Evaluation of dengue virus strains for human challenge studies.

Discordance between the measured levels of dengue virus neutralizing antibody and clinical outcomes in the first-ever efficacy study of a dengue tetravalent vaccine (Lancet, Nov 2012) suggests a need to re-evaluate the process of pre-screening dengue vaccine candidates to better predict clinical benefit prior to large-scale vaccine trials. In the absence of a reliable animal model and established correlates of protection for dengue, a human dengue virus challenge model may provide an approach to down-select vaccine candidates based on their ability to reduce risk of illness following dengue virus challenge. We report here the challenge of flavivirus-naïve adults with cell culture-passaged dengue viruses (DENV) in a controlled setting that resulted in uncomplicated dengue fever (DF). This sets the stage for proof-of-concept efficacy studies that allow the evaluation of dengue vaccine candidates in healthy adult volunteers using qualified DENV challenge strains well before they reach field efficacy trials involving children. Fifteen flavivirus-naïve adult volunteers received 1 of 7 DENV challenge strains (n=12) or placebo (n=3). Of the twelve volunteers who received challenge strains, five (two DENV-1 45AZ5 and three DENV-3 CH53489 cl24/28 recipients) developed DF, prospectively defined as ≥2 typical symptoms, ≥48h of sustained fever (>100.4°F) and concurrent viremia. Based on our study and historical data, we conclude that the DENV-1 and DENV-3 strains can be advanced as human challenge strains. Both of the DENV-2 strains and one DENV-4 strain failed to meet the protocol case definition of DF. The other two DENV-4 strains require additional testing as the illness approximated but did not satisfy the case definition of DF. Three volunteers exhibited effusions (1 pleural/ascites, 2 pericardial) and 1 volunteer exhibited features of dengue (rash, lymphadenopathy, neutropenia and thrombocytopenia), though in the absence of fever and symptoms. The occurrence of effusions in milder DENV infections counters the long-held belief that plasma leakage syndromes are restricted to dengue hemorrhagic fever/dengue shock syndromes (DHF/DSS). Hence, the human dengue challenge model may be useful not only for predicting the efficacy of vaccine and therapeutic candidates in small adult cohorts, but also for contributing to our further understanding of the mechanisms behind protection and virulence.

Improvements in amperometric detection of sulfite in food matrixes.

Sulfite is added to foods as an antimicrobial, antibrowning agent, or antioxidant. It also can occur naturally, and is often used in the production of beer and wine. For years the standard methodology for determination of sulfite in foods has been the Monier-Williams method, which is a combination of acid distillation and titration. Recently, AOAC adopted a chromatographic method based on a method developed by Kim and Kim for the determination of sulfite. The method combines ion exclusion chromatography with direct-current (DC) amperometric detection to provide more convenient and accurate quantitation of sulfite. However, fouling of the platinum working electrode results in a rapid decrease in method sensitivity. As a result, standards must be injected before and after every sample, and the electrode must be polished frequently to maintain adequate detection limits. Pulsed amperometric detection overcomes electrode fouling problems by repeatedly and continuously applying cleaning potentials to the working electrode. Using this technique, a reproducible electrode surface can be maintained, and injection-to-injection repeatability is greatly improved. A comparison of method performance for both DC and pulsed amperometric detection is presented. Also investigated was the stability of sulfite samples at varying pH, and in the presence or absence of a preservative.

Transition Temperatures of the Hydrates of Na2SO4, Na2HPO4, and KF as Fixed Points in Biomedical Thermometry.

The hydrate transition temperatures of Na2SO4·10H2O to Na2SO4, KF·2H2O to KF, and Na2HPO4·7H2O to Na2HPO4·2H2O were established using ACS grade salts as 32.374 °C, 41.422 °C, and 48.222 °C, respectively. A simple and reliable procedure involving inexpensive materials was used to realize these transitions as temperature fixed points. Each transition temperature was attained within 30 minutes of hydrate initiation and remained constant to within ±0.002 °C for more than 10 hours if the mixture was stirred. The established transition temperatures were sensitive at the 0.001 °C level to the amount of impurities, so the materials used should be of the highest quality available. These systems fill a gap in the existing spectrum of temperature standards and should be useful in biomedical laboratories for calibrating thermometers.