Diagnostic Specificity of Two Dengue Virus IgG ELISAs after Yellow Fever and Japanese Encephalitis Virus Vaccination

Dengue virus (DENV) antibody assays frequently cross-react with sera from individuals who have been infected with or vaccinated against related flaviviruses. The goal of this study was to determine the specificity of two DENV ELISAs with sera from individuals vaccinated against yellow fever virus (YFV) and Japanese encephalitis virus (JEV). The Panbio and the Novatec Dengue IgG ELISAs were tested with sera obtained 3-4 weeks or 0.5-6 years after YFV or JEV vaccination and the diagnostic specificity of the assays was determined. As controls, the sera were tested using DENV, YFV, JEV, Zika and West Nile virus neutralization assays. The diagnostic specificity of the Panbio and the Novatec ELISA with sera from YFV-vaccinated subjects was 98.2% and 88.2%, respectively. Cross-reactions were rare in the first 4 weeks despite high YFV-neutralizing antibody titers and were mostly found later. The specificity of the Panbio and Novatec assays with sera from JEV-vaccinated individuals was 100% and 92.9%. Cross-reactions occurred in the early time period after vaccination. The measurement values of the two ELISAs correlated strongly. Thus, the Panbio ELISA showed higher diagnostic specificity and may be suitable for seroprevalence studies in areas with high disease prevalence.

Enhancing the concordance of two commercial dengue IgG ELISAs by exchange of the calibrator sample

BACKGROUND

Dengue IgG testing is being recommended before dengue vaccination. Presently, the diagnostic method of choice is the dengue IgG ELISA.

OBJECTIVE

Determine the test performance and concordance of two commercial dengue IgG ELISA kits.

STUDY DESIGN

A diagnostic study to examine the sensitivity, specificity, accuracy and concordance of the Panbio Dengue Indirect IgG ELISA kit and the NovaLisa Dengue IgG ELISA kit. Sera (483) were from dengue-endemic regions in Sudan. Test performance characteristics were determined when tests were performed as indicated in the test kits and when the Panbio calibrator sample was used for both tests.

RESULTS

The sensitivity of the Panbio and the NovaLisa ELISA was 91.1% and 99.0% and the specificity was 79.4% and 50.9%. The Panbio test was slightly more accurate (87.5% compared with 84.0%). Quantitative measurement readings of the tests correlated. The calibrator samples gave different cutoff values. Replacing the NovaLisa cutoff sample with the Panbio calibrator sample raised the accuracy of the NovaLisa assay to 88% and increased the concordance of the tests from 82.8 to 93%.

CONCLUSIONS

The study shows that the two dengue IgG ELISAs differed clearly in sensitivity and specificity and gave discordant results for 17.2% of the sera. For the most part the discrepancy depended on the calibrator sample. The findings indicate that an optimized dengue IgG calibrator standard can enhance accuracy and concordance of commercial dengue ELISAs. An optimized standard calibrator would make dengue IgG seroprevalence testing more reliable.

High seroprevalence of dengue virus indicates that dengue virus infections are frequent in central and eastern Sudan

OBJECTIVES

To determine the seroprevalence of dengue in central and eastern Sudan and the breadth of neutralising antibody responses.

METHODS

Blood was drawn from 483 patients with fever who visited outpatient clinics in Port Sudan, Red Sea state, in three towns in Kassala state and in El Obeid, North Kordofan, in December 2012 and January 2013. Sera were tested for dengue virus IgG and IgM by ELISA (Panbio) and sera without serologic evidence of acute infection (IgM negative) were used for the analysis of the seroprevalence. DENV neutralisation tests were performed to determine the specificity of the ELISA and to examine the degree of cross-neutralisation of multiple DENV serotypes.

RESULTS

Sixty-seven per cent (302 of 448) of the sera were dengue virus IgG-positive. The seroprevalence in Port Sudan was 89% (106 of 119 sera), in Kassala 61% (128 of 209) and in North Kordofan 56.7% (68 of 120). Thirty-one of 32 ELISA-positive sera neutralised dengue viruses indicating that the ELISA was highly specific. The majority of the sera broadly neutralised all four dengue virus serotypes indicating multiple infections.

CONCLUSIONS

The majority of the population in central and eastern Sudan has been infected with dengue viruses, many people repeatedly. The high seroprevalence underscores the need for extended dengue surveillance in Sudan, broad disease awareness in medical institutions and in the population and diagnostic capacity building for severe dengue infections.

Magnetic resonance imaging analysis of anterior and posterior eye segment displacement during ocular gaze shifts

PURPOSE

To determine the relationship between movements of the posterior and anterior eye segments during arbitrary gaze shifts and to obtain information for monitoring fixation during radiotherapy for ocular diseases.

METHODS

We examined eye movements of ten emmetropic volunteers in a 1.5 T magnetic resonance system. Using a T2-weighted ultrafast turbo-spin echo sequence (UTSE), the eyes were examined within 21 seconds. Sagittal and transversal eye slices were obtained in five passages in five gaze directions (straight ahead, 15 degrees above, 15 degrees below, 15 degrees right and 15 degrees left of the primary position). Displacement of the posterior eye segment was analyzed in relation to the movement of the anterior segment in all directions.

RESULTS

The relationship between the movements of the anterior and posterior eye segment was 1:0.8 (+/- 0.06 SD) during horizontal gaze shifts and 1:1.16 (+/- 0.11 SD) during vertical gaze shifts.

CONCLUSIONS

Magnetic resonance imaging showed that the relationship between anterior and posterior eye segments was different during horizontal and vertical eye movements, indicating the presence of more than one center of rotation. Compared to the anterior eye segment, there was less displacement of the posterior eye segment during horizontal eye movements and more displacement during vertical eye movements.

Fixation monitoring during radiation therapy for subfoveal neovascularization

PURPOSE

The aim of the study was to determine movement of the fovea during each irradiation session by monitoring movement of the cornea. Knowing the extent of foveal deviation permits minimization of the field size.

METHODS

(1) Eye movement was monitored in 10 patients during irradiation. A TV camera with an attached fixation light was installed 3 cm away from the cornea of the treated eye. The fixation light was positioned at a 10 degrees angle to the TV camera on the opposite side of the gantry, resulting in a 90 degrees angle between the optical axis of the eye and the irradiation beam. (2) The relationship between movement of the anterior and posterior eye segments of 10 volunteers was examined using a scanning laser ophthalmoscope (SLO). Volunteers were asked to fix their gaze on positioning lights installed in the SLO. Gaze movements of the anterior and posterior eye segments were recorded simultaneously.

RESULTS

(1) The patients' ability to retain fixation differed interindividually. The median corneal deviation during 10 irradiation sessions was 1 mm mediolaterally and 0.7 mm craniocaudally. (2) Deviation of the fovea could be determined by monitoring deviation of the cornea. Measured by SLO, the correlation between movements of the anterior and posterior eye segments was 1:0.9 horizontally and 1:1.5 vertically.

CONCLUSION

(1) Irradiation field size can be reduced, depending on the patient's fixation stability. (2) If monitoring reveals a foveal deviation beyond the 95% isodose, irradiation can be interrupted.