A systematic review and meta-analysis of the validation of serological methods for detecting anti-Toxoplasma gondii antibodies in humans and animals

Toxoplasma gondii is a paradigmatic zoonotic parasite from the One Health perspective, since it is broadly distributed and virtually infects all warm-blooded species. A wide variety of serological techniques have been developed to detect T. gondii infection in humans and animals. Our aim was to describe and compare the main characteristics of these serological tests and validation processes and to critically analyze whether these tests meet the standards required to ensure an accurate serological diagnosis. The current systematic review and meta-analysis included 134 studies that were published from 2013 to 2023. QUADAS 2 tool was used to evaluate the quality of the included studies. A total of 52 variables related to the characteristics of the techniques and analytical and diagnostic validation parameters were studied. A wider panel of tests was developed for humans, including techniques exclusively developed for humans that involve costly equipment and the measurement of different Ig isotypes that are considered biomarkers of congenital toxoplasmosis. Studies conducted in humans frequently employed commercial techniques as reference tests, measured different immunoglobulin isotypes with a predominance for IgG (>50%) and discriminated between acute and chronic infections. In animals, the most commonly used reference techniques were in-house tests, which almost exclusively detected IgG. Common limitations identified in a large number of studies were some misunderstandings of the terms "gold standard" and "reference test" and the absence of information about the negative and positive control sera used or the exact cutoff employed, which were independent of the quality of the study. There is a lack of analytical validation, with few evaluations of cross-reactivity with other pathogens. Diagnostic odds ratio values showed that indirect ELISA based on native or chimeric antigens performed better than other tests. The reproducibility of serological test results in both humans and animals is not guaranteed due to a lack of relevant information and analytical validation. Thus, several key issues should be considered in the future, including interlaboratory ring trials.

A systematic review and meta-analysis of the serological diagnosis of Toxoplasma gondii infection highlight the lack of a One Health integrative research

Toxoplasma gondii is a globally distributed food-borne zoonotic parasite with numerous infection sources. The control of this zoonosis requires a One Health response that partially depends on serological monitoring in humans and animals. Herein, a systematic review and a meta-analysis were performed to analyse and compare the transdisciplinary and integrative research under the One Health approach. We searched for articles published between January 1st 2014 and September 5th 2022, focused on the development and evaluation of serological techniques for the diagnosis of T. gondii infection in humans and animals. After an exhaustive search on three scientific databases, a quality assessment was performed on 291 articles by QUADAS-2 tool, and 113 articles were finally selected. A total of 18 variables were extracted and analysed, including bibliometric characteristics, study aims and methodology. Remarkably, none of the studies included in the meta-analysis explicitly quoted the words "One Health", and only 23.9% of them alluded to the principles underlying the One Health approach; in particular, none were conducted by physician-only teams, with the majority of these studies involving interdisciplinary research teams, followed by veterinarians and by non-physician or non-veterinarian researchers. The One Health approach followed in the serodiagnosis of T. gondii still needs further integration among scientific disciplines, which is essential to design effective control strategies.

Detection of anti-Neospora caninum antibodies in sheep's full-cream milk by a time-resolved fluorescence immunoassay

Ovine neosporosis, caused by the Apicomplexan parasite Neospora caninum, leads to reproductive failure worldwide. Nowadays, there is a trend to develop diagnostic techniques using non-invasive samples, such as milk, in order to reduce animal stress, sample collection effort, and costs. The objective of this study was to develop and validate a highly sensitive and specific serological technique, based on a time resolved-fluorescence immunoassay using a N. caninum GRA7 antigen (GRA7-TRFIA), for the detection of anti-N. caninum immunoglobulins G on sheep' full-cream milk samples. An analytical validation was performed, including intra- and inter-assay precision, analytical sensitivity and accuracy. The diagnostic performance of the assay was evaluated by studying the positive-negative discrimination by Mann Whitney U tests. In additon optimal cut-offs, diagnostic sensitivity and specificity, and areas under the curve were calculated by three Receiver Operating Curve (ROC) analyses, using GRA7-TRFIA and a N. caninum tachyzoite soluble extract-based ELISA (NcSALUVET-ELISA) in blood sera, and the coinciding results of both techniques, as reference techniques. Moreover, Spearman's correlation of GRA7-TRFIA in milk with the techniques in sera and agreement (kappa values) were also estimated. GRA7-TRFIA for milk samples showed an adequate precision, with high analytical sensitivity and accuracy. Regarding ROC analyses, at the optimal cut-offs, the diagnostic sensitivity and specificity were more than 90 % in all cases. In addition, GRA7-TRFIA values in milk were more positively correlated to GRA7-TRFIA values in blood sera than in the case of values obtained with NcSALUVET-ELISA. GRA7-TRFIA in milk showed an almost perfect agreement with GRA7-TRFIA in blood sera (kappa = 0.98) and with the coinciding results of GRA7-TRFIA and NcSALUVET in blood sera (kappa = 1.00), while it has a substantial agreement with NcSALUVET-ELISA (kappa = 0.69). In the light of these results, GRA7-TRFIA in full-cream milk samples is a highly sensitive technique that could be used for screening anti-N. caninum antibodies in sheep flocks.

Changes in serum biomarkers of inflammation in bovine besnoitiosis

Background

Acute and chronic besnoitiosis in extensive natural-service herds can have relevant effects in the health of bulls and negative consequences in their productive performance. Recent progress has been made in order to elucidate the pathogenesis of this disease. In this context, the study of biomarkers of inflammation in serum would contribute to gaining knowledge about the physiopathology of bovine besnoitiosis. Serological biomarkers could help in early diagnosis and prognosis, as seropositive bulls may have mild or severe testicular lesions.

Methods

Herein, we have investigated the diagnostic and/or prognostic value of a panel of serum (serological) biomarkers related to inflammation, including total protein, globulin and albumin, haptoglobin (Hp), adenosine deaminase (ADA) paraoxonase-1 (PON-1) and acetylcholinesterase (AChE) in naturally and experimentally B. besnoiti-infected males classified according to different clinical phases of the disease (acute, chronic and subclinical besnoitiosis).

Results

Results showed a similar response pattern in these biomarkers for naturally and experimentally infected cattle, with a few relevant variations. Most significant changes occurred during the acute phase of infection, although significant changes in a few biomarkers were also observed during the chronic infection. Haptoglobin, albumin, PON-1 and ADA were identified as the biomarkers that showed changes of higher magnitude in the acute phase of the infection, whereas high total protein and globulin values were found in chronically infected cattle. We have described the changes of a panel of inflammatory biomarkers of acute and chronic bovine besnoitiosis.

Conclusions

In summary, several biomarkers with promising diagnostic value have been identified. The biomarkers associated with acute infection are related to previously reported molecular biomarkers in testicular parenchyma of infected bulls and could help in the diagnosis of early infections and complement results from specific immunoglobulin M (IgM) detection.

Graphical abstract

Seroprevalence of Toxoplasma gondii in outdoor dogs and cats in Bangkok, Thailand

The aim of this study was to estimate the seroprevalence and risk factors associated with Toxoplasma gondii exposure in dogs and cats from Bangkok, Thailand. Blood samples from 318 dogs and 321 cats were tested for T. gondii antibodies by modified agglutination test (cut-off 1:25). Additionally, 18 dogs and 20 cats were longitudinally sampled for T. gondii antibodies during the same study period, between June and July 2019. The overall seroprevalence in dogs and cats was 7.9% (25/318; 95% CI 4.9–10.8%) and 18.7% (95% CI 14.4–23.0%), respectively. For dogs, risk factors identified were being a mixed-breed animal and living totally outdoors, while increasing age was shown to be a risk factor for cats. Seroconversion was not detected and titres from positive animals remained constant over longitudinal study. The present study indicates that there is a prominent presence of T. gondii in urban and peri-urban areas of Bangkok, suggesting that outdoor dogs and cats should be considered as a possible risk factor for humans.

Development and validation of a time-resolved fluorescence immunoassay for the detection of anti-Toxoplasma gondii antibodies in goats

Toxoplasma gondii is a worldwide distributed parasite causing abortions and fetal malformations in small ruminants. The aim of this study was to design and validate a new immunoassay based on the use of TgSAG1-GRA8 chimeric antigen for the detection of anti-T. gondii antibodies in serum of goats. First, a time-resolved fluorescence immunoassay (TgSAG1-GRA8-TRFIA) was developed. In addition, the diagnostic performance of TgSAG1-GRA8-TRFIA was compared with an optimized enzyme-linked immunosorbent assay (TgSALUVET-ELISA) and a Western Blot (WB), both based on whole T. gondii tachyzoite antigenic extract. The TgSAG1-GRA8-TRFIA has shown a high intra- and inter-assay precision, analytical sensitivity and accuracy. The ROC analysis of this assay showed an optimal cut-off of 217.4 Units of Fluorometry for T. gondii (UFT), with 92 % of sensitivity and 90.48 % of specificity. A positive and statistically significant Spearman's correlation with TgSALUVET-ELISA was detected, and kappa value was 0.83, presenting high agreement with both methods. However, TgSAG1-GRA8 protein showed cross-reactivity with specific anti-Neospora caninum antibodies. Thus, TgSAG-1-GRA8 chimeric antigen seems not to be an ideal option for the serodiagnosis of T. gondii infection in goats unless combined with the serodiagnosis of N. caninum infection in parallel. In the light of the results obtained, a comprehensive study on the existence of cross-reactivities between T. gondii antigens used in serological tests employed in animal health and specific antibodies directed against Toxoplasmatinae parasites should be performed.