• View in gallery

    Schematic representation of study design. GEB = guanidine–EDTA blood; IAC = internal amplification control; qPCR = quantitative polymerase chain reaction.

  • View in gallery

    Comparison of dynamic ranges between distinct blood specimens for qPCR detection for Toxoplasma gondii. Standard curves were built with Cq obtained from three replicates for each dilution of DNA isolated from clot, whole blood, and guanidine–EDTA blood. Both targets, B1 (A) and REP529 (B), were tested for each kind of sample.

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Development of a Novel Protocol Based on Blood Clot to Improve the Sensitivity of qPCR Detection of Toxoplasma gondii in Peripheral Blood Specimens

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  • 1 Laboratorio de Investigación en Enfermedades Infecciosas, Laboratorios de Investigación y Desarrollo, Universidad Peruana Cayetano Heredia, Lima, Peru;
  • 2 Department of Medicine, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina;
  • 3 Department of International Health, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland;
  • 4 Tulane University Medical Center, New Orleans, Louisiana;
  • 5 Hospital Regional de Loreto “Felipe Santiago Arriola Iglesias,” Iquitos, Peru;
  • 6 Infectious Diseases and Tropical Medicine Unit, Hospital Nacional Dos de Mayo, Lima, Peru;
  • 7 School of Animal and Comparative Biomedical Sciences, University of Arizona, Tucson, Arizona

Quantitative polymerase chain reaction (qPCR) for Toxoplasma gondii multicopy genes has emerged as a promising strategy for sensitive detection of parasite DNA. qPCR can be performed from blood samples, which are minimally invasive to collect. However, there is no consensus about what type of blood specimen yields the best sensitivity. The development of a novel protocol for qPCR detection of T. gondii using blood clot, involving an appropriate DNA extraction method and the use of an internal amplification control to monitor the reaction is presented in the current study. Assays directed to the B1 and REP529 genes were performed in spiked specimens of whole blood, guanidine–ethylenediaminetetraacetic acid blood, and clot. The clot-based qPCR was shown to be more sensitive when compared with other types of specimens, detecting five and 0.05 T. gondii genomes, using B1 and REP529 targets, respectively. Finally, a comparative analysis with samples from HIV patients with clinical suspicion of toxoplasmosis was performed, demonstrating the detection of four positive suspected cases with clots compared with only one using guanidine–ethylenediaminetetraacetic acid blood. The high analytical sensitivity and the cost-effective advantages offered by clot supports this methodology as a good laboratory tool to monitor parasite burden.

INTRODUCTION

Toxoplasmosis is a zoonotic disease caused by Toxoplasma gondii, an obligate intracellular coccidian parasite that infects humans and virtually all warm-blooded organisms, including birds, livestock, and wild mammals.1,2 The distribution of T. gondii is ubiquitous and the human interaction with this parasite is common; one-third of the human population is believed to be infected.3,4

In most cases toxoplasmosis is asymptomatic, however, it can cause serious and life-threading conditions in immunocompromised subjects.3,5 Toxoplasma encephalitis (TE) due to reactivation of latent toxoplasmosis in HIV patients is the most severe clinical manifestation seen in this group.68 In addition, the vertical transmission of this parasite is the most important among pathogenic protozoa in human pregnancy.9 This makes toxoplasmosis an important public health concern and the reliability of precise detection of T. gondii is crucial for opportune diagnosis and further treatment.

Traditional diagnosis of toxoplasmosis includes serological tests. However, this kind of approach has low sensitivity because of reactivation of the infection is not always followed by changes in antibody production, and correlation with neuroimaging is needed for accurate diagnosis.1012 For this reason, direct demonstration of the presence of parasite in tissues or body fluids would be a breakthrough for the diagnosis of this disease.

In recent decades, a wide arrange of DNA-based detection assays have been developed for T. gondii detection. Among these, amplification of parasite DNA by quantitative polymerase chain reaction (qPCR) was performed in different specimens, including amniotic fluid, tissue samples, cerebrospinal fluid, and blood.1316 Based on the premise that the sensitivity of qPCR is enhanced by the number of target sequences, the B1 gene (35 copies)17 and the 529-bp repeat element (REP 529, more than 300 copies)18 have been extensively used as targets for PCR detection.16,19,20 Nevertheless, collection of some specimens, such as brain tissue or cerebrospinal fluid, represent a risk and are not always easily obtained. In this way, blood offers many advantages as a low-invasive specimen and its usefulness in the diagnosis of toxoplasmosis by qPCR have been widely reported.16,21

Detection of T. gondii by qPCR is usually performed with DNA obtained from whole blood2224 and some studies recommend mixing the fresh specimen with guanidine or ethylenediaminetetraacetic acid (EDTA) to prolong the lifespan of the sample before DNA isolation.22 However, the shipping of this reagent is no longer allowed under the new International Air Transport regulations.25 This is a great obstacle for sample transportation and the development of efficient methods for DNA extraction and therefore efficient qPCR protocols from other blood specimens are needed.

Although there is no consensus about what kind of blood specimen is optimal for qPCR analysis, blood clot offers many cost-effective advantages for the collection and transport because this specimen does not require special containers for storage. In addition, the usefulness of the clot in qPCR has been previously reported in the diagnosis of Chagas disease and invasive aspergillosis, showing increased sensitivity when compared with serum or other blood specimens.25,26 However, clot has not been previously tested in the diagnosis of T. gondii and there is little information about the required parameters to maximize the recovery of parasite DNA from this specimen.

In this study, a practical method for appropriate DNA isolation from blood clot was developed for its use in qPCR directed to T. gondii genes B1 and REP529. An internal amplification control (IAC) was used to monitor the reaction. Spiked samples were used to confirm the increased sensitivity of the clot-based qPCR compared with whole blood in EDTA and guanidine–EDTA blood (GEB) specimens. In addition, this strategy was applied in a comparative quantitative analysis among blood samples of HIV patients with neurological symptoms and clinical suspicion of toxoplasmosis. In summary, the technical usefulness of blood clot as a cost-effective specimen to improve the sensitivity of qPCR aimed to monitor T. gondii burden was demonstrated.

Methodology.

Ethical statement.

Patient collection protocols were approved by the institutional review boards of the study hospitals and associated institutions: Hospital Regional de Loreto, Iquitos, Peru; Hospital Nacional Dos de Mayo, Lima, Peru; Asociación Benéfica Prisma, Lima, Peru; Universidad Peruana Cayetano Heredia, Lima, Peru; and University of North Carolina at Chapel Hill, Chapel Hill, NC. All patients, or their health care proxy, provided written informed consent for the collection of samples and subsequent analysis.

Cell culture for parasite stocks.

Monkey kidney fibroblast LLC-MK2 cells were cultured in Roswell Park Memorial Institute medium supplemented with 2% fetal bovine serum, ampicillin (1 μg/mL), and streptomycin (1 μg/mL) in a 25 cm2 blue vented-cap plastic flask incubated at 37°C in 5% CO2 and 95% humidity. Once the cell confluence was 70–80%, RH strain T. gondii tachyzoites were added (in a supplemented medium 100 mM sodium pyruvate, 15 g of L-glutamine and 500 g of essential amino acids) to the original cell culture. After 8–10 days, cultures were centrifuged and pellets were washed and resuspended in 1 mL of phosphate buffer saline 1×. Finally, the stock was diluted and counted in a Neubauer chamber until a desired load of 1 × 106 tachyzoites per mL was obtained.

Spiked blood specimen preparation.

Five healthy donors between the ages of 20 and 30 years, seronegative to toxoplasmosis, and with no significant previous medical history were recruited. Blood samples were collected in tubes with EDTA and tubes without additives. Blood with EDTA was preserved at −80°C as whole blood. Blood with additives was centrifuged at 1,000 g for 15 minutes, after which serum was drawn off to obtain the clot. For GEB, blood within EDTA tubes was mixed with guanidine in a proportion of 1:1. Each type of sample from healthy donors was aliquoted in volumes of 1 mL and spiked with 1 × 106 tachyzoites (Figure 1).

Figure 1.
Figure 1.

Schematic representation of study design. GEB = guanidine–EDTA blood; IAC = internal amplification control; qPCR = quantitative polymerase chain reaction.

Citation: The American Journal of Tropical Medicine and Hygiene 100, 1; 10.4269/ajtmh.17-0920

Study participants and clinical samples.

A total of 20 patients more than the age of 18, with ability to provide informed consent, who were previously diagnosed with HIV by two separate tests and with clinical suspicion of toxoplasmosis were recruited for this work. Ten individuals were recruited from Hospital Regional de Loreto, Iquitos, Peru (IQ-HIV), and 10 from Hospital Nacional Dos de Mayo, Lima, Peru (TOX-HIV). Participants from both locations were only included if their CD4+ cells count was lower than 250 cells/mL and if they had an onset of neurological symptoms within the last 6 months, or if they were examined by imaging and the diagnostic impression was associated with toxoplasmosis. This information was extracted from participants’ charts and the comments of the neuroimaging studies. Peripheral blood was collected from each patient and clot and GEB specimens were prepared for analysis following the methods described previously.

Internal amplification control.

To monitor the course of qPCR, a linearized plasmid containing a sequence of Arabidopsis thaliana (Table 1) was used as heterologous IAC.27 Both spiked and clinical specimens were co-extracted with 40 pg of IAC added immediately before the DNA extraction.

Table 1

Primer sets and probe sequences used for the detection of B1 and REP529 by quantitative polymerase chain reaction in this work

TargetProbe/primerSequence
B1ProbeFAM/BHQ 5′-CAA CAA CTG CTC TAG CG-3′
Forward5′-GCA TTG CCC GTC CAA ACT-3′
Reverse5′-AGA CTG TAC GGA ATG GAG ACG AA-3′
REP529ProbeFAM/MGB 5′-AGG AGA GAT ATC AGG ACT GTA-3′
Forward5′-GCT CCT CCA GCC CGT CCA AAC T-3′
Reverse5′-TCC TCA CCC TCG CCT TCA T-3′
ProbeVIC/MGB 5′-AGC ATC TGT TCT TGA AGG T-3′
Internal amplification controlForward5′-ACC GTC ATG GAA CAG CAC GTA-3′
Reverse5′-CTC CCG CAA ACC CTA TAA AT-3′

DNA extraction.

The specimens from both spiked and clinical samples were processed individually using High Pure PCR Template Preparation Kit (Roche Diagnostics Corp., Indianapolis, IN) following the manufacturer’s instructions. For clot specimens we completed a preceding homogenization step involving the addition of 300 μL guanidine hydrochloride 6 M (Sigma-Aldrich). After mixing, the sample was transferred to a Lysing Matrix H 2 mL tube (MP Biomedicals, Santa Ana, CA) followed by an agitation cycle in a FastPrep-24™ 5G machine (MP Biomedicals) (5.5 m/second–30″) to ensure the clot disaggregation before the treatment with proteinase K. The DNA from each kind of sample was eluted with 100 µL of kit’s elution buffer, quantified in NanoDrop™ (Thermo Fisher Scientific, Waltham, MA) and stored at −20°C. DNA obtained from spiked blood specimens was serially diluted 10-fold with healthy donor DNA solution to cover an expected range between 1 and 105 parasites for calibration curves.

Serial dilution assay.

To more effectively assess the limits of detection and analytical performance of qPCR assays, we calculated the parasite loads in terms of T. gondii genomes per PCR tube (Tgg) following the criteria described by Sterkers et al.28 We reported the percentage of positive reactions after testing the qPCR protocol in five replicates for every spiked blood specimen in equivalents of 5, 0.5, and 0.05 Tgg per reaction.

Quantitative polymerase chain reaction detection of B1 and REP529.

To perform a qPCR assay, fluorescence resonance energy transfer hybridization probes were used for genes B1 and REP529. Both the probes and primers sequences have been previously tested for T. gondii diagnosis29 (Table 1). A single qPCR included 10 μL Taqman® Universal PCR Master Mix II 1× (Roche), 1.2 μL of each primer (10 μM), 0.4 μL of probe (0.25 μM), 2.2 μL of MiliQ water, and 5 μL of DNA (20–150 ng/μL). In addition, 0.3 μL of IAC primers (5 μM) and 0.3 μL of probe (10 μM) were added. The amplification protocol involved two initial stages at 50°C and 95°C for 10 minutes each and 40 cycles at 95°C for 15 seconds followed by 60°C for 1 minute and was performed in a Light Cycler® (Applied Biosystems, Foster City, CA). The threshold cycle or cycle of quantification (Cq) obtained for each clinical sample was correlated with the calibration curve.

Statistical analysis.

The experiments were performed in triplicates. For standard curve analysis, data were expressed as arithmetic mean ±  standard deviation. Linear regression analysis was performed to test goodness of fit and Student’s t-test was used to analyze the statistical significance of the observed slopes. A P value of less than 0.05 was considered statistically significant. All the tests were calculated using Prism software (Graphpad®, San Diego, CA).

RESULTS

Comparison of analytical sensitivity of qPCR from blood specimens.

After the qPCR was performed, the quantification cycle (Cq) was obtained from the standard curves and the reportable range of B1 and REP529 between clot, whole blood, and GEB was compared. For this purpose, DNA isolated from spiked blood specimens were used to construct three independent standard curves ranging from 105 to 1 tachyzoites per mL. High linearity and adequate slopes were observed in curves from all samples, independent of the target. Calculated efficiency from all curves also showed high values (Table 2).

Table 2

Standard curve parameters from quantitative polymerase chain reaction assays performed for sample specimens

SpecimenTargetSlopesInterceptr2Amplification efficiency* (%)
ClotB1−3.44942.590.97594.95
REP529−3.40035.720.99496.84
Whole bloodB1−3.25939.330.994102.64
REP529−3.33229.560.9899.99
Guanidine–EDTA bloodB1−3.20543.120.98105.12
REP529−3.10537.890.99109.92

* Amplification efficiency was calculated based on the slope of the standard curve according to the minimum information for publication of quantitative real-time PCR experiments (MIQE) guidelines.34 In all the standard curves, the slope of the regression line is significantly different from zero (P < 0.0001).

The Cq values obtained from the clot standard curve detected the lowest parasite load when compared with the ones from whole blood and GEB. Each dilution was evaluated in triplicate and the standard deviation obtained was less than 1.3. Assays with B1 as target allowed for the detection of 10 parasites in clot as compared with 100 parasites in GEB and whole blood. By contrast, qPCR using REP529 detected one parasite in clot as compared with 10 parasites in whole blood and GEB. Thus, there is a 10-fold increase in sensitivity when using clot for either B1 or REP529 assays (Figure 2).

Figure 2.
Figure 2.

Comparison of dynamic ranges between distinct blood specimens for qPCR detection for Toxoplasma gondii. Standard curves were built with Cq obtained from three replicates for each dilution of DNA isolated from clot, whole blood, and guanidine–EDTA blood. Both targets, B1 (A) and REP529 (B), were tested for each kind of sample.

Citation: The American Journal of Tropical Medicine and Hygiene 100, 1; 10.4269/ajtmh.17-0920

However, the elution volume during DNA isolation might affect or overestimate the limits of detection of qPCR assay. To address this, we additionally performed a group of assays aimed to detect parasite load units in terms of 5, 0.5, and 0.05 Tgg. This choice allowed a straightforward comparison between specimens.

With B1 as the target, the clot-based qPCR detected 0.5 Tgg in 60% of replicates, whereas assays in GEB and whole blood could only detect 5 Tgg properly. Again, when REP529 is used as target, the qPCR performed in clot detected the lowest parasite load (0.05 Tgg) in all its replicates. By contrast, qPCR in whole blood (0.5 Tgg, 40% positives) and GEB (0.5 Tgg, 20% positives) showed a lower sensitivity and reliability (Table 3).

Table 3

Performances of qPCR for each blood specimen in terms of genomes of Toxoplasma gondii per qPCR

SpecimenTarget50 Tgg0.5 Tgg0.05 Tgg
Np/Total%PNp/Total%PNp/Total%P
ClotB15/5*3/560%0/50%
REP5295/5*5/5*5/5*
Guanidine–EDTA bloodB15/5*0/50%0/50%
REP5295/5*1/520%0/50%
Whole bloodB15/5*0/50%0/50%
REP5295/5*2/540%0/50%

qPCR = quantitative polymerase chain reaction; Tgg = T. gondii genomes. Quantitative polymerase chain reaction for each target was tested in five independent replicates to assess the number of positives from total (Np/Total) and the percentage of detection (%P). The parasite equivalents in Tgg were constructed considering 100 μL of elution volume during DNA extraction.

* 100% positive reactions.

Detection of T. gondii in HIV patients’ blood samples.

To validate the standardized protocols, blood specimens from 20 HIV patients were analyzed by qPCR. Considering the higher sensitivity yielded using REP529, experiments in clinical samples were performed only using this target. For each sample, only clot and GEB specimens were prepared simultaneously. Of the 20 patients, T. gondii was detected from clot specimens in four cases with the symptomatology of toxoplasmosis. By contrast, only one GEB sample was found to be positive (Table 4). These results reflect again, the high detection power of the clot samples over the other blood specimens. Whole blood was not analyzed because it was impossible to prepare immediately after collection.

Table 4

Quantitative polymerase chain reaction with blood samples from HIV patients with suspicion of toxoplasmosis using REP 529

Sample IDClinical impressionQuantitative polymerase chain reactionCq–clotCq–GEB
HIV patients
 IQ-004Neurological syndromes. CD4+ cells/mL: 73.NEGATIVE
 IQ-007Neurological syndromes. CD4+ cells/mL: 195.POSITIVE35.18 ± 0.21
 IQ-008Neurological syndromes.NEGATIVE
 IQ-009Neurological syndromes. CD4+ cells/mL: 30.NEGATIVE
 IQ-010Neurological syndromes. CD4+ cells/mL: 38.NEGATIVE
 IQ-012MRI: Inflammatory process related to infectious disease, toxoplasmosis. Neurological syndromes. CD4+ cells/mL: 45POSITIVE34.83 ± 0.18
 IQ-013CT: Multiple granulomas, brain strokes, and toxoplasmosis. Neurological syndromes. CD4+ cells/mL: 33.NEGATIVE
 IQ-014Neurological syndromes. CD4+ cells/mL: 44NEGATIVE
 IQ-015MRI: Brain strokes, toxoplasmosis. Neurological syndromes. CD4+ cells/mL: 182.NEGATIVE
 IQ-023MRI: Multiple granuloma, vasogenic cerebral oedema, and toxoplasmosis. Neurological syndromes. CD4+ cells/mL: 97.POSITIVE32.59 ± 0.3333.47 ± 0.51
 TOX-02Neurological syndromes. CD4+ cells/mL: 97.NEGATIVE
 TOX-03Neurological syndromes. CD4+ cells/mL: 153.NEGATIVE
 TOX-04MRI: Toxoplasmosis and progressive multifocal leukoencephalopathy. Neurological syndromes. CD4+ cells/mL: 13.NEGATIVE
 TOX-05Neurological syndromes. CD4+ cells/mL: 82NEGATIVE
 TOX-06Neurological syndromes.NEGATIVE
 TOX-07MRI: Multiple granuloma, cerebral oedema, and toxoplasmosis. Neurological syndromes. CD4+ cells/mL: 138.NEGATIVE
 TOX-08Neurological syndromes.NEGATIVE
 TOX-09MRI: Inflammatory process related to infectious disease and toxoplasmosis. Neurological syndromes. CD4+ cells/mL: 45NEGATIVE
 TOX-10MRI: Inflammatory process related to infectious disease, brain strokes, and toxoplasmosis. Neurological syndromes. CD4+ cells/mL: 35.POSITIVE31.15 ± 0.37
 TOX-11MRI: Brain strokes and toxoplasmosis. Neurological syndromes. CD4+ cells/mL: 51.NEGATIVE
Healthy donors
 H-01Not significant.NEGATIVE
 H-02Not significant.NEGATIVE
 H-03Not significant.NEGATIVE
 H-04Not significant.NEGATIVE
 H-05Not significant.NEGATIVE

Cq = cycle of quantification; MRI = magnetic resonance imaging; CT = computed tomography scan.

DISCUSSION

The diagnosis of TE by PCR has been previously tested for HIV patients in cerebrospinal fluid and using the B1 gene as the target, showing a sensitivity of 83%.30 However, lumbar puncture is an invasive procedure that could be contraindicated in some cases. Therefore, the design of new protocols based on less invasive biological specimen collection represents a great opportunity to improve the power of DNA-based approaches for the diagnosis of toxoplasmosis. In the present study, we aimed to design an efficient protocol to detect T. gondii in blood clot by qPCR. Thus, the efficiency of distinct sample specimens was assessed for its practical usefulness in diagnosis. Two sets of primers and probes, directed to B1 and REP529, were evaluated among the specimens.

After Cq analyses were performed, a better power of detection for all blood specimens was demonstrated when REP529 was used as the target (Table 5). The effect of copy number in qPCR sensitivity has been discussed previously, and indicates the usefulness of REP529 for the diagnosis of toxoplasmosis based on its high copy number and high level of conservation of nucleotide sequence between parasites isolates and strains.16,18 Moreover, the heterogeneity of B1 is well known and represents a great challenge for primer and probe design.31 This fact may largely affect the amplification power because some parasite strains may not share the nucleotide sequences.

Table 5

Mean Cq of 10-fold dilutions of Toxoplasma gondii tachyzoites on blood specimens for quantitative polymerase chain reaction assays

Tachyzoites/mLMean Cq ± standard deviation
ClotWhole bloodGuanidine–EDTA blood
B1REP529B1REP529B1REP529
10524.89 ± 1.12 (24.28–26.58)18.23 ± 0.54 (17.69–18.77)26.41 ± 0.31 (26.10–26.73)22.62 ± 0.04 (22.58–22.67)27.04 ± 0.29 (26.73–27.33)22.28 ± 0.21 (22.09–22.51
10428.55 ± 1.12 (27.88–30.23)21.74 ± 0.56 (21.30–22.38)28.87 ± 0.38 (29.48–30.25)26.38 ± 0.14 (26.22–26.50)30.25 ± 0.33 29.93–30.6025.53 ± 0.19 (25.30–25.66)
10331.94 ± 0.88 (31.24–33.23)25.52 ± 0.14 (25.38–25.66)33.51 ± 0.32 (33.21–33.86)28.97 ± 0.20 (28.73–29.09)33.74 ± 0.13 (33.66–33.90)28.65 ± 0.38 (28.42–29.09)
10235.54 ± 0.41 (35.15–36.11)28.84 ± 0.12 (28.69–28.92)36.49 ± 0.43 (36.17–36.98)31.95 ± 0.31 (31.72–32.17)36.56 ± 1.08 (35.64–37.76)31.66 ± 0.38 (31.23–31.98)
1039.22 ± 0.55* (38.83–39.61)32.56 ± 0.39 (32.11–32.82)NA35.77 ± 0.21* (35.62– 35.92)NA34.65†
1NA36.01 ± 1.29 (35.09–36.93)NANANANA

Cq = cycle of quantification; NA = no amplification.

* Two of three replicates detected.

† One of three replicates detected.

Although previous studies reported the low sensitivity of qPCR test based on blood for the diagnosis of TE,32 the appearance of false negatives might be a consequence of the low recovery of DNA in the sample, the presence of PCR inhibitors, or the effect of large quantities of human genomic DNA competing with the parasite DNA. Therefore, the design of an appropriate test should include protocols that account for DNA-associated difficulties due to the nature of blood specimens.

Our results indicated that clot specimens yield a better sensitivity for qPCR when compared with whole blood and GEB (Figure 2, Table 5). The usefulness of clot as a diagnostic specimen has been discussed for Chagas disease where it was found to have a higher sensitivity compared with buffy coat and whole blood.25 This phenomenon may be a consequence of parasite entrapment within the cellular portion of the clot or the sedimentation of circulating parasites. In addition, previous studies (H. Mayta, unpublished data) have shown that the sensitivity of qPCR is improved when the clot is treated with lysing matrices on a tissue homogenizer. These tools may allow a better lysis of the clotted blood and the trapped parasites, leading to a larger amount of DNA extraction. This observation is consistent with other reports for the diagnosis of invasive aspergillosis, where mechanical pretreatment of the clot increased DNA yield and improved the diagnostic sensitivity of the qPCR test.26

The diagnosis of toxoplasmosis is a difficult task and several studies have reported poor sensitivities in conventional PCR methods made from peripheral blood, probably as a consequence of low parasite loads.33 These observations are congruent with our results, where the Cq for positive samples reached high values that reflect very low parasite load (Table 4).

The protocol designed in our study highlights the power of detection by clot as a reliable specimen for the diagnosis of toxoplasma in immunocompromised patients. Finally, our results corroborate previous studies on qPCR-based diagnosis of toxoplasmosis, supporting the use of this design for an efficient detection of parasite burden in blood samples. The analysis based on clot provides several advantages as a cost-effective sample. Moreover, the high sensitivity of clot qPCR suggests the widespread use of this type of specimen as a powerful resource for T. gondii detection.

Acknowledgments:

We would like to acknowledge Rafael Saavedra Durán from the Instituto de Investigaciones Biomédicas (Mexico) and Ricardo Wagner de Almeida Vitor from the Federal University of Minas Gerais (Brazil) for their kind donations of the RH and ME49 strain tachyzoites, respectively.

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Author Notes

Address correspondence to Renzo Gutierrez-Loli, Laboratorio de Investigación en Enfermedades Infecciosas, Laboratorios de Investigación y Desarrollo, Universidad Peruana Cayetano Heredia, Av. Honorio Delgado 430, SMP 15102, Lima, Peru. E-mail: renzo.gutierrez@upch.pe

Financial support: This work was partially funded with the support of “Programa Nacional de Innovación para la Productividad y Competitividad” (Innóvate Perú), contract No. 137-PNICP-PIAP-2015. R. G. is supported by a training grant from NIH-Fogarty (2D43TW007120-11A1). Dr. Gilman’s NIH grant 1D43TW010074-01 supported the training of many of the Peruvian and Bolivian authors and working group members.

Prior presentation of findings: A poster titled “Real-time PCR strategy for detection of Toxoplasma gondii from peripheral blood clot” (Abstract Number: 3331-1882) was presented in November 2017 at the Annual Meeting of the American Society of Tropical Medicine and Hygiene in Baltimore, MD.

Authors’ addresses: Renzo Gutierrez-Loli, Cusi Ferradas, Andrea Diestra, Aliki Traianou, Holger Mayta, Maritza Calderon, and Jaeson S. Calla-Choque, Laboratorio de Investigación en Enfermedades Infecciosas, Laboratorios de Investigación y Desarrollo, Universidad Peruana Cayetano Heredia, Lima, Peru, E-mails: renzo.gutierrez@upch.pe, cusi.ferradas@upch.pe, andreadiestra13@gmail.com, aliki.traianou@gmail.com, holger.mayta@upch.pe, mmcalderons@yahoo.es, and jcalla@ucsd.edu. Natalie Bowman, Department of Medicine, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC, E-mail: natalie.bowman@gmail.com. Jeroen Bok, Hannah Steinberg, and Robert H. Gilman, Department of International Health, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD, E-mails: jeroenbok87@gmail.com, hannahsteinberg08@gmail.com, and gilmanbob@gmail.com. Melissa Reimer-McAtee, Tulane University Medical Center, New Orleans, LA, E-mail: mreimer2@tulane.edu. Cesar Ramal, Hospital Regional de Loreto “Felipe Santiago Arriola Iglesias,” Iquitos, Peru, E-mail: ramalasayag@yahoo.fr. Eduardo Ticona, Infectious Diseases and Tropical Medicine Unit, Hospital Nacional Dos de Mayo, Lima, Peru, E-mail: eticonacrg@gmail.com. Charles Sterling, School of Animal and Comparative Biomedical Sciences, University of Arizona, Tucson, AZ, E-mail: csterlin@email.arizona.edu.

Working Group: Linda Chanamé Pinedo, Gaston Valencia, Lenny Sanchez, Edith Málaga, Deanna Zhu, Juan Jiménez, Caryn Bern, Noelia Angulo, Francesca Schiaffino, Janet Acosta, Meredith Holtz, Daniel Clark, Taryn Clark, Grace Trompeter, Jeong Choi, Omar Gandarilla, Mauricio Dorn, Enzo Fortuny, Gerson Galdos, and Roni Colanzi.

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