Neutralizing Dengue Antibody in Pregnant Thai Women and Cord Blood

<div><p>Background</p><p>The WHO ‘Global Strategy for Dengue Prevention and Control, 2012–2020’ addresses the growing need for the treatment of dengue, and targets a 25% reduction in morbidity and 50% in mortality (using 2010 estimates as baseline). Achieving these goals requires future dengue prevention strategies that will employ both potential vaccines and sustainable vector-control measures. Maternally transferred dengue antibody is an important factor in determining the optimal age for dengue vaccination.</p><p>Objectives</p><p>To estimate the seroprevalence of dengue antibodies among mothers living in an area of high endemicity – Ban Pong, Ratchaburi Province – and to assess maternal dengue antibodies transferred to cord blood.</p><p>Materials & Methods</p><p>A cross-sectional study was conducted with 141 pregnant women who delivered at Ban Pong Hospital, Ratchaburi, Thailand. Maternal-cord paired sera were tested for dengue neutralizing (NT) antibody by PRNT₅₀ assay. A ratio of ≥ 1:10 NT titer to dengue serotype was considered seropositive.</p><p>Results</p><p>Most mothers (137/141, 97.2%) had NT antibodies to at least one dengue serotype in their sera. At birth, the proportion of cord sera with NT antibodies to DEN-1, DEN-2, DEN-3, and DEN-4, were high and similar to the sera of their mothers, at 93.6%, 97.2%, 97.9%, and 92.2%, respectively. The dengue geometric mean titers (GMT) in cord blood were significantly higher than the maternal antibodies (p<0.001): highest in DEN-2, followed by DEN-3, and then DEN-1. The GMT of DEN-4 was the lowest among all four serotypes.</p><p>Conclusions</p><p>Dengue infection is highly prevalent among pregnant women in this dengue-endemic area. Most of the cord blood had transferred dengue antibodies, which may have an impact on the disease burden in this population.</p></div

Comparison of maternal dengue seroprevalence, maternal and cord sera dengue antibody titers in various articles.

<p>* p-values are based on paired sample t-test</p><p>^a range</p><p>^b mean±SD</p><p>^c mg/dL, GMT (range)</p><p>^d p-value 0.002 for DEN-1, 0.003 for DEN-3 and <0.001 for DEN-2 and DEN-4</p><p>^e p-value <0.001 for DEN-2 and DEN-3 only, p-value for DEN-1 and DEN-4 ≥ 0.5</p><p><i>n/a</i> = not applicable, <i>n</i>.<i>d</i>. <i>=</i> no data available</p><p>Comparison of maternal dengue seroprevalence, maternal and cord sera dengue antibody titers in various articles.</p

Demographic characteristics of 141 pregnant women.

<p>Demographic characteristics of 141 pregnant women.</p

Correlation between maternal and cord blood of DEN-1 to DEN-4 neutralizing antibodies titers.

<p>X-axis shows GMTs of cord blood dengue antibody and Y-axis shows GMTs of maternal dengue antibody of DEN-1, DEN-2, DEN-3 and DEN-4. The Spearman’s rho of DEN1, DEN2, DEN3 and DEN4 are 0.90, 0.92, 0.88 and 0.89 respectively.</p

The proportion and geometric mean titer of NT dengue antibodies of 141 maternal and cord paired sera.

<p>Note: p-values for comparisons of seroprevalence are based on symmetry test; p-values for comparisons of GMTs between mother and cord are based on paired test of log (NT)</p><p>The proportion and geometric mean titer of NT dengue antibodies of 141 maternal and cord paired sera.</p

Evaluation of a Dengue NS1 Antigen Detection Assay Sensitivity and Specificity for the Diagnosis of Acute Dengue Virus Infection

<div><p>Background</p><p>Currently, no dengue NS1 detection kit has regulatory approval for the diagnosis of acute dengue fever. Here we report the sensitivity and specificity of the InBios DEN Detect NS1 ELISA using a panel of well characterized human acute fever serum specimens.</p><p>Methodology/Principal Findings</p><p>The InBios DENV Detect NS1 ELISA was tested using a panel composed of 334 serum specimens collected from acute febrile patients seeking care in a Bangkok hospital in 2010 and 2011. Of these patients, 314 were found to have acute dengue by either RT-PCR and/or anti-dengue IgM/IgG ELISA. Alongside the InBios NS1 ELISA kit, we compared the performance characteristics of the BioRad Platelia NS1 antigen kit. The InBios NS1 ELISA Ag kit had a higher overall sensitivity (86% vs 72.8%) but equal specificity (100%) compared to the BioRad Platelia kit. The serological status of the patient significantly influenced the outcome. In primary infections, the InBios NS1 kit demonstrated a higher sensitivity (98.8%) than in secondary infections (83.5%). We found significant variation in the sensitivity of the InBios NS1 ELISA kit depending on the serotype of the dengue virus and also found decreasing sensitivity the longer after the onset of illness, showing 100% sensitivity early during illness, but dropping below 50% by Day 7.</p><p>Conclusion/Significance</p><p>The InBios NS1 ELISA kit demonstrated high accuracy when compared to the initial clinical diagnosis with greater than 85% agreement when patients were clinically diagnosed with dengue illness. Results presented here suggest the accurate detection of circulating dengue NS1 by the InBios DENV Detect NS1 ELISA can provide clinicians with a useful tool for diagnosis of early dengue infections.</p></div

Sensitivity of InBios and Bio-Rad assays based on clinical diagnosis and serological diagnosis.

a<p>Dengue Fever clinical diagnosis based on SEARO WHO guidelines <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003193#pntd.0003193-World1" target="_blank">[22]</a>.</p>b<p>Includes patients clinically diagnosed with DHF with plasma leakage, DSS and deaths based on SEARO WHO guidelines <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003193#pntd.0003193-World1" target="_blank">[22]</a>.</p>c<p>Total number of Dengue Fever equals 159, but 1 case could not be classified as primary or secondary infection.</p>d<p>Total number of Dengue Hemorrhagic Fever equals 141, but 1 case could not be classified as primary or secondary infection.</p><p>Sensitivity of InBios and Bio-Rad assays based on clinical diagnosis and serological diagnosis.</p

Sensitivity of InBios and Bio-Rad Assays stratified by date after onset of illness in (A) All infections and in (B) Primary and (C) Secondary infections.

<p>Serum samples (total samples, n = 314; primary, n = 51; secondary, n = 260) were tested using the InBios and Bio-Rad NS1 kits. Sensitivity was plotted against day post-onset of illness. p-values were calculated using McNemar's Chi-square test. NA – not applicable. Unable to do statistical analysis when value equals 0. NS – not significant.</p

Summary of study population.

a<p>IQR – interquartile range.</p>b<p>Represents subjects confirmed as dengue positive by serological testing only. The infecting serotype was unable to be determined since they were negative by RT-PCR.</p>c<p>Represents subjects confirmed as dengue positive by RT-PCR only. Serological studies were not positive and primary or secondary infection could not be determined.</p>d<p>Dengue Fever clinical diagnosis based on SEARO WHO guidelines <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003193#pntd.0003193-World1" target="_blank">[22]</a>.</p>e<p>Includes patients clinically diagnosed with DHF with plasma leakage, DSS and deaths based on SEARO WHO guidelines <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003193#pntd.0003193-World1" target="_blank">[22]</a>.</p>f<p>No diagnosis was given in 8 cases. Other clinical diagnoses included one each of bronchitis, gastritis, viral gastroenteritis, viral-induced thrombocytopenia, query rickettsial infection and nonspecific viral infection.</p><p>Summary of study population.</p

Overall performance characteristics of the InBios and Bio-Rad assays compared to reference standard^a.

a<p>The composite reference standard included samples that were positive either by serology and/or RT-PCR.</p>b<p>CI – confidence interval.</p>c<p>PPV – positive predictive value.</p>d<p>NPV – negative predictive value.</p>e<p>Sensitivity = (true positives)/(total positive by reference standard).</p>f<p>Specificity = (true negatives)/(total negative by reference standard).</p>g<p>Diagnostic Accuracy = (true positives+true negatives)/(total number of samples).</p>h<p>PPV = (true positives)/(total positive by InBios or Bio-Rad assay).</p>i<p>NPV = (true negatives)/(total negative by InBios or Bio-Rad assay).</p><p>Overall performance characteristics of the InBios and Bio-Rad assays compared to reference standard^{<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003193#nt107" target="_blank">a</a>}.</p