Discrepant toxoplasma latex agglutination test results

Serological Investigation of Bovine Toxoplasmosis Using Commercial and Indigenous ELISA Kits While Validating Cattle Toxo IgG ELISA Kit

Simple Summary

Toxoplasmosis is a zoonotic disease caused by T. gondii infection. The main aims of this study were to assess the seropositivity to toxoplasmosis of an exotic breed of cattle (n = 400) from different farms using the Latex Agglutination Test, validate the Cattle Toxo IgG ELISA kit with the help of the commercially available ELISA kit and compare the efficacy of the LAT and Cattle Toxo IgG ELISA kit for assessing seropositivity of cattle to toxoplasmosis. Four hundred cattle sera were collected from an exotic breed of cattle in Pakistan. These sera were evaluated through an LAT and Cattle Toxo IgG ELISA kit. Of 400 samples, 90 were elected and screened through a commercially available ELISA kit. The sensitivity and specificity of the Cattle Toxo IgG ELISA kit came out to be 100% and 96.15%, and in LAT, it was found as 26.31% and 61.53%, respectively. The Cattle Toxo IgG ELISA kit revealed 29.75% (119/400) seropositivity, 6% less than that found through LAT. The results of this study show that Cattle Toxo IgG ELISA kit is a highly accurate and reliable serodiagnostic tool to diagnose bovine toxoplasmosis.

Abstract

Toxoplasma gondii is a protozoan parasite that causes toxoplasmosis in warm-blooded vertebrates, globally. The main aims of this study were to assess the seropositivity to toxoplasmosis of an exotic breed of cattle (n = 400) from different farms using the Latex Agglutination Test and validate Cattle Toxo IgG ELISA kit. Of a total of 400 cattle sera that were evaluated by LAT, 143 (35.75%) were found positive. Based on these data, 90 samples (n = 60 seronegative by LAT; n = 30 seropositive by LAT) were elected for screening through a commercially available ELISA kit. The same 90 samples were screened through a Cattle Toxo IgG ELISA kit for validation purposes. Of 90 samples, 40 were seropositive in the Cattle Toxo IgG ELISA kit (100% sensitivity), and 38 were seropositive in a commercially available ELISA kit. All 50 samples in the Cattle Toxo IgG ELISA kit (96.15% specificity) were also seronegative in the commercially available ELISA kit. Hence, the sensitivity and specificity of the Cattle Toxo IgG ELISA kit came out to be 100% and 96.15%, and in LAT, it was found as 26.31% and 61.53%, respectively. Therefore, the Cattle Toxo IgG ELISA kit is a highly reliable serodiagnostic tool to diagnose bovine toxoplasmosis.

Toxoplasmosis after allogeneic haematopoietic cell transplantation-disease burden and approaches to diagnosis, prevention and management in adults and children

BACKGROUND

Toxoplasmosis is a rare but highly lethal opportunistic infection after allogeneic haematopoietic cell transplantation (HCT). Successful management depends on screening, early recognition and effective treatment.

OBJECTIVES

To review the current epidemiology and approaches to diagnosis, prevention and treatment of toxoplasmosis in adult and paediatric allogeneic HCT recipients.

SOURCE

Search of the English literature published in MEDLINE up to 30 June 2020 using combinations of broad search terms including toxoplasmosis, transplantation, diagnosis, epidemiology, prevention and treatment. Selection of articles for review and synthesis on the basis of perceived quality and relevance of content.

CONTENT

Toxoplasmosis continues to be a major challenge in the management of allogeneic HCT recipients. Here we provide a summary of published case series of toxoplasmosis in adult and paediatric patients post allogeneic HCT. We review and discuss the pathogenesis, epidemiology, clinical presentation, diagnosis and current recommendations for prevention and treatment. We also discuss impacts of toxoplasmosis in this setting and factors affecting outcome, emphasizing attention to neurological, neuropsychological and neurocognitive late effects in survivors.

IMPLICATIONS

Apart from careful adherence to established strategies of disease prevention through avoidance of primary infection, identification of seropositive patients and implementation of molecular monitoring, future perspectives to improve the control of toxoplasmosis in allogeneic HCT recipients may include the systematic investigation of pre-emptive treatment, development of immunomodulatory approaches, antimicrobial agents with activity against the cyst form and vaccines to prevent chronic infection.

Serological detection of T. gondii infection in humans using an immunochromatographic assay based on dense granule protein 7

Toxoplasma gondii causes toxoplasmosis, one of the world's most common parasitic diseases. It secretes large amounts of dense granule antigens (TgGRAs), which are crucial to the parasite's survivability. TgGRA7 is found abundantly on the surface of host cells, within the parasitophorous vacuole lumen and membrane, and the host cell cytosol. It stimulates a strong antibody response during acute and chronic infections. While it has been well utilized as an antigen for enzyme-linked immunosorbent assay (ELISA), only one report has documented its efficacy as an antigen for an immunochromatographic test (ICT) in pigs. To date, there is no study yet documenting its use for ICT in human toxoplasmosis. Here, we validated the efficacy of the TgGRA7-ICT we developed by testing 88 human sera. Results were compared with those obtained by ELISA based on TgGRA7, a commercial ELISA, and latex agglutination test (LAT). With high sensitivity, specificity, and kappa values, our TgGRA7-ICT results revealed very good agreement with standard test results. We also found a strong correlation between the relative ICT band intensity and absorbance values in the ELISA. Altogether, our data suggest that the current ICT with TgGRA7 is a reliable test for the diagnosis of human toxoplasmosis, which produced results similar to conventional serological methods. Thus, this can be used as a screening tool for routine testing of toxoplasmosis and a good option for point of care application. The present study also documents the first utilization of TgGRA7 as an antigen for ICT for the serodiagnosis of human toxoplasmosis.

Evaluation of Toxoplasma gondii propagated in specific pathogen free embryonated chicken egg, for diagnosis of toxoplasmosis in equids and human

Toxoplasma gondii (T. gondii) is a worldwide distribution infects a wide variety of mammals, including humans. The present study aimed to detect the efficacy of soluble and whole T. gondii antigens propagated in specific pathogen-free of embryonated chicken egg (SPF-ECE) used to improve the potency of serological assays for diagnosis of toxoplasmosis in equids and human. Total of 220 serum samples from 170 equids (90 donkeys and 55 horses and 25 mules) and 50 humans were collected from different governorates in Egypt during the period from October 2017 to March 2018. Crude T. gondii tachyzoites antigens from low or high passages propagated in mice or SPF-ECE was used for modifying some serological tests. The experiment showed that the mortality rate of T. gondii for 10³ and 10⁴ low passages were 6/8 (75%) and 7/8 (88%) dead embryos but, lower mortality rate in high passage T. gondii were 4/8 (50%) and 5/8 (63%) dead embryos, respectively. No mortality or inflammatory signs were observed in control of negative groups. In equids sera were examined by S-ELISA using soluble T. gondii antigen propagated in SPF-ECE showed the highest positive results 26 (28.8%), followed by LAT 37 (22%) and MAGPT 36 (21.17%). While, W-ELISA and IFAT used whole T. gondii antigen prepared in SPF-ECE were 35 (20.58%) and 28 (19.41%) showed highly positive results than the same test used the whole antigen prepared in mice. The highest seroprevalence of T. gondii in human and donkeys were 19/50 (38%). and 26/90 (28.88%), more than mules were 6/25 (24%) and horses were 9/55 (16.3%) examined by S-ELISA respectively. SPF-ECE is considered an appropriate experimental model for isolation and propagation of T. gondii tachyzoites, and their soluble antigens used in serological tests (S-ELISA, LAT, and MAGPT) have sensitivity and specificity more than the whole antigen and provided reliable diagnostic tools for detection of toxoplasmosis in human and equids.

Development and assessment of a latex agglutination test based on recombinant MSP5 to detect antibodies against Anaplasma marginale in cattle

The recombinant protein MSP5 has been established as an important antigen for serological diagnosis of Anaplasma marginale by enzyme-linked immunosorbent assay (ELISA). However, due to the high cost of specialized equipment, this technique is not accessible to all laboratories, especially in developing countries in areas where the disease is endemic. The present study describes the standardization of a latex agglutination test (LAT) to detect antibodies against A. marginale based on recombinant MSP5. Compared with indirect enzyme-linked immunosorbent assay (iELISA), the relative sensitivity and specificity of the LAT were 95.21% and 91.86% respectively, with an almost perfect agreement between tests (kappa index = 0.863). These results can be considered important for the serological diagnosis of A. marginale, as they indicate that the test represents a rapid and low cost alternative to ELISA.

A review on human toxoplasmosis

Toxoplasmosis is a worldwide infection caused by the intracellular parasite Toxoplasma gondii. At least a third of the world human population are infected with the parasite, making it one of the most successful parasitic infections. Primary maternal infection may cause health-threatening sequelae for the foetus, or even cause death in uterus. Reactivation of a latent infection in immune deficiency conditions such as AIDS and organ transplantation can cause fatal toxoplasmic encephalitis. Toxoplasmosis is a major cause of retinochoroiditis, especially in individuals with an impaired immune system. Despite the usually 'asymptomatic' nature of the infection, a significant burden imposed by the parasite necessitates the implementation of effective means for the prevention, diagnosis, and management of this disease. Laboratory diagnosis, i.e. PCR and serologic assays, plays the main role in the diagnosis of congenital infection and assists in the confirmatory diagnosis of toxoplasmic encephalitis and ocular toxoplasmosis. Here, we briefly review general aspects of Toxoplasma infection and focus on the diagnostic methods currently used in medical laboratories for the diagnosis of Toxoplasma infection.

Serological survey of Toxoplasma gondii and Campylobacter fetus fetus in sheep from New Zealand

AIM

To determine the prevalence of antibody titres to Toxoplasma gondii and Campylobacter fetus fetus in sheep from New Zealand.

METHODS

As part of a free screening service, unsolicited blood samples were supplied by veterinarians wishing to gauge the exposure of their clients' ewe flocks to T. gondii and C. fetus fetus. Blood samples were submitted from mixed-age ewes throughout New Zealand, from 2006 to 2009, that had not been vaccinated for T. gondii and C. fetus fetus. A total of 2,254 sera were serologically titrated for T. gondii and 3,429 for C. fetus fetus. A latex agglutination kit available commercially was used to quantify antibodies to T. gondii, and an agglutination test developed in-house was used for C. fetus fetus. For T. gondii, titres of ≥1:16 and ≥1:64 were used to define a positive response, and for C. fetus fetus a titre of ≥1:10 was defined as positive. A flock was defined as positive if ≥1 ewe had a positive titre.

RESULTS

Of the sera tested for T. gondii, 1,917/2,254 (85%) were positive, using a titre of ≥1:16, and 1,384/2,254 (61%) with a titre of ≥1:64. All 198 ewe flocks tested were seropositive to T. gondii, at a titre of ≥1:16, and all but three were at a titre of ≥1:64. A bimodal distribution was evident in the prevalence of titres to T. gondii suggesting that a percentage of titres ≤1:64 may have been non-specific. Of the sera tested for C. fetus fetus, 1,644/3,429 (48%) were positive to at least one of the four test antigens at titre of ≥1:10. Only 34/298 (11%) flocks tested for C. fetus fetus were completely seronegative. The percentage of seropositive ewes to both T. gondii and C. fetus fetus was significantly higher in the North Island than the South Island.

CONCLUSIONS

The study demonstrated that exposure to these two important infectious abortifacients was both considerable and widespread. Minimum titres were postulated to establish a 'cut-off' for a positive result and to allow comparison with past and future studies. The bimodal distribution evident for T. gondii suggested a titre of 1:64 may be an appropriate cut-off. The widespread on-farm exposure probably stimulates the immune response of vaccinated ewes.

CLINICAL RELEVANCE

Further studies are required to confirm the clinical significance of flock-based antibody responses, and to validate their use in identifying recently aborted ewes, especially where there are no aborted fetuses for examination.

Low incidence of primary infection with toxoplasma among women in Sheffield: a seroconversion study

OBJECTIVE

To determine the incidence of primary toxoplasma infection in women of childbearing age.

DESIGN

A retrospective study of seroconversion on stored pairs of sera taken for routine antenatal testing.

SETTING

The antenatal clinics and general practices of Sheffield between July 1989 and October 1992.

SUBJECTS

One thousand six hundred and twenty-one women on whom pairs of sera, separated by more than 500 days, had been received.

MAIN OUTCOME MEASURE

Rate of primary infection determined by seroconversion as measured by the presence of antibody in the second serum and its absence in the first.

RESULTS

Of 1621 women, 160 (9.9%) were initially seropositive. One seroconversion was detected in 2966 woman years of observation for susceptibles. The projected rate for primary infections was 0.23 (95% CI 0.0059-1.3) per 1000 pregnancies.

CONCLUSIONS

The rate is much lower than for earlier estimates of incidence in the UK but agrees with a more recent estimate from Sheffield and suggests a falling incidence.

Application of the polymerase chain reaction to the diagnosis of human toxoplasmosis

Toxoplasmosis may cause significant damage to the developing fetus and is a life-threatening opportunistic infection in immunocompromised persons. Serological investigation is unreliable, while isolation of the parasite is time consuming and may lack sensitivity. We have developed a system for detecting Toxoplasma gondii based on the amplification of the P30 gene using sequential rounds of PCR and nested primers. The clinical value of this technique was assessed by the investigation of a range of tissues taken from pregnant women, fetuses, neonates, AIDS patients and organ graft recipients. The PCR assay produced more positive reactions than isolation of the parasite by means of cell culture or animal inoculation. Extended autoradiography was found to be more sensitive than stained agarose gels for detecting the PCR product. Systematic contamination of PCR reactions was avoided but it was not possible to exclude sporadic contamination in certain cases. Detection of specific DNA is of clinical value in the investigation of the pregnant woman in order to assess the risk of transplacental passage of infection and in the fetus and neonate to identify congenital toxoplasmosis. Even so, PCR findings must be interpreted with caution because of the risk of a sample being contaminated. PCR may be the investigation of choice when brain biopsy is performed on a patient with AIDS and when toxoplasmosis associated with bone marrow transplantation is suspected.

Evaluation of five commercial assays for screening antenatal sera for antibodies to Toxoplasma gondii

AIMS

To evaluate the suitability of five commercial assays (Toxoreagent, DA, Captia Toxo IgG, Toxenz-G, Toxonostika-G) for screening large numbers of sera for antibodies to Toxoplasma gondii.

METHODS

Sera from 1000 pregnant women booking for antenatal care at a London hospital were screened in parallel by each test. Sera giving discordant results were retested.

RESULTS

The Captia Toxo IgG enzyme immune assay gave the best specificity on initial screening, with 0/773 false positives and only 2/218 false negatives. The Toxoreagent latex agglutination test performed well provided sera were tested at several dilutions to prevent prozone effects; 0/218 false negatives (greater than 12 IU/ml). Only one evidently false positive result was seen in the 1000 samples tested. The DA test gave no false negative results but produced 23/773 false positives. After repeat testing there were 9/1000 sera which gave equivocal results which were negative by the Captia Toxo IgG test (less than 12 IU/ml) but with low titres of 16 in the Toxoreagent test or 4 IU/ml in the DA test. In this situation women would have been asked for a follow up sample for repeat testing. Only 300 sera were tested by Toxenz-G; initial screening produced 4/58 false negative results and 4/242 false positives.

CONCLUSIONS

The Captia Toxo IgG test gave the fewest discordant results on initial screening. Results could be readily expressed in international units using a programmable plate reader, and this may be useful for epidemiological studies. The Toxoreagent test is considerably cheaper, and is a simple and reliable method for screening provided that at least two dilutions are used.

Laboratory techniques in the investigation of toxoplasmosis

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Incidence of toxoplasmosis in patients with glandular fever and in healthy blood donors

The differential diagnosis of the clinical syndrome of glandular fever may include Epstein-Barr virus, cytomegalovirus and Toxoplasma gondii infection. Some general practitioners and clinical laboratories choose to perform serological investigations for toxoplasmosis in all patients with glandular fever, who have negative Paul-Bunnell test results. The validity of this approach was assessed by a comparison of the incidence of toxoplasmosis in healthy blood donors and in a group of patients with clinically diagnosed glandular fever who had negative Paul-Bunnell tests. The results showed no significant difference in the frequency of acute or chronic toxoplasma infection between the two groups. In view of these findings, together with evidence of the lack of appropriate effective therapy for toxoplasmosis in immunocompetent individuals, and the dangers of failing to recognize concurrent severe disease of a separate aetiology, we recommend that Paul-Bunnell negative patients with clinically diagnosed glandular fever are not investigated for toxoplasmosis as a routine. However, these guidelines do not apply to patients at risk of severe sequelae from toxoplasma infection, notably pregnant women, who still require a full assessment.

New methods in the diagnosis and management of cerebral toxoplasmosis associated with the acquired immune deficiency syndrome

Cerebral toxoplasmosis is a life-threatening condition associated with the acquired immune deficiency syndrome (AIDS). Current diagnostic and therapeutic methods have serious limitations. The diagnosis of cerebral toxoplasma infection in a patient with AIDS was assisted by the detection of specific IgM in a highly sensitive immunosorbent agglutination assay and by the demonstration of Toxoplasma gondii nucleic acid in a brain biopsy specimen by means of the polymerase chain reaction. Following initial failure of the patient to respond to treatment with sulphadiazine and pyrimethamine, clinical improvement was observed during treatment with clindamycin followed by dapsone. Further assessment of novel methods in the management of cerebral toxoplasmosis is required.

Selective antenatal screening for toxoplasmosis and the latex agglutination test

Recent publicity concerning congenital toxoplasmosis has generated a demand for serological assessment of pregnant women. Many laboratories are requested to undertake primary screening in these cases. We assessed the latex agglutination test (LAT) findings in 158 specimens with detectable toxoplasma specific IgM derived from pregnant women. The LAT titres ranged from 16 to greater than or equal to 4000 reflecting the variable antibody response observed in acute toxoplasmosis. We recommend that non-reference laboratories test specimens from pregnant women using the LAT at a screening dilution of 1:16 and select all reactive samples for detailed investigation.

Serological study of the prevalence of toxoplasmosis in asymptomatic patients infected with human immunodeficiency virus

Asymptomatic individuals seropositive for antibody to human immunodeficiency virus (HIV) were investigated for the presence of toxoplasma specific antibody. Serological examination was performed using multiple assays. Of 500 patients studied 133 had serological evidence of previous exposure to Toxoplasma gondii. Specific IgM was detected in 7 patients using ISAGA and 2 patients by DS-ELISA. The immunoglobulin-G annual seroconversion rate was calculated to be 0.75%. The results of this study indicate 27% of HIV positive patients in the UK are at risk of developing life-threatening secondary reactivation of cerebral toxoplasmosis in association with AIDS. A further 0.5-1% per year may suffer primary toxoplasmosis.

False-negative dye-test findings in a case of fatal toxoplasmosis associated with cardiac transplantation

False-negative dye-test results were recorded in a case of fatal toxoplasmosis associated with cardiac transplantation. Serological and histological data require individual consideration in cases of suspected toxoplasma infection of the immunocompromised.

Assessment of immunoglobulin-M immunosorbent agglutination assay (ISAGA) for detecting toxoplasma specific IgM

An immunoglobulin-M immunosorbent agglutination assay (ISAGA) was introduced to detect toxoplasma specific IgM. This assay incorporates mu chain capture and use of entire toxoplasma trophozoites as an antigen source. The performance of the ISAGA was compared with that of a double sandwich enzyme linked immunosorbent assay (DS-ELISA) currently used in the Public Health Laboratory Service Toxoplasma Reference Laboratories. The ISAGA was found to be more sensitive than DS-ELISA but there was no demonstrable difference in the specificity or reproducibility between the two assays. The ISAGA is suitable for the diagnosis of acute toxoplasmosis in immunocompetent patients and as a screening test for recent infection in pregnant women. The persistence of ISAGA reactivity, however, is such that additional serological assessment is required to define the risk of congenital infection.

Direct agglutination test and other assays for measuring antibodies to Toxoplasma gondii

The performance of a direct agglutination test for the detection of toxoplasma specific IgG immunoglobulin was compared with that of the latex agglutination test. The direct agglutination test was less sensitive but more specific than the latex agglutination test. Quantitative results were not directly comparable, reflecting the different antibody profiles detected in each assay. The direct agglutination test represents an alternative to the latex agglutination test as a screening test for toxoplasmosis. Patients at risk of life threatening infection require detailed serological examination using additional assays.