Performance Evaluation of VIDAS® Diagnostic Assays Detecting Anti-Chikungunya Virus IgM and IgG Antibodies: An International Study

Chikungunya (CHIK) is a debilitating mosquito-borne disease with an epidemiology and early clinical symptoms similar to those of other arboviruses-triggered diseases such as dengue or Zika. Accurate and rapid diagnosis of CHIK virus (CHIKV) infection is therefore challenging. This international study evaluated the performance of the automated VIDAS^® anti-CHIKV IgM and IgG assays compared to that of manual competitor IgM and IgG ELISA for the detection of anti-CHIKV IgM and IgG antibodies in 660 patients with suspected CHIKV infection. Positive and negative agreements of the VIDAS^® CHIKV assays with ELISA ranged from 97.5% to 100.0%. The sensitivity of the VIDAS^® CHIKV assays evaluated in patients with a proven CHIKV infection confirmed reported kinetics of anti-CHIKV IgM and IgG response, with a positive detection of 88.2-100.0% for IgM ≥ 5 days post symptom onset and of 100.0% for IgG ≥ 11 days post symptom onset. Our study also demonstrated the superiority of ELISA and VIDAS^® assays over rapid diagnostic IgM/IgG tests. The analytical performance of VIDAS^® anti-CHIKV IgM and IgG assays was excellent, with a high precision (coefficients of variation ≤ 7.4%) and high specificity (cross-reactivity rate ≤ 2.9%). This study demonstrates the suitability of the automated VIDAS^® anti-CHIKV IgM and IgG assays to diagnose CHIKV infections and supports its applicability for epidemiological surveillance and differential diagnosis in regions endemic for CHIKV.

Assessment of serum total 25-hydroxyvitamin D assays for Vitamin D External Quality Assessment Scheme (DEQAS) materials distributed at ambient and frozen conditions

The Vitamin D External Quality Assessment Scheme (DEQAS) distributes human serum samples four times per year to over 1000 participants worldwide for the determination of total serum 25-hydroxyvitamin D [25(OH)D)]. These samples are stored at -40 °C prior to distribution and the participants are instructed to store the samples frozen at -20 °C or lower after receipt; however, the samples are shipped to participants at ambient conditions (i.e., no temperature control). To address the question of whether shipment at ambient conditions is sufficient for reliable performance of various 25(OH)D assays, the equivalence of DEQAS human serum samples shipped under frozen and ambient conditions was assessed. As part of a Vitamin D Standardization Program (VDSP) commutability study, two sets of the same nine DEQAS samples were shipped to participants at ambient temperature and frozen on dry ice. Twenty-eight laboratories participated in this study and provided 34 sets of results for the measurement of 25(OH)D using 20 ligand binding assays and 14 liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods. Equivalence of the assay response for the frozen versus ambient DEQAS samples for each assay was evaluated using multi-level modeling, paired t-tests including a false discovery rate (FDR) approach, and ordinary least squares linear regression analysis of frozen versus ambient results. Using the paired t-test and confirmed by FDR testing, differences in the results for the ambient and frozen samples were found to be statistically significant at p < 0.05 for four assays (DiaSorin, DIAsource, Siemens, and SNIBE prototype). For all 14 LC-MS/MS assays, the differences in the results for the ambient- and frozen-shipped samples were not found to be significant at p < 0.05 indicating that these analytes were stable during shipment at ambient conditions. Even though assay results have been shown to vary considerably among different 25(OH)D assays in other studies, the results of this study also indicate that sample handling/transport conditions may influence 25(OH)D assay response for several assays.

Assessment of serum total 25-hydroxyvitamin D assay commutability of Standard Reference Materials and College of American Pathologists Accuracy-Based Vitamin D (ABVD) Scheme and Vitamin D External Quality Assessment Scheme (DEQAS) materials: Vitamin D Standardization Program (VDSP) Commutability Study 2

An interlaboratory study was conducted through the Vitamin D Standardization Program (VDSP) to assess commutability of Standard Reference Materials® (SRMs) and proficiency testing/external quality assessment (PT/EQA) samples for determination of serum total 25-hydroxyvitamin D [25(OH)D] using ligand binding assays and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A set of 50 single-donor serum samples were assigned target values for 25-hydroxyvitamin D2 [25(OH)D2] and 25-hydroxyvitamin D3 [25(OH)D3] using reference measurement procedures (RMPs). SRM and PT/EQA samples evaluated included SRM 972a (four levels), SRM 2973, six College of American Pathologists (CAP) Accuracy-Based Vitamin D (ABVD) samples, and nine Vitamin D External Quality Assessment Scheme (DEQAS) samples. Results were received from 28 different laboratories using 20 ligand binding assays and 14 LC-MS/MS methods. Using the test assay results for total serum 25(OH)D (i.e., the sum of 25(OH)D2 and 25(OH)D3) determined for the single-donor samples and the RMP target values, the linear regression and 95% prediction intervals (PIs) were calculated. Using a subset of 42 samples that had concentrations of 25(OH)D2 below 30 nmol/L, one or more of the SRM and PT/EQA samples with high concentrations of 25(OH)D2 were deemed non-commutable using 5 of 11 unique ligand binding assays. SRM 972a (level 4), which has high exogenous concentration of 3-epi-25(OH)D3, was deemed non-commutable for 50% of the LC-MS/MS assays.

Performance Characteristics of the Vidas SARS-CoV-2 IgM and IgG Serological Assays

The COVID-19 pandemic, caused by the new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), continues to spread worldwide. Serological testing for SARS-CoV-2-specific antibodies plays an important role in understanding and controlling the pandemic, notably through epidemiological surveillance. Well-validated and highly specific SARS-CoV-2 serological assays are urgently needed. We describe here the analytical and clinical performance of Vidas SARS-CoV-2 IgM and Vidas SARS-CoV-2 IgG, two CE-marked, emergency use authorization (EUA)-authorized, automated, qualitative assays for the detection of SARS-CoV-2-specific IgM and IgG, respectively. Both assays showed high within-run and within-laboratory precision (coefficients of variation < 11.0%) and very low cross-reactivity toward sera of patients with a past common coronavirus or respiratory virus infection. Clinical specificity determined on up to 989 prepandemic healthy donors was ≥99% with a narrow 95% confidence interval for both IgM and IgG assays. Clinical sensitivity was determined on up to 232 samples from 130 reverse transcriptase PCR (RT-PCR)-confirmed SARS-CoV-2 patients. The positive percent agreement (PPA) with SARS-CoV-2 PCR reached 100% at ≥16 days (Vidas SARS-CoV-2 IgM) and ≥32 days (Vidas SARS-CoV-2 IgG) of symptom onset. Combined IgM/IgG test results improved the PPA compared to each test alone. SARS-CoV-2 IgG seroconversion followed closely that of SARS-CoV-2 IgM and remained stable over time, while SARS-CoV-2 IgM levels rapidly declined. Interestingly, SARS-CoV-2-specific IgM and IgG responses were significantly higher in COVID-19 hospitalized versus nonhospitalized patients. Altogether, the Vidas SARS-CoV-2 IgM and IgG assays are highly specific and sensitive serological tests suitable for the reliable detection of past acute SARS-CoV-2 infections.

Nucleotide sequence comparison of the 3' terminal region of the genome of pepper vein mottle virus isolates from Tunisia and Ivory Coast

Three Tunisian PVMV isolates identified in pepper and tomato fields and one isolate from Ivory Coast were submitted to biological and molecular analysis. Phenotypically, Tunisian isolates induced mild symptoms while the Ivory Coast one is more aggressive on tobacco. As no PVMV sequence data are available, detailed sequence comparisons of coat protein gene (CP) were made. No nucleotide or amino acid changes in this region could be related to the pathogenicity of the isolates analysed. With the aim to increase our molecular understanding of the biological properties, we have sequenced the 3'-non translated region (3'NTR). Results suggest that this region of the RNA genome may be involved in the modulation of disease symptoms.

Plant lipoxygenase 2 is a translation initiation factor-4E-binding protein

The eukaryotic initiation factor 4E (eIF4E) emerged recently as a target for different types of regulation affecting translation. In animal and yeast cells, eIF4E-binding proteins modulate the availability of eIF4E. A search for plant eIF4E-binding proteins from Arcabictopsis thaliana using the yeast genetic interaction system identified a clone encoding a lipoxygenase type 2 (AtLOX2). In vitro and in vivo biochemical assays confirm an interaction between AtLOX2 and plant eIF4E(iso) factor. A two-hybrid assay revealed that AtLOX2 is also able to interact with both wheat initiation factors 4E and 4E(iso). Deletion analysis maps the region of AtLOX2 involved in interaction with AteIF(iso)4E between amino acids 175 and 232. A sequence related to the conserved motif present in several eIF4E-binding proteins was found in this region. Furthermore, the wheat p86 subunit, a component of the plant translation eIF(iso)4F complex, was found to interfere with the AteIF(iso)4E-AtLOX2 interaction suggesting that p86 and AtLOX2 compete for the same site on eIF(iso)4E. These results may reflect a link between eIF4Es factors mediating translational control with LOX2 activity, which is probably conserved throughout the plant kingdom.

Synthesis of (-)-strand RNA from the 3' untranslated region of plant viral genomes expressed in transgenic plants upon infection with related viruses

When expressed in transgenic tobacco plants, transgene mRNA that includes the 3' untranslated region (3' UTR) of Lettuce mosaic virus served as template for synthesis of complementary (-)-strand RNA following an infection by Tobacco etch virus, Tobacco vein mottle virus or Pepper mottle virus, but not when infected with Cucumber mosaic virus. Deletion of the 3' UTR from the transgene abolished the synthesis of (-)-strand transcripts. Similar results were obtained in transgenic tobacco plants expressing mRNA that includes the RNA3 3' UTR of Cucumber mosaic virus when infected with Tomato aspermy virus. These results show that the viral RNA-dependent RNA polymerase of several potyviruses and Tomato aspermy virus have the ability to recognize heterologous 3' UTRs when included in transgene mRNAs, and to use them as transcription promoters.

Restriction maps and homologies of the three plasmids of Agrobacterium rhizogenes strain A4

Agrobacterium rhizogenes strain A4 is a virulent agropine-type strain possessing three plasmids: plasmid a (pArA4a, 180 kb) is not necessary for plant transformation, plasmid b (250 kb) is the root-inducing plasmid (pRiA4), and plasmid c (pArA4c) is a cointegrate of pArA4a and pRiA4. The total plasmid DNA (pArA4) of strain A4 was cloned in the cosmid pHSG262 and the library obtained was used to establish BamHI maps of the three plasmids. The plasmids a and Ri have an apparently identical region and a partly homologous region, and are different in the remaining regions including their origins of replication. Another agropine-type A. rhizogenes strain, HRI, bears only one plasmid, which is the Ri plasmid (pRiHRI). pRiHRI and pRiA4 present the same restriction maps for a great part, but are different in a region of 48 kb; however, this region of pRiHRI is found unmodified in pArA4a and may have a role in the virulence of the bacteria. The comparison between the restriction maps of the plasmids of strain A4 leads us to propose that the recombination event leading to pArA4c formation occurs within the identical regions of pArA4a and pRiA4. In addition, the comparison with the already established map of pRiHRI suggests that strain HRI could have been derived from a recombination event between the two homologous regions of pArA4c with subsequent loss of the smaller plasmid.