Molecular diagnosis of toxoplasmosis: recent advances and a look to the future

INTRODUCTION

Toxoplasmosis is a globally distributed parasitic infection that can be particularly severe when opportunistic or congenital. Its diagnosis requires accurate and rapid techniques that rely mainly on serology and molecular methods.

AREAS COVERED

The aim of this review was to discuss the positioning of the molecular diagnosis of toxoplasmosis according to the different clinical situations possibly resulting from infection with T. gondii, and to detail recent developments in this technique. The English and French literature were searched with the following keywords: 'Toxoplasmosis', "Molecular diagnosis" and 'PCR'.

EXPERT OPINION

Molecular techniques have revolutionized the diagnosis of toxoplasmosis, and practices have considerably evolved over the past decades. However, there is still a high degree of inter-laboratory heterogeneity which impairs comparisons between results and studies. Efforts to standardize practices are underway.

Toxoplasma gondii infection in Colombia with a review of hosts and their ecogeographic distribution

Toxoplasma gondii is one of the most prevalent zoonotic protozoan parasites among warm-blooded animal populations (humans included) around the world, causing multiple clinic manifestations including death in the most severe cases of infection. Due to the versatile life cycle of T. gondii and its diversity of potential hosts, there is a common perception that natural areas and wildlife are highly prevalent reservoirs for the parasite; however, information and reports of the parasite on wildlife populations in Colombia are scarce. Using PRC-based detection analyses of the B1 gene, we evaluated the presence of T. gondii in 49 native small mammal species (10% of the mammal species of Colombia) from 4 different undisturbed natural habitats. Additionally, to understand the ecogeographical distribution of the parasite in Colombia, we developed a literature search of infection reports including information on the host species, density of records and occurrence patterns (using landcover and ecoregions) in natural, rural and urban areas. Our literature review showed a total of 8,103 reports of T. gondii for Colombia of which 86% were related to humans, and 14% to non-human mammals and other categories, with just a single report associated to wildlife; additionally, 82% of all reports were associated to urban areas whereas only 18% to rural sites. Based on the negative results for the presence of T. gondii in our PCR-based analyses and our literature search, we suggest that T. gondii has a synanthropic distribution in Colombia occurring in ecoregions as variable as the xeric scrubs in the northern lowlands and humid montane Andean forests, also we show a lack of information on the parasite relationship with wildlife, a concerning fact given that zoonoses are the leading mechanism for the emergence of infectious diseases.

Influence of Two Major Toxoplasma Gondii Virulence Factors (ROP16 and ROP18) on the Immune Response of Peripheral Blood Mononuclear Cells to Human Toxoplasmosis Infection

Toxoplasma gondii ROP16 and ROP18 proteins have been identified as important virulence factors for this parasite. Here, we describe the effect of ROP16 and ROP18 proteins on peripheral blood mononuclear cells (PBMCs) from individuals with different clinical status of infection. We evaluated IFN-γ, IL-10, and IL-1β levels in supernatants from PBMCs cultures infected with tachyzoites of the T. gondii wild-type RH strain or with knock-out mutants of the rop16 and rop18 encoding genes (RHΔrop16 and RHΔrop18). Cytokine secretion was compared between PBMCs obtained from seronegative individuals (n = 10), with those with chronic asymptomatic (n = 8), or ocular infection (n = 12). We also evaluated if polymorphisms in the genes encoding for IFN-γ, IL-10, IL-1β, Toll-like receptor 9 (TLR9), and purinoreceptor P2RX7 influenced the production of the encoded proteins after ex vivo stimulation. In individuals with chronic asymptomatic infection, only a moderate effect on IL-10 levels was observed when PBMCs were infected with RHΔrop16, whereas a significant difference in the levels of inflammatory cytokines IFN-γ and IL-1β was observed in seronegative individuals, but this was also dependent on the host's cytokine gene polymorphisms. Infection with ROP16-deficient parasites had a significant effect on IFN-γ production in previously non-infected individuals, suggesting that ROP16 which is considered as a virulence factor plays a role during the primary infection in humans, but not in the secondary immune response.

Enzyme-Linked Aptamer Assay (ELAA) for Detection of Toxoplasma ROP18 Protein in Human Serum

Toxoplasma gondii engenders the common parasitic disease toxoplasmosis in almost all warm-blooded animals. Being a critical secretory protein, ROP18 is a major virulence factor of Toxoplasma. There are no reports about ROP18 detection in human serum samples with different clinical manifestations. New aptamers against ROP18 protein were developed through Systematic Evolution of Ligands by Exponential enrichment (SELEX). An Enzyme-Linked Aptamer Assay (ELAA) platform was developed using SELEX-derived aptamers, namely AP001 and AP002. The ELAA was used to evaluate total antigen from T. gondii RH strain (RH Ag) and recombinant protein of ROP18 (rROP18). The results showed that the ELAA presented higher affinity and specificity to RH Ag and rROP18, compared to negative controls. Detection limit of rROP18 protein in serum samples was measured by standard addition method, achieving a lower concentration of 1.56 μg/mL. Moreover, 62 seropositive samples with different clinical manifestations of toxoplasmosis and 20 seronegative samples were tested. A significant association between ELAA test positive for human serum samples and severe congenital toxoplasmosis was found (p = 0.006). Development and testing of aptamers-based assays opens a window for low-cost and rapid tests looking for biomarkers and improves our understanding about the role of ROP18 protein on the pathogenesis of human toxoplasmosis.

Seroprevalencia y detección molecular de Toxoplasma gondii en donantes de un banco de sangre de Cúcuta, Colombia

Introducción. La infección por Toxoplasma gondii puede presentarse en los humanos con un amplio rango de manifestaciones que van desde el estado asintomático hasta la enfermedad grave, según el estado inmunológico del individuo. Los mecanismos de transmisión incluyen la transfusión sanguínea, pero poco se sabe sobre la frecuencia del parásito en los bancos de sangre de Colombia.Objetivo. Determinar la prevalencia de la infección con T. gondii en donantes de un banco de sangre de Cúcuta mediante técnicas de diagnóstico serológico y molecular.Materiales y métodos. Se determinaron los anticuerpos IgG e IgM contra T. gondii mediante un inmunoensayo en suero en 348 donantes. Se determinó la frecuencia de ADN de T. gondii utilizando la reacción en cadena de la polimerasa (PCR) en sangre total de donantes seropositivos y se analizaron las variables de interés con base en la información obtenida durante la selección de donantes.Resultados. De los 348 donantes participantes, 134 (38,5 %) presentaron anticuerpos IgG contra T. gondii; dos (0,6 %) de ellos presentaron tanto IgG como IgM y, en dos (1,5 %), se detectó ADN del parásito en la sangre. Un análisis bivariado evidenció una asociación entre la seropositividad para T. gondii y tener más de 26 años de edad (p=0,020).Conclusiones. La prevalencia de la infección con T. gondii encontrada en los donantes de sangre sugiere una exposición significativa al agente, la cual adquiere relevancia al detectarse la parasitemia.

HIV-Related Cerebral Toxoplasmosis Revisited: Current Concepts and Controversies of an Old Disease

Cerebral toxoplasmosis is the most common cause of expansive brain lesions in people living with HIV/AIDS (PLWHA) and continues to cause high morbidity and mortality. The most frequent characteristics are focal subacute neurological deficits and ring-enhancing brain lesions in the basal ganglia, but the spectrum of clinical and neuroradiological manifestations is broad. Early initiation of antitoxoplasma therapy is an important feature of the diagnostic approach of expansive brain lesions in PLWHA. Pyrimethamine-based regimens and trimethoprim-sulfamethoxazole (TMP-SMX) seem to present similar efficacy, but TMP-SMX shows potential practical advantages. The immune reconstitution inflammatory syndrome is uncommon in cerebral toxoplasmosis, and we now have more effective, safe, and friendly combined antiretroviral therapy (cART) options. As a consequence of these 2 variables, the initiation of cART can be performed within 2 weeks after initiation of antitoxoplasma therapy. Herein, we will review historical and current concepts of epidemiology, diagnosis, and treatment of HIV-related cerebral toxoplasmosis.

Polymerase chain reaction (PCR) in ocular and ganglionar toxoplasmosis and the effect of therapeutics for prevention of ocular involvement in South American setting

INTRODUCTION

Cases of toxoplasmosis present in South America tend to be more severe than that found in other continents. Here, we present our clinical experience of ocular and ganglionar toxoplasmosis in the use of PCR, and of the treatment to prevent ocular involvement.

METHODOLOGY

Retrospective analysis of clinical charts of patients with ocular and lymphadenitic toxoplasmosis at the parasitology and tropical medicine consultation in the "Universidad del Quindio" in Colombia. In total, 91 records of cases with ocular toxoplasmosis and 17 with lymphadenitis that underwent PCR analysis for B1 repeated sequence in blood, were compared to the results of 104 people with chronic asymptomatic toxoplasmosis. In addition, 41 clinical records were included from patients with confirmed toxoplasmic lymphadenitis: 10 untreated, 6 that begun treatment after four months of symptoms, and 25 that were treated during the first four months of symptoms and had a follow-up during at least one year.

RESULTS

Patients with ocular toxoplasmosis or lymphadenitis had a higher probability of PCR positivity in peripheral blood than chronic asymptomatic people. There were no cases of retinochoroiditis in 25 patients with toxoplasmic lymphadenitis treated before 4 months of symptoms and followed during at least 12 months. In four out of ten untreated cases, new lesions of retinochoroiditis presented after the symptoms of lymphadenitis.

CONCLUSIONS

Toxoplasmosisin South America exhibits different clinical behavior and this influences the laboratory results as well as the need for treatment in the case of lymphadenitis. Clinicians should be aware of the geographical origin of the infection in order to adopt different therapeutic and diagnostic approaches.

Fatal disseminated toxoplasmosis in a zoological collection of meerkats (<i>Suricata suricatta</i>)

Two confirmed cases of fatal disseminated toxoplasmosis occurred in an urban zoological collection of meerkats (Suricata suricatta). Both cases are suspected to be the result of feral cats gaining access to the enclosure. Toxoplasmosis has rarely been documented in meerkats. Subsequent to prophylactic treatment of all the animals and structural changes being implemented within the enclosure, no new cases have been recorded to date. Very little information is available on the disease in viverrids.

Investigation of false positives associated with loop-mediated isothermal amplification assays for detection of Toxoplasma gondii in archived tissue samples of captive felids

Toxoplasma gondii is a ubiquitous protozoan parasite that infects humans and many different animals, including felids. Many molecular and serologic tests have been developed for detection of T. gondii in a wide range of hosts. Loop-mediated isothermal amplification (LAMP) is a field-friendly technique that lacks the practical drawbacks of other molecular and serologic tests, and LAMP assays have been successfully developed for detection of T. gondii in fresh tissue samples. In the current study, both a previously published and a de-novo designed LAMP assay were compared to a quantitative real-time (q)PCR assay, for the detection of T. gondii in archived formalin-fixed, paraffin-embedded (FFPE) tissue samples from captive wildlife. The LAMP assays produced conflicting results, generating both false positives and false negatives. Furthermore, the LAMP assays were unable to positively identify samples with low levels of parasites as determined by qPCR and histopathology. Therefore, these LAMP assays may not be the most suitable assays for detection of T. gondii in archived FFPE and frozen tissue samples.

Performance Testing of PCR Assay in Blood Samples for the Diagnosis of Toxoplasmic Encephalitis in AIDS Patients from the French Departments of America and Genetic Diversity of Toxoplasma gondii: A Prospective and Multicentric Study

BACKGROUND

Toxoplasmic encephalitis in patients with AIDS is a life-threatening disease mostly due to reactivation of Toxoplasma gondii cysts in the brain. The main objective of this study was to evaluate the performance of real-time PCR assay in peripheral blood samples for the diagnosis of toxoplasmic encephalitis in AIDS patients in the French West Indies and Guiana.

METHODOLOGY/PRINCIPAL FINDINGS

Adult patients with HIV and suspicion of toxoplasmic encephalitis with start of specific antitoxoplasmic therapy were included in this study during 40 months. The real-time PCR assay targeting the 529 bp repeat region of T. gondii was performed in two different centers for all blood samples. A Neighbor-Joining tree was reconstructed from microsatellite data to examine the relationships between strains from human cases of toxoplasmosis in South America and the Caribbean. A total of 44 cases were validated by a committee of experts, including 36 cases with toxoplasmic encephalitis. The specificity of the PCR assay in blood samples was 100% but the sensitivity was only 25% with moderate agreement between the two centers. Altered level of consciousness and being born in the French West Indies and Guiana were the only two variables that were associated with significantly decreased risk of false negative results with the PCR assay.

CONCLUSION/SIGNIFICANCE

Our results showed that PCR sensitivity in blood samples increased with severity of toxoplasmic encephalitis in AIDS patients. Geographic origin of patients was likely to influence PCR sensitivity but there was little evidence that it was caused by differences in T. gondii strains.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00803621.

Detection of Toxoplasma gondii in Diabetic Patients Using the Nested PCR Assay via RE and B1 Genes

BACKGROUND

Toxoplasma gondii is an obligate intracellular protozoan parasite that exists worldwide. Various techniques have been developed for T. gondii detection.

OBJECTIVES

The aim of this study was the detection of T. gondii in diabetic patients with RE and B1 genes and the comparison of these two genes for diagnosis using the nested-PCR assay method.

PATIENTS AND METHODS

DNA samples from 205 diabetic patients who had been referred to the diabetes center of Ali Asghar hospital in Zahedan, Iran, were collected and analyzed using the nested-PCR assay method. Toxoplasma antibody data gathered using the enzyme-linked immunosorbent assay (ELISA) method from a previous study was used to group patients. The data were analyzed using SPSS 18. The chi-square test was used for comparison.

RESULTS

Of the diabetic patients selected, the following results were obtained: 53 (IgG+, IgM+); 20 (IgG-, IgM+); 72 (IgG+, IgM-); and 60 (IgG-, IgM-). The nested-PCR detected the following: in the acute group, 21/53 (39.63%), 30/53 (56.60%) (IgM+, IgG+); in the chronic group, 40/72 (55.56%), 51/72 (70.83%), (IgG+, IgM-); in the false positive group, 18/20 (90%), 17/20 (85%) (IgM+, IgG-); and sero-negative samples of 38/60 (63.33%) and 60/ 41 (77.35%) for RE and B1 genes, respectively. The prevalence of toxoplasmosis showed positive in patients with diabetes in the B1 gene 139 (67.8%) and RE gene 117 (57.1%).

CONCLUSIONS

Our study demonstrated that the B1 gene, more so than the RE gene, showed positive samples and can be used to detect toxoplasmosis, although the B1 gene, in comparison to the RE gene, did not show any superiority of molecular diagnosing capability. Results also showed that toxoplasma molecular detection methods can be used instead of routine serological detection methods in a clinical laboratory testing.

A rational approach to select immunogenic peptides that induce IFN-γ response against Toxoplasma gondii in human leukocytes

The ideal vaccine to prevent toxoplasmosis in humans would comprise antigens that elicit a protective T cell type 1 response with high IFN-γ production. Here, we report the use of a bioinformatics pipeline to discover peptides based on biochemical characteristics that predict strong IFN-γ response by human leukocytes. We selected peptide sequences that previously were reported to induce IFN-γ to identify the biophysical characteristics that will predict HLA-A*02 high-affinity epitopes. We found that the protein motif pattern FL...L..[VL] was common in previously reported highly immunogenic sequences. We have selected new peptides with a length of 9 residues with affinities from 2 to 21 nM with peptide signal and transmembrane domains and predicted to be cleaved at the proteasome to perform ELISPOT assays with human leukocytes. Within 9 peptides with the highest scores for IFN-γ production, four peptides elicited IFN-γ levels in a range from 252 to 1763 SFC/1e6. Our pipeline uncovered Toxoplasma proteins with peptides that are processed by MHC class 1 in humans. Our results suggest that our rational strategy for the selection of immunogenic epitopes could be used to select peptides as candidates for inclusion in epitope-based vaccines.

Striking Divergence in Toxoplasma ROP16 Nucleotide Sequences From Human and Meat Samples

BACKGROUND

ROP16 is a protein kinase of Toxoplasma gondii identified in the mouse model as a virulent marker, but it is unknown whether this finding is relevant in human toxoplasmosis.

METHODS

We obtained the Toxoplasma ROP16 locus DNA sequence in samples from 12 patients with ocular toxoplasmosis, 1 sample from a patient with congenital toxoplasmosis, 22 samples from soldiers operating in the jungle, 2 samples from urban soldiers, and 10 samples from meat for human consumption. An enzyme-linked immunosorbent assay specific for antibodies against the ROP16 mouse-virulent peptide was performed in 46 serum specimens from patients with ocular toxoplasmosis and in 28 serum specimens from patients with chronic asymptomatic infection, of whom 19 had congenital infection and 11 had toxoplasmic lymphadenitis.

RESULTS

We found a striking divergence of the ROP16 nucleotide sequences. Ten of 12 sequences (83.3%) from patients with ocular toxoplasmosis clustered with those of mouse-virulent strains, whereas 7 of 7 ROP16 sequences (100%) from meat were clustered with those of mouse-avirulent strains. Only 11 of 104 serum specimens (10.5%) had specific antibodies against the mouse-virulent peptide, and there was no association between clinical forms and positive results of serological assays.

CONCLUSIONS

The majority of ROP16 nucleotide sequences from Colombian patients with ocular toxoplasmosis belonged to the group of mouse-virulent strains.

Toxoplasmosis in military personnel involved in jungle operations

Tropical diseases, mainly leishmaniasis and malaria, increased among Colombian military personnel due to intensive operations in the jungle in the last ten years; as a result the Colombian army developed important preventive strategies for malaria and leishmaniasis. However, no knowledge exists about toxoplasmosis, an emergent disease in military personnel. We compared the prevalence of IgG anti-Toxoplasma antibodies by ELISA and of parasitaemia by a real time PCR assay, in 500 professional soldiers that operated in the jungle with a group of 501 soldiers working in an urban zone (Bogotá). We found that the prevalence was significantly different between both groups of soldiers (80% in soldiers operating in jungle vs. 45% in urban soldiers, adjusted OR 11.4; CI 95%: 3.8-34; p<0.0001). All soldiers operating in the jungle drink unboiled and chlorine untreated lake or river water. In urban soldiers, these risk factors along with eating wild animal meat or eating tigrillo (little spotted cat) were significantly associated with a higher prevalence. Characteristic toxoplasmic choriorretinal lesions were found in 4 soldiers that operated in the jungle (0.8%) and in one urban soldier (0.19%). All soldiers before being deployed in jungle operations should be tested for Toxoplasma antibodies and to receive adequate health information about the routine use of personnel filters to purify their water for consumption.