondii

Two-tooth ewes (n=48) were immunized pre-tupping with a live Toxoplasma gondii vaccine. At midpregnancy these ewes were challenged intravenously with 1 x 105 live T. gondii tachyzoites. The strain of T. gondii used for vaccination was an incomplete strain that did not produce oocysts. It was derived by continuous twice weekly passage in mice. The lambing percentage for ewes immunized with the live vaccine was significantly higher (P<0.001 normal score) than non-vaccinated control ewes. However, vaccination did not prevent foetal or placental infection. The serological response to vaccination and challenge was measured by both the Dye test and the Indirect Haemagglutination test. No significant relationship between titre of antibody and protection in the vaccinated ewes was observed.

A seroepidemiological survey of toxoplasmosis in Scotland and England

The Sabin-Feldman dye test was used to detect the presence of Toxoplasma antibodies in two groups of blood donors in central Scotland, one group from a rural area and one from an urban area, and in patients attending a medical outpatients clinic and females attending an antenatal clinic serving a mixed urban and rural area in the midlands of England. Results obtained from these four groups showed that 7.6, 7.8, 35.7 and 14.9% respectively had antibody titres of 1: greater than or equal to 10. A group of travelling people, defined in the Local Government and Planning (Scotland) Act, 1982, as '...persons of nomadic habit of life, whatever their race or origin...', from Scotland were also surveyed and 28% of this group had antibodies of 1: greater than or equal to 10. Individuals in this latter group were reported to have minimal contact with cats because of their lifestyles. The prevalences of the travelling people were analysed by age group and showed no correlation with age, but other groups did show an increasing prevalence with age. The significance of these results is discussed.

Antibody patterns in the serological diagnosis of acute lymphadenopathic toxoplasmosis

Sera from six patients at various stages of acute lymphadenopathic toxoplasmosis were tested using nine different types of test currently available for the serological diagnosis of the disease. A diagnosis was made on positive serology in three of the patients. The antibody patterns of two of these patients were studied over a period of six months and the third was studied over two months. A diagnosis was made on lymph node morphology in the other three cases. Two serum samples were tested from each of these patients. The results obtained suggest that a rationalisation of the types of test used should be encouraged and that an enzyme-linked immunosorbent assay (ELISA) for parasite-specific IgG and an antibody class capture ELISA for parasite-specific IgM are sufficient to confirm the diagnosis of acute lymphadenopathic toxoplasmosis.

Serologic and intradermal tests for parasitic infections

For years, the diagnosis of most parasitic diseases has depended upon the direct demonstration of the parasite or its cysts, eggs, or larvae in specimens. In some infections, direct demonstration of the causative agent or its stages is almost impossible. In such cases, indirect techniques, such as serologic methods, have been found to be more practical and sensitive than are direct methods. Most serologic methods have been devised to detect antibodies. Tests for the detection of antigen are just beginning to be utilized; however, the practicality and under what situations antigen detection tests can be used await further testing. The majority of the serum antibody tests employ a heterogeneous mixture of antigens. Antigens derived from whole adult or larval stages usually result in tests with poor specificity and/or sensitivity. The necessity for better purified and standardized antigens cannot be over emphasized. Although there have been many major advances in the serodiagnosis of parasitic infections, a major drawback to routine use of parasitic serologies is the lack of commercially available reliable test kits. For the diagnosis of most parasitic diseases, one must rely upon specialty laboratories or public health laboratories. Before any laboratory begins to offer parasitic test serologies, they should contact their local or state public health laboratory or the Parasitic Serologic Section of the Centers for Disease Control to determine the pros and cons of these tests. Information of this type should be used to inform the physician of the limitations of the test in the differential diagnosis.

Detection of specific IgG and IgM antibodies to Toxoplasma gondii with a commercially available enzyme immunoassay kit system

A total of 138 serum samples submitted for toxoplasma serology have been examined by enzyme immunoassay using kits produced by Labsystems Oy for the detection of specific antibodies of the IgG and IgM class. Results were compared with the dye test, an indirect haemagglutination test, and an indirect immunofluorescence test for specific IgM. The enzyme immunoassay was less sensitive than the dye test, but by running both IgG and IgM enzyme immunoassays, 92.4% sensitivity was achieved. The specificity of the enzyme immunoassay was good, with only one dye test negative serum giving a positive (but weak) IgG enzyme immunoassay reaction. Thirty serum samples from patients with no evidence of exposure to Toxoplasma gondii gave negative results in the IgM enzyme immunoassay. Enzyme immunoassay results were expressed in enzyme immunoassay units, as a percentage value of a standard serum. This convention will be of value in the direct comparison of assay systems and in the application of quality control procedures.

The antigenic structure of Toxoplasma gondii: a review

Even though T. gondii is ubiquitous in the animal kingdom, definitive information on its antigenic structure has only become available over the last few years, largely as a result of recent advances in immunology and biochemistry. New knowledge in this area will enable the immune response to the parasite to be studied in greater detail and may lead to the development of newer, more meaningful diagnostic tests for toxoplasmosis, and possibly a vaccine against it. This paper reviews knowledge on the antigenic structure of this extremely widespread and important protozoan parasite.

The prevalence of Toxoplasma gondii antibodies in man in Plateau State and meat animals in Nigeria

Toxoplasma gondii antibodies were found in the sera of 22.86% of people in the Jos area of Plateau State, Nigeria. The incidence of antibodies in Nigerian food animals was 17.40%, the highest being in sheep (21.92%) and lowest in goats (13.88%). Cattle and horses were roughly equally infected--about 17.0%. The zoonotic potential of T. gondii in food animals is stressed and epidemiological factors are reviewed.

Antigen specific lymphocyte transformation induced by secreted antigens from Toxoplasma gondii

Secreted (TSA) and water lysed (WLA) antigens derived from cell culture of the RH strain of Toxoplasma gondii have been used to induce antigen specific mitogenesis of lymphocytes from patients with symptomatic and asymptomatic toxoplasmosis. Lymphocyte responsiveness to WLA was similar to previous reports, with about 50% of patients showing a false negative reaction. Responses to TSA however were highly specific, with no false negative reactions. This increased specificity was not due to an increased response against TSA by patients' lymphocytes (P less than 0.001), but a lower TSA response by uninfected subjects' lymphocytes (P greater than 0.1) compared with WLA in both cases. In a minority of both infected and uninfected subjects, there was a low but detectable response to antigens secreted by the host cell line (HCA), and this was directly compared to their responses against TSA. There was at least a 10-fold increase in the patients' responses to TSA when compared with HCA (P less than 0.001), whereas there was no significant difference between the uninfected subjects' responses to these antigens (P greater than 0.1). Preliminary observations have suggested that TSA is distinct from other defined secreted antigens as both heat treatment and solid phase immunosorption did not have any noticeable effect on TSA-induced mitogenesis.

Comparison of a latex agglutination test with other serological tests for the measurement of antibodies to Toxoplasma gondii

One hundred sera from 49 patients with glandular toxoplasmosis were examined by a latex agglutination test, the dye test, an indirect haemagglutination test, and a double antibody sandwich enzyme linked immunosorbent assay (ELISA) for antitoxoplasma IgM. The results support previous findings that the dye test, indirect haemagglutination test, and latex agglutination test measure different antibodies to Toxoplasma gondii. In early glandular toxoplasmosis, when specific IgM was detected, the titres of both the latex agglutination test and the indirect haemagglutination test were lower than the dye test. Repeat specimens from 11 of the patients showed four cases in which the latex agglutination test titres never exceeded 1/256, whereas both the dye test and the indirect haemagglutination test showed significant titres and specific IgM was detected in every case. We conclude that the latex agglutination test should not be used as a substitute for the dye test in the serological diagnosis of glandular toxoplasmosis. All sera giving a positive latex agglutination test result should be referred for further tests. A combination of the dye test and double antibody sandwich ELISA gives the most reliable serological diagnosis of early glandular toxoplasmosis.

Does Toxoplasma cause polymyositis? Report of a case of polymyositis associated with toxoplasmosis and a critical review of the literature

We report here a case of polymyositis and toxoplasmosis, and review the previous examples of this association. We suggest that in most cases this relationship is due to reactivation of latent infection in an immunocompromised host. Gross immunological aberrations underline the pathogenesis of polymyositis and these predispose the patient to the development of toxoplasmosis. Anti-protozoal therapy is necessary and produces some clinical benefit, but it does not cure the polymyositis.

Ultrastructural and biochemical studies on the immunohistochemistry of Toxoplasma gondii antigens using monoclonal antibodies

To determine the cellular distribution of Toxoplasma antigens, RH strain tachyzoites were incubated with either one of three monoclonal antibodies (FMC 19, FMC 20, FMC 22) to T. gondii, or one of two controls (the murine myeloma protein MOPC 21, or phosphate buffered saline), and then incubated with peroxidase-labelled goat-antimouse IgG. Diaminobenzidine was added as substrate and electron microscopy was used to localize the reaction. All three antibodies bound to the entire periphery of the tachyzoite surface membrane. To ascertain the chemical composition of the antigens against which seven monoclonal antibodies (FMC 18, FMC 19, FMC 20, FMC 22, FMC 23, 2G11, 3E6) to T. gondii reacted, untreated, pronase-treated, or periodate-treated tachyzoites were incubated with the antibodies or MOPC 21, and then with [125I]-Protein A. The pronase-treated tachyzoites showed reduced binding for six of the antibodies, compared with the reduction in binding of MOPC 21 with the pronase-treated parasites. The periodate-treated tachyzoites had reduced binding for FMC 18 only. The results of these experiments confirm that most Toxoplasma surface antigens are protein in nature, and are consistent with the hypothesis that at least one cytoplasmic antigen is secreted onto the parasite cell surface.

A new soluble antigen preparation of Toxoplasma gondii and its use in serological diagnosis

A new method of solubilizing Toxoplasma gondii in 5% saponin and 5% octyl glucoside in combination (S-Ag) is described. When analysed by IEP, seven antigens could be detected. Four of these antigens (Ag 1, 2, 3 and 12) were shown by 125I-iodination to be of membrane origin. The remaining three (Ag 4, 5 and 6) were shown to be of intracellular origin and comprise the antigenic profile of more conventional preparations used in serodiagnosis. The S-Ag preparation was tested by ELISA (S-ELISA) in parallel with a freeze-thaw preparation containing only Ag 4, 5 and 6 (FT-ELISA), against the IgG-IFAT. The regression of the FT-ELISA against the IgG-IFAT was poor and there was a high incidence (28.9%) of false negative results. A second order polynomial provided a better fit and this predicted FT negative results on sera with IgG-IFAT titres lower than 1:1024. From this titre upwards, the test was specific but insensitive. The S-ELISA was more specific (5.6% false negatives) and more sensitive; polynomial terms could not provide a better fit. The improvement in the test using the S-Ag is considered to be due to the additional membrane antigens. The possible role of this solubilized antigen in future serodiagnosis is discussed.

Toxoplasma, Toxocara, and epilepsy

The presence of positive antibody titres to Toxoplasma and Toxocara in an adult epileptic population has been examined in relation to other observations of aetiological importance. With Toxoplasma, and more particularly with Toxocara, a higher incidence of positive antibody titres was recorded than in nonepileptic populations. Comparison with previous studies in childhood epilepsy indicate that the incidence of positive titres increased with age throughout adult life. Despite attention to the age of onset of epilepsy, presumed aetiological factors, and electroencephalographic and clinical observations, no causal relationship between parasitic infection and the aetiology of epilepsy was established.

An investigation of the antigenic structure of Toxoplasma gondii

Mechanical fragmentation has been the prime method for preparing soluble Toxoplasma gondii antigens for use in serodiagnosis. The three methods most commonly used (lysis-in-water, sonication and freeze-thawing) all yielded three antigenic peaks (4, 5 and 6) on crossed immunoelectrophoresis. Antigen 6 has been shown to be heat stable (56 degrees C/1 h) and appears to be a major antigen in the indirect haemagglutination test (IHAT). Saponin and octyl glucoside were found to be the most effective detergents for solubilization when used in combination, yielding between 7 and 11 antigens. Using a new triple-staining technique, antigen 3 has been characterized as a glycoprotein, antigen 7 as a lipopolysacchiaride and antigens 1, 2, 4, 5, 6 and 8 to 11 as proteins. Molecular weight determination by gel filtration has been carried out and the majority of the antigens have a mol. wt of 10(5) to 1.5 x 10(5) daltons. Crossed immunoelectrofocusing has shown that all the antigens are isoelectric at acidic pH. The findings of this preliminary investigation into the basic antigenic structure of T. gondii are discussed in relation to future work and the rational development of serodiagnostic tests.

Screening for toxoplasmosis in pregnancy

The prevalence of antibody against Toxoplasma gondi in a population of 715 pregnant women has been evaluated by two methods: indirect haemagglutination antibody (IHA) and indirect fluorescent antibody (IFA) test and all positive sera were checked by the dye test. Five hundred of the study population were questioned on diet and on animal contact to elucidate a possible relation to the prevalence of antibody. Results are expressed in international units (IU) of antibody against T gondi. Of the 715 sera, 171 were positive by IHA and 173 by IFA. One hundred and sixty-seven sera were positive by both tests, ninety-eight (58%) correlating exactly, as to the concentration of antibody. The ten sera which were not positive by both tests all had detectable antibody at the minimum concentration only (12 IU). The dye test confirmed all sera positive by both tests with the exception of three. It also confirmed one of four sera positive by IHA antibody alone and two of six positive by IFA alone. All sera that proved dye test-negative had low antibody concentrations (12 IU) by IHA or IFA. The IHA test, which is commercially available in kit form, would be suitable for use as a screening test during pregnancy. The estimated annual rate of antibody acquisition over the age range 16-40 years is 1.2% per annum with the highest rate in the 36-40 age group (2.5% per annum) and the lowest in the 26-30 age group (0.4% per annum). The clinical history was not significantly different between those with and those without antibody against T gondi but significantly more women in the 36-40 age group had a history of animal contact than those in the 26-30 age group. No conclusive evidence of recent or current infection was found.

Reverse enzyme immunoassay for detection of specific anti-Toxoplasma immunoglobulin M antibodies

A reverse enzyme immunoassay (R-EIA) is described, in which polystyrene muplates are sensitized with anti-immunoglobulin M (IgM) (mu chain) antibodies and then sequentially allowed to react with patient's serum, peroxidase-labeled Toxoplasma gondii soluble antigen, and substrate. Measurement of activity of the solid-phase bound enzyme conjugate was done by colorimetric reading of the final developed color and kinetically by the initial rate of color development. This R-EIA allowed full resolution between absorbance values of a group of 36 sera which presented positive results in the Toxoplasma IgM immunofluorescence test and the remaining groups, which consisted of 39 normal individuals, 22 rheumatoid factor-positive sera, 8 Waldenstrom's macroglobulinemic sera, 3 infectious mononucleosis samples, and 6 high-titered IgG anti-T. gondii sera. No interference of rheumatoid factor IgM or inhibition by high-titered specific IgG was detected, even in the false IgM immunofluorescence-positive rheumatoid factor samples. Likewise, false-negative IgM immunofluorescence samples gave positive R-EIA even without adsorption with Staphylococcus aureus protein A. The possibility of direct tagging of the antigen with the enzyme eliminates the need for using antigen and anti-antigen conjugates as separate layers, therefore eliminating one step in the assay.

A standardized enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies to Toxoplasma gondii

An enzyme-linked immunosorbent assay (ELISA) for the serodiagnosis of Toxoplasma gondii infections on single serum dilutions was developed. This test system is a standardized kit designed to detect circulating specific antibodies to Toxoplasma gondii in human sera. It consists of Toxoplasma gondii soluble antigen-coated microtitration multiwell plates, specific immunoglobulin-enzyme conjugate and other required reagents. In a clinical trial performed on sera from 1,035 clinically suspected toxoplasmosis cases, the Sabin Feldman Dye Test (SFDT) and this ELISA system agreed closely. Relative to the SFDT, the sensitivity and specificity of the latter was 98.0% and 97.6% respectively with a correlation coefficient of 0.97. In a further study of 121 sera, the Indirect Fluorescent Antibody Test (IFAT), the Indirect Haemagglutination Test (IHAT) and this ELISA procedure showed over 90% agreement, with correlation coefficient of 0.98 and 0.95 respectively. Within the working concentration of specific antibody to T. gondii in human serum, there was a linear relationship between the ELISA values and the WHO international standard for human anti-Toxoplasma serum.

An evaluation of the ToxHA test for the detection of antibodies to Toxoplasma gondii in human serum

The titre of antibodies to Toxoplasma gondii was compared in 1985 sera by use of an indirect haemagglutination test (ToxHA test--Wellcome Reagents Ltd) and the dye test. Sera from 42 patients with clinical or serological indications of recent toxoplasmosis were also examined to determine if the ToxHA test would be of value in detecting early stages of the disease. Nine recent cases of lymphadenopathy and four cases of eye infection were not detected by the test. In addition, a large number of sera found negative in the dye test gave a positive result in the haemagglutination test.

Cerebral blindness and oculomotor nerve palsies in toxoplasmosis

We studied the clinicopathologic and neuro-ophthalmic manifestations of central nervous system toxoplasmosis in two patients who were being treated with immunosuppressive chemotherapy, one for renal transplantation and the other for systemic lupus erythematosis. Both pateints had oculomotor nerve palsies and later developed visual loss from cerebral involvement. Multifocal central nervous system toxoplasmosis appeared as a complication of their systemic diseases.

Age-sex distribution of Toxoplasma antibody in the South Australian population

Sera from 1071 patients in nine age categories were screened for Toxoplasma antibody by indirect immunofluorescence. Thirty per cent of the sera contained antibody at a titre greater than or equal to 1/16. The percentage of sera containing antibody rose from 3% in the 6 months--5 years age group to a maximum of about 40% in the 31--40 years age group. It remained constant thereafter. Eleven per cent of the 84 sera with Toxoplasma antibody titres greater than or equal to 1/128 had Toxoplasma IgM titres greater than or equal to 1/32. No significant difference was found in the possession of antibody between the sexes.

Epidemiology of toxoplasmosis in Kuwait. I. Detection of antibodies to Toxoplasma gondii and percentage distribution among the inhabitants

Of 246 people living in Kuwait and selected at random, 95.5% gave a positive reaction to the indirect haemagglutination test for antibodies to Toxoplasma gondii, of whom approximately 34% had medium to high titres (1:128 to 1:4096). There was no obvious difference between the proportion of females and males who had been infected. Approximately double the proportion of people in the age groups 20 to 31 and 32 to 43 years had medium to high titres compared with those in other age groups. Even between the former two groups, the percentage with the highest titres (1:512 to 1:4096) declined with age; none was found in the oldest group. When analysed in terms of nationalities, the pattern of results obtained with a small group of Bedouins, where most had medium to high titres, was the opposite of that found with urban Kuwaitis and people of other nationalities. It is suggested that the Bedouins may be particularly prone to the infection.

Comparison of immunofluorescence and radioimmunoassay for detecting IgM antibody in infants with the congenital rubella syndrome

Immunofluorescence (IF) and radioimmunoassay (RIA) have been compared as methods for detecting IgM antibody in 124 infants with confirmed or suspected congenital rubella. IF was used to test sucrose density gradient fractions and RIA to test fractions and whole serum. When fractions were tested IF and RIA were equally specific and distinguished clearly between IgM and IgG, but RIA was the more sensitive method. The RIA titre in whole serum was always greater than in the peak IgM fraction and there was no evidence that testing the serum, rather than the fraction, could result in failure to detect IgM. With some sera RIA gave low titres which became negative after absorption with IgG-coated latex beads. The mechanism of this 'false positive' effect, which may have been due to IgM with anti-IgG activity, was not investigated, but if it can be removed by absorption it need not reduce the specificity of the test. During the first 6 months of life IgM antibody was detected by RIA in 30 out of 32 unfractionated sera and by IF in fractions from 28 of these. After the age of 6 months IgM was found progressively less frequently and the greater sensitivity of RIA became a more obvious advantage: 17 out of 60 specimens were positive by RIA and 11 of these were negative by IF. RIA testing of whole serum appears to be an economical, specific and sensitive method for detecting IgM antibody in congenital rubella, of particular value when the titre of antibody is low.

Toxoplasmic infection in cardiac disease

In 18 patients who presented in less than 2 years with heart disease characterized by arrhythmias (including atrial fibrillation, ventricular arrhythmias and heart block), atypical chest pain, pericarditis and cardiac failure, extensive investigation revealed no cause for the disease except for evidence of toxoplasmic infection. One patient had acute toxoplasmosis; the other 17 patients had chronically increased titers, higher than the expected level in the community and also higher than in a control series of patients with well defined heart disease. Toxoplasmosis is probably a fairly common cause of heart disease in this community. The source of infection appeared to be cats, uncooked meat and congenital infection. Patients received chemotherapy with either pyrimethamine and sulfadiazine or tetracycline. Serious relapse occurrred in three patients and embolic complications in two. Experimental myocarditis occurs when toxoplasmic cysts rupture within the heart; therefore clinical symptoms may occur sporadically during a chronic infection.

Immunoglobulin G and immunoglobulin M enzyme-linked immunosorbent assays and defined toxoplasmosis serological patterns

Enzyme-linked immunosorbent assay (ELISA) for toxoplasmosis was evaluated in serum samples presenting defined toxoplasmosis serological patterns, as determined by results in immunoglobulin (Ig)G and IgM immunofluorescence (IgG-IF, IgM-IF), hemagglutination, and complement fixation tests. ELISA was carried out with alkaline phosphatase-labeled anti-IgG and anti-IgM antibodies. Serum titer was expressed as the serum dilution end point determined by mere observation of color development in the test. A straight agreement was found between IgG-ELISA and IgG-IF titers, both in group A sera of ancient infections (patterns II and III) and group B sera of recent infections (pattern I). A similar agreement was found between IgG-ELISA and hemagglutination titers in group A sera, for which coincident IgG-IF and hemagglutination titers are also frequent. However, in group B sera, in spite of the same toxoplasma extract being used to sensitize both plastic surfaces and erythrocytes, IgG-ELISA titers were much higher than hemagglutination titers, in a way similar to that observed for IgG-IF titers. IgM-ELISA was positive in every group B serum, with higher titers than corresponding IgM-IF titers. Occasional low-titered positive IgM-ELISA results were seen for group A sera, sometimes due to IgM-antiglobulin antibodies. An easy test to perform, ELISA seems to be an adequate substitute for toxoplasmosis IF tests for routine purposes.

Acquired toxoplasmosis in children

Nine cases of acquired toxoplasmosis, 8 from rural backgrounds, are described, illustrating the wide variety of clinical pictures. Evidence of familial infection was found whenever sought, and was also found in cattle in one case. The availability of an easily performed screening test should make diagnosis of this common disease more frequent.

Premarket evaluation of commercial toxoplasmosis indirect fluorescent-antibody reagents

The quality of commercial toxoplasmosis indirect fluorescent-antibody reagents was evaluated over a 6-year period. Seven manufacturers voluntarily submitted their products for evaluation in the Center for Disease Control Premarket Evaluation Program. Each product was tested in accordance with the Center for Disease Control performance and labeling specifications and evaluation methods. Only 49% of all of the products tested met the Center for Disease Control requirements. Performance criteria are outlined, and suggestions are offered to assist laboratorians in obtaining toxoplasmosis indirect fluorescent-antibody reagents of high quality.

Toxoplasmosis in Greater Victoria

Titres of antibody to Toxoplasma gondii were determined in 596 inhabitants of Greater Victoria who were either patients at two hospitals or healthy volunteers. The survey included 404 women of childbearing age, 305 of whom had just given birth. The proportion of persons with antibody to T. gondii at a titre of 1:8 or greater as determined by a methylene blue dye test was 28%. Titration of IgM antibody specific to T. gondii by the indirect fluorescent antibody test, performed in the serum samples with a titre of 1:8 or greater by the dye test, indicated that 3% of the 596 patients had recently acquired infection with T. gondii. The proportion of women with antibody to T. gondii among those who had just given birth was 25%, but the proportion among women aged 31 to 35 years who had just given birth was 37%.

Chronic lymphoglandular enlargement and toxoplasmosis in children

Serum antitoxoplasma titres were determined simultaneously by the direct agglutination and the indirect immunofluorescent tests in 52 children aged 2 to 16 years having chronic lymph node enlargement, mainly cervical. Direct agglutination titres were raised (64 to 4096) in 22 children (42%), but rarely in the control groups of children with acute suppurative lymphadenitis, and healthy children, adults, nurses, and physicians. It is concluded that toxoplasmosis is commoner in Greek children than previously believed, and that it should be included in the differential diagnosis of lymphoglandular enlargement. Clinically the condition is mild and may be self-limited, but it should be treated promptly with trimethoprim-sulphamethoxazole, in order to prevent reactivation in adult life.

Template method for the fluorescent-antibody technique

An easily constructed and inexpensive template has been developed, which enables the fluorescent-antibody technique to be applied to serial dilutions and allows 18 assays on a single microscope slide.

Radioimmunoassay for toxoplasmosis

A solid-phase radioimmunoassay for toxoplasmosis has been developed, and the results show good correlation with the indirect hemagglutination test.

A microplate enzyme-immunoassay for toxoplasma antibody

A new test for the detection and measurement of toxoplasma antibody is described. Test sera are reacted with antigen-sensitized wells in micro-haemagglutination plates. Any attached antibody is shown by the addition of an enzyme-labelled antiglobulin followed by assay of the enzyme reaction with its substrate. The test is easy to carry out on a large scale, and there is a positive correlation between the results and dye test and haemagglutination test titres.