A stable haemagglutinating antigen for detecting toxoplasma antibodies

Success in the toxoplasma dye test

OBJECTIVES

To compare the success rate of the toxoplasma dye test using different accessory factors (human serum as a source of complement) and different batches of tachyzoites produced in vivo and in vitro.

METHODS

Twenty-five accessory factors were used in the dye test to assess both types of tachyzoite. Batches of tachyzoites were produced in vivo (n = 49) and in vitro (n = 23) and their performance assessed against panels of accessory factors. Performance was recorded as success or failure (incorrect results, total killing or no killing).

RESULTS

With in vivo tachyzoites 21/25 accessory factors were successful in P > or = 1 dye test runs, whereas with in vitro tachyzoites all 25 were successful. One or more failure was recorded for 19/25 and 12/25 accessory factors using in vivo and in vitro tachyzoites, respectively (P < 0.05). The number of successful dye test runs was less for in vivo (92/141, 65%) than in vitro (140/163, 86%) tachyzoites (P < 0.001). This was due to a higher success rate in citrated accessory factors used for in vitro tachyzoites compared to the corresponding uncitrated accessory factors used for in vivo tachyzoites (P < 0.001). Success in the dye test was recorded for 48/49 and 23/23 batches of in vivo and in vitro tachyzoites, respectively. The number of successful dye test runs was lower with in vivo (156/234, 67%) than in vitro (116/142, 82%) tachyzoites (P < 0.01).

CONCLUSIONS

Success in the dye test may be due to the accessory factor, tachyzoites, or a combination of both. Problems due to the accessory factor can be minimized by careful quality control or use of modification procedures. Tachyzoites produced in vitro may also increase success in the dye test. Careful selection of accessory factor/tachyzoite combination makes it possible to use the dye test in a district general hospital.

Zoonotic infections in Northern Ireland farmers

Evidence of past zoonotic infection was investigated serologically in randomly selected Northern Ireland farmers. The percentage of farmers with antibody was: Brucella abortus (0.7), Leptospira interrogans serovars (8.1), Borrelia burgdorferi (14.3), Toxoplasma gondii (73.5), Coxiella burnetii (28.0), Chlamydia psittaci (11.1) and Hantavirus (1.2). The results show that Northern Ireland farmers have been exposed in the past to zoonotic infections. It is not known if these infections contributed to ill health in farmers but it is now time for the health of farm workers and their medical services to be reassessed.

Simultaneous diagnosis of toxoplasmosis in goats and goatowner's family

Four out of 6 goats from a small British goat herd gave birth to weak or stillborn kids. All were seropositive for Toxoplasma gondii. The parasite was isolated from the tissues of one kid and the milk of one goat. Concurrently, one of the goatowner's sons developed a mononucleosis-like illness with serological evidence of current toxoplasma infection. Investigation of the family showed past infection in the other son, but both parents were seronegative. The source of infection for both boys appeared to be the consumption of unpasteurized goat's milk.

Diagnosis of congenital toxoplasmosis in Scotland

During a period of 10 years (1976-1986) 853 cases of toxoplasmosis were identified serologically in the Toxoplasma Reference Laboratory in Scotland. Suspected cases of infection in pregnancy (29 cases) and of congenital infection (27 cases) were rare but ophthalmic disease was common (224 cases). In two of the congenital cases, maternal infection was identified during pregnancy. The other 25 babies were investigated because of suspected congenital infection. Toxoplasmosis was confirmed retrospectively in 11/25 babies and excluded in two of them. The other 12 cases remain unclassified. Diagnosis of infection in babies was difficult although the introduction of an IgM capture ELISA was of some help. IgM was detected by ELISA in 3/13 congenitally infected babies but by immunofluorescence tests in only one of these. In two antenatal studies, involving 16,000 women, an additional 32 women were identified whose babies might have benefited from treatment or the availability of fetoscopy for early detection of congenital infection.

Incidence of Toxoplasma infection in a population of European starlings Sturnus vulgaris from central England

A sample of European starlings, Sturnus vulgaris, culled from a communal roost in a city in Central England, was examined for infection with Toxoplasma. Eleven (8%) of 133 birds were confirmed as infected after horizontal passage of brain homogenate through mice. Serological examination, using the indirect and direct agglutination tests, proved unsatisfactory for screening starlings for Toxoplasma infection. If the proportion of starlings infected with Toxoplasma in this sample is representative of the population as a whole, then this bird could play an important role in the maintenance of the infection in urban environments.

Detection of toxoplasma IgM antibody by passive latex agglutination reaction

Three major components (designated Sp-1, -2 and -3) of the microsomal pellet of Toxoplasma gondii (Tp) were isolated by Ultragel AcA 44 gel filtration chromatography from the microsomal pellet solubilized with detergents. Of these, Sp-2 proved to be most reactive with anti-Tp antibodies and its reactivity with IgM and IgG antibodies varied with the concentration at which it was used for sensitizing latex particles. Sp-2 antigen reacted with IgM antibody alone when latex particles were sensitized with less than or equal to 100 micrograms of this antigen/mg of particles, and its reactivity with IgG antibody appeared and increased progressively with increasing sensitizing concentrations of this antigen. Based on this finding, a method of direct measurement of anti-Tp IgM antibody in serum by passive latex agglutination has been developed. Polyacrylamide disc gel electrophoretic analysis of Sp-2 antigen in the presence of SDS revealed four constituents of 43, 35, 28 and 14 kDa. All these components reached with both IgM and IgG when tested by immunoblotting.

Experimental infection of pregnant sheep with Toxoplasma gondii: pathological and immunological observations on the placenta and foetus

The pathogenesis of Toxoplasma gondii infection in pregnant sheep was investigated. In one experiment, sheep were infected at 40, 60 and 90 days gestation and examined 30 days later, while in a second experiment, pregnant sheep were infected at either 60 or 90 days gestation and examined 10, 15 and 20 days later. By 10 days post infection (dpi), the parasite had invaded the gravid uterus and caused focal damage in the caruncular septa and, by 15 days, the degenerative changes had spread to the crypt wall and trophoblast. At this time, toxoplasma were isolated from all challenged foetuses. Foetuses did not produce any significant immune response until 20 dpi when increased numbers of IgM positive cells were found in lymphoid tissues. However, at 30 dpi, the numbers were normal while numbers of IgG positive cells and circulating IgG were increased. It was concluded that, while the foetal immune system need not be fully mature to respond to T. gondii infection, its ability to mount a response is limited at 70 days gestation but becomes increasingly competent after this. Furthermore, while it is able to respond more comprehensively with increasing maturity, maturation itself appears to be accelerated by the stimulus of infection.

Prospective serological and clinical studies on infants born in Kuwait with an elevated IgM in cord blood

Little is known about congenital viral and toxoplasmal infections in the developing countries. This study attempts to provide preliminary data on such infections among Arab mothers and infants in Kuwait. Babies born with an elevated IgM in cord blood were selected at birth and then studied prospectively during the first year of life for serological and clinical evidence of viral and toxoplasmal infections. There appeared to be a significant association between the elevation of total cord blood IgM and the selection of cases with cytomegalovirus infection. Demonstration of specific IgM in cord sera was attempted, whenever possible, to provide further evidence of congenital infection and to exclude early postnatal infections. In 18.5% of cases there was an association between serological evidence of infection and certain clinical abnormalities. Apart from cytomegalovirus and rubella virus, no evidence was found for congenital infection by other viruses or toxoplasma in this study.

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.

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.

Toxoplasmosis in Northern Ireland 1982-83

During 1982-83, 1161 sera were examined for the presence of haemagglutinating antibodies against Toxoplasma gondii. The Indirect Haemagglutination Test (IHAT) was positive in 416 (35.8%). Fourteen patients were judged to be suffering from acute acquired toxoplasmosis (active disease). In addition, 11 patients were also found to have glandular fever.

Hydatid disease in the Western Isles

An investigation into the incidence of hydatid disease was carried out in the Hebridean islands of Lewis and Skye. The results showed that 20% of the sheep were infected and 10% of the dogs harboured Echinococcus granulosus. Sporadic human cases continue to occur but using serological tests we were unable to show evidence of subclinical infection in the population sampled.

Serological and parasitological survey of blood donors in Kenya for toxoplasmosis

322 samples of sera from blood donors in four areas of Kenya were screened for Toxoplasma gondii antibodies by haemagglutination and 54% proved positive. 299 of these were also tested by dye test and 42% were positive, with 5.9% showing high titres indicating possible active infection. Parasitological examination of the buffy coat from donors was also carried out on 100 samples but no Toxoplasma parasites were seen in spite of high antibody incidence. There appears to be little or no clinical toxoplasmosis in Kenya but serological studies indicate a widespread distribution of the parasite in the human population.

Comparative study of three tests (dye test, indirect haemagglutination test, latex agglutination test) for the detection of antibodies to Toxoplasma gondii in human sera

An evaluation has been made of a commercial latex agglutination test, Toxotest-MT (TMT) (Eiken, Japan), for the detection of antibodies to Toxoplasma gondii in human sera. In qualitative studies, 878 sera were examined in both the TMT and dye test (DT) and 96.6% agreement was found, In quantitative studies 339 sera were titrated in the TMT and DT, with 337 of these sera also titrated in the indirect haemagglutination test (IHAT). Agreement between the DT and TMT was best, 78% of the sera showing titres within +/- 1 dilution in the two tests. The IHAT and TMT gave 66% agreement, while the DT and IHAT showed least agreement, 40.9%. The results suggest that the pattern of antigenic determinants to which antibody levels are measured are different in the three test systems. The TMT is a better substitute for the DT than the IHAT.

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.

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.

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.

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

Three types of antibody curve have been demonstrated by testing sera during the course of acquired toxoplasmosis by six different techniques. These three types are due to cell-wall antibody, (demonstrated by four of the techniques), to antibody to soluble antigen, and to IgM antibody to the cell wall. These findings have been supported by absorption experiments. A scheme is presented for testing single sera by two or three different tests to indicate the stage and duration of the infection.