Evaluation and optimization of SYBR Green real-time reverse transcription polymerase chain reaction as a tool for diagnosis of the Flavivirus genus in Brazil

Rocio Virus: An Updated View on an Elusive Flavivirus

Rocio virus (ROCV) is a mosquito-borne flavivirus and human pathogen. The virus is indigenous to Brazil and was first detected in 1975 in the Sao Paulo State, and over a period of two years was responsible for several epidemics of meningoencephalitis in coastal communities leading to over 100 deaths. The vast majority of ROCV infections are believed to be subclinical and clinical manifestations can range from uncomplicated fever to fatal meningoencephalitis. Birds are the natural reservoir and amplification hosts and ROCV is maintained in nature in a mosquito-bird-mosquito transmission cycle, primarily involving Psorophora ferox mosquitoes. While ROCV has remained mostly undetected since 1976, in 2011 it re-emerged in Goiás State causing a limited outbreak. Control of ROCV outbreaks depends on sustainable vector control measures and public education. To date there is no specific treatment or licensed vaccine available. Here we provide an overview of the ecology, transmission cycles, epidemiology, pathogenesis, and treatment options, aiming to improve our ability to understand, predict, and ideally avert further ROCV emergence.

Applying a pan-flavivirus RT-qPCR assay in Brazilian public health surveillance

The aim of this study was to improve flavivirus field monitoring in Brazil using a reliable probe-based RT-qPCR assay. Standard flavivirus strains were employed to evaluate the performance of the assay, and its applicability was evaluated using 235 stored pools of Culicidae samples collected between 1993 and 1997 and in 2016. Flavivirus species were identified by sequencing. Sixteen (6.8%) samples tested positive: Ilheus virus, Iguape virus, and Saint Louis encephalitis virus were identified in historical specimens from 1993-1994, while insect-specific flaviviruses were detected in the samples from 2016. This approach was demonstrated to be accurate for flavivirus detection and characterization, and it can be successfully applied for vector surveillance and for monitoring and discovery of insect specific flaviviruses.

Evaluation of six TaqMan RT-rtPCR kits on two thermocyclers for the reliable detection of rabies virus RNA

Rabies is diagnosed postmortem in animals, based on tests prescribed by the World Organization for Animal Health (OIE), such as the fluorescent antibody test, the direct rapid immunohistochemistry test, or pan-lyssavirus PCR assays. Several reverse-transcription real-time PCR (RT-rtPCR) methods have been developed and validated for rapid and accurate detection of lyssaviruses. We evaluated the performance of 6 TaqMan RT-rtPCR kits using different commercial master mixes and 2 real-time thermocyclers. Changing the master mix overall did not influence the TaqMan RT-rtPCR performance, regardless of the thermocycler used. The limits of detection at the 95% confidence level were 18.1-25.8 copies/µL for the Rotor-Gene Q MDx thermocycler and 16.7-21.5 for the Mx3005P thermocycler. Excellent repeatability was demonstrated for rabies virus (RABV) RNA samples of 100, 50, and 25 copies/µL regardless of the thermocycler used. RABV field samples ( n = 35) isolated worldwide gave positive results using the most efficient of the 6 kits tested, with a copy number of 6.03 × 10² to 6.78 × 10⁷ RNA copies per reaction. The TaqMan RT-rtPCR assay provides sensitive and rapid amplification of RABV RNA.

Evaluating the use of fluorescence-based flow cytometry assay for dengue diagnosis using peripheral blood mononuclear cells

INTRODUCTION

Dengue virus (DENV) is the most important arthropod-borne viral disease worldwide with an estimated 50 million infections occurring each year.

METHODS

In this study, we present a flow cytometry assay (FACS) for diagnosing DENV, and compare its results with those of the non-structural protein 1 (NS1) immunochromatographic assay and reverse transcriptase polymerase chain reaction (RT-PCR).

RESULTS

All three assays identified 29.1% (39/134) of the patients as dengue-positive. The FACS approach and real-time RT-PCR detected the DENV in 39 and 44 samples, respectively. On the other hand, the immunochromatographic assay detected the NS1 protein in 40.1% (56/134) of the patients. The Cohen's kappa coefficient analysis revealed a substantial agreement among the three methods.

CONCLUSIONS

The FACS approach may be a useful alternative for dengue diagnosis and can be implemented in public and private laboratories.