Comparison of surface plasmon resonance, resonant waveguide grating biosensing and enzyme linked immunosorbent assay (ELISA) in the evaluation of a dengue virus immunoassay.

Two label-free biosensor platforms, Resonance Waveguide Grating (RWG) and Surface Plasmon Resonance (SPR), were used to rank a large panel of anti-dengue virus NS1 antibodies. Dengue non-structural 1 (NS1) protein is an established serological marker for the early detection of dengue infection. A variety of commercial dengue NS1 antigen capture immunoassays are available in both ELISA and lateral flow format. However, there is a significant scope to improve both the sensitivity and the specificity of those tests. The interactions of antibody (Ab)-antigen (Ag) were profiled, with weak interactions (KD = 1-0.1 µM) able to be detected under static equilibrium conditions by RWG, but not observed to under more rigorous flow conditions using SPR. There were significant differences in the absolute affinities determined by the two technologies, and there was a poor correlation between antibodies best ranked by RWG and the lower limit of detection (LLOD) found by ELISA. Hence, whilst high-throughput RWG can be useful as preliminary screening for higher affinity antibodies, care should be exercised in the assignation of quantitative values for affinity between different assay formats.

The diagnostic sensitivity of dengue rapid test assays is significantly enhanced by using a combined antigen and antibody testing approach.

BACKGROUND: Serological tests for IgM and IgG are routinely used in clinical laboratories for the rapid diagnosis of dengue and can differentiate between primary and secondary infections. Dengue virus non-structural protein 1 (NS1) has been identified as an early marker for acute dengue, and is typically present between days 1-9 post-onset of illness but following seroconversion it can be difficult to detect in serum. AIMS: To evaluate the performance of a newly developed Panbio® Dengue Early Rapid test for NS1 and determine if it can improve diagnostic sensitivity when used in combination with a commercial IgM/IgG rapid test. METHODOLOGY: The clinical performance of the Dengue Early Rapid was evaluated in a retrospective study in Vietnam with 198 acute laboratory-confirmed positive and 100 negative samples. The performance of the Dengue Early Rapid in combination with the IgM/IgG Rapid test was also evaluated in Malaysia with 263 laboratory-confirmed positive and 30 negative samples. KEY RESULTS: In Vietnam the sensitivity and specificity of the test was 69.2% (95% CI: 62.8% to 75.6%) and 96% (95% CI: 92.2% to 99.8) respectively. In Malaysia the performance was similar with 68.9% sensitivity (95% CI: 61.8% to 76.1%) and 96.7% specificity (95% CI: 82.8% to 99.9%) compared to RT-PCR. Importantly, when the Dengue Early Rapid test was used in combination with the IgM/IgG test the sensitivity increased to 93.0%. When the two tests were compared at each day post-onset of illness there was clear differentiation between the antigen and antibody markers. CONCLUSIONS: This study highlights that using dengue NS1 antigen detection in combination with anti-glycoprotein E IgM and IgG serology can significantly increase the sensitivity of acute dengue diagnosis and extends the possible window of detection to include very early acute samples and enhances the clinical utility of rapid immunochromatographic testing for dengue.

BDNF increases homotypic olivocerebellar reinnervation and associated fine motor and cognitive skill.

Recovery of complex neural function after injury to the adult CNS is limited by minimal spontaneous axonal regeneration and/or sprouting from remaining pathways. In contrast, the developing CNS displays spontaneous reorganization following lesion, in which uninjured axons can develop new projections to appropriate target neurons and provide partial recovery of complex behaviours. Similar pathways can be induced in the mature CNS, providing models to optimize post-injury recovery of complex neural functions. After unilateral transection of a developing olivocerebellar path (pedunculotomy), remaining inferior olivary axons topographically reinnervate the denervated hemicerebellum and compensate functional deficits. Brain-derived neurotrophic factor (BDNF) partly recreates such reinnervation in the mature cerebellum. However the function of this incomplete reinnervation and any unwanted behavioural effects of BDNF remain unknown. We measured olivocerebellar reinnervation and tested rotarod and navigation skills in Wistar rats treated with BDNF/vehicle and pedunculotomized on day 3 (Px3; with reinnervation) or 11 (Px11; without spontaneous reinnervation). BDNF treatment did not affect motor or spatial behaviour in normal (control) animals. Px11-BDNF animals equalled controls on the rotarod, outperforming Px11-vehicle animals. Moreover, Px3-BDNF and Px11-BDNF animals achieved spatial learning and memory tasks as well as controls, with Px11-BDNF animals showing better spatial orientation than Px11-vehicle counterparts. BDNF slightly increased olivocerebellar reinnervation in Px3 animals and induced sparse (22% Purkinje cells) yet widespread reinnervation in Px11 animals. As reinnervation correlated with spatial function, these data imply that after injury even a small amount of reinnervation that is homotypic to correct target neurons compensates deficits in appropriate complex motor and spatial skills. As there was no effect in control animals, BDNF effectively induces this axon collateralisation without interfering with normal neuronal circuits.

Maternal antibody and viral factors in the pathogenesis of dengue virus in infants.

The pathogenesis of dengue in infants is poorly understood. We postulated that dengue severity in infants would be positively associated with markers of viral burden and that maternally derived, neutralizing anti-dengue antibody would have decayed before the age at which infants with dengue presented to the hospital. In 75 Vietnamese infants with primary dengue, we found significant heterogeneity in viremia and NS1 antigenemia at hospital presentation, and these factors were independent of disease grade or continuous measures of disease severity. Neutralizing antibody titers, predicted in each infant at the time of their illness, suggested that the majority of infants (65%) experienced dengue hemorrhagic fever when the maternally derived neutralizing antibody titer had declined to <1 : 20. Collectively, these data have important implications for dengue vaccine research because they suggest that viral burden may not solely explain severe dengue in infants and that neutralizing antibody is a reasonable but not absolute marker of protective immunity in infants.

Prevalence and effect of spawner-isolated mortality virus on the hatchery phases of Penaeus monodon and P. merguiensis in Australia.

Spawner-isolated mortality virus (SMV) has been associated with mortalities in broodstock of Penaeus monodon and with mid-crop mortality syndrome on grow-out farms. Epidemiological evidence suggested an association between the SMV status of broodstock and subsequent survival of their progeny, and this paper describes investigations into that association. The faeces of 909 broodstock in 9 different groups were tested by a polymerase chain reaction (PCR) for SMV and positive results were confirmed by an internal dot-blot. Seventy-seven spawners (8.5%) were positive for SMV with prevalence ranging from 0 to 24% among groups. The prevalence in spawners of P. monodon was higher (24%) than in P. merguiensis (4%). Three longitudinal studies were undertaken to compare the survival of progeny from broodstock that were positive to SMV with those that were not. Survival in hatchery tanks of progeny from SMV-positive spawners was lower than those from SMV-negative spawners with reductions of 23% (p = 0.01), 7.3% (p = 0.214) and 18.9% (p = 0.129) in the 3 studies. The conclusions were less consistent when examined during each of the later stages of growth in hatchery pools, nursery and grow-out ponds, with progeny from SMV-postive spawners sometimes having better survival rates. However, survival was better overall in progeny from SMV-negative spawners. Simple linear regression showed survival was negatively related to the proportion of postlarvae from SMV-positive spawners, with a decrease in survival of 5.6% for each 10% increase in the proportion of postlarvae coming from SMV-positive spawners (p = 0.006). Data from 38 ponds showed 6.71% of losses were due to SMV. If these losses were consistent across the entire industry, the annual loss due to SMV would have been approximately AUD 3 million in 1999/2000.

Analogous cytokine responses to Burkholderia pseudomallei strains contrasting in virulence correlate with partial cross-protection in immunized mice.

Cytokine mRNA levels were assessed in Burkholderia pseudomallei-susceptible BALB/c mice and B. pseudomallei-resistant C57BL/6 mice following administration of a sublethal dose of less virulent (LV) B. pseudomallei, a candidate immunogen tested for protection against a highly virulent (HV) challenge. Compared on the basis of the bacterial loads, the cytokine patterns induced by HV and LV B. pseudomallei were similar, involving gamma interferon, interleukin-10, and other cytokines. Partial cross-protection between B. pseudomallei strains is shown to be associated with cytokine profiles involving both type 1 and type 2 cytokines.