Flavivirus Persistence in Wildlife Populations

Diagnostic value of urine qRT-PCR for the diagnosis of West Nile virus neuroinvasive disease

Short and low-level viremia and virorachia, antibody cross-reactivity, IgM persistence, and inaccessibility of neutralization test, make laboratory diagnosis of West Nile virus (WNV) infection difficult. Recent investigations imply that WNV is excreted in urine longer and at higher concentrations compared to blood. The detection of WNV nucleic acid in cerebrospinal fluid (CSF), serum, and urine samples collected from 41 patients with suspected WNV neuroinvasive disease, was done by real-time RT-PCR assay. CSF and serum samples were also serologically tested using anti-WNV IgM/IgG ELISA kits. WNV infection was confirmed in 46.3% of patients by positive WNV RNA results in serum and/or CSF samples. The WNV RNA testing of urine allowed confirmation of 31.7% more cases. No association between WNV RNA urine positivity and age, gender, or the day of sample collection was found. The urine qRT-PCR can be a valuable diagnostic test for confirmation of probable cases of WNV neuroinvasive disease.

Isolation of Exosomes or Extracellular Vesicles from West Nile Virus-Infected N2a Cells, Primary Cortical Neurons, and Brain Tissues

Several flaviviruses compromise the blood-brain barrier integrity, infect the central nervous system, and elicit neuroinvasion to successfully cause neuropathogenesis in the vertebrate host. Therefore, understanding the pathway(s) and mechanism(s) to block the transmission and/or dissemination of flaviviruses and perhaps other neuroinvasive viruses is considered as an important area of research. Moreover, studies that address mechanism(s) of neuroinvasion by flaviviruses are limited. In this chapter, we discuss detailed methods to isolate exosomes or extracellular vesicles (EVs) from mouse and human N2a cells, primary cultures of murine cortical neurons, and mouse brain tissue. Two different methods including differential ultracentrifugation and density gradient exosome (DG-Exo) isolation are described for the preparation of exosomes/EVs from N2a cells and cortical neurons. In addition, we discuss the detailed DG-Exo method for the isolation of exosomes from murine brain tissue. Studies on neuronal exosomes will perhaps enhance our understanding of the mechanism of neuroinvasion by these deadly viruses.

The First Molecular Detection of Aedes albopictus in Sudan Associates with Increased Outbreaks of Chikungunya and Dengue

As part of our surveys of the invasive malaria vector Anopheles stephensi in four Sudanese states, including North and South Kordofan, Sennar, and White Nile, we collected 166 larvae. Our morphological identification confirmed that 30% of the collected mosquito samples were Anopheles species, namely An. gambiae s.l. and An. stephensi, while the 117 Aedes specimens were Ae. luteocephalus (39%), Ae. aegypti (32%), Ae. vexans (9%), Ae. vittatus (9%), Ae. africanus (6%), Ae. metalicus (3%), and Ae. albopictus (3%). Considering the serious threat of Ae. albopictus emergence for the public health in the area and our limited resources, we prioritized Ae. albopictus samples for further genomic analysis. We extracted the DNA from the three specimens and subsequently sequenced the cytochrome oxidase 1 (CO1) gene and confirmed their identity as Aedes albopictus and their potential origin by phylogenetic and haplotype analyses. Aedes albopictus, originating from Southeast Asia, is an invasive key vector of chikungunya and dengue. This is the first report and molecular characterization of Ae. albopictus from Sudan. Our sequences cluster with populations from the Central African Republic and La Réunion. Worryingly, this finding associates with a major increase in chikungunya and dengue outbreaks in rural areas of the study region and might be linked to the mosquito’s spread across the region. The emergence of Ae. albopictus in Sudan is of serious public health concern and urges for the improvement of the vector surveillance and control system through the implementation of an integrated molecular xenosurveillance. The threat of major arboviral diseases in the region underlines the need for the institutionalization of the One Health strategy for the prevention and control of future pandemics.

Potential Role of Flavivirus NS2B-NS3 Proteases in Viral Pathogenesis and Anti-flavivirus Drug Discovery Employing Animal Cells and Models: A Review

Flaviviruses are known to cause a variety of diseases in humans in different parts of the world. There are very limited numbers of antivirals to combat flavivirus infection, and therefore new drug targets must be explored. The flavivirus NS2B-NS3 proteases are responsible for the cleavage of the flavivirus polyprotein, which is necessary for productive viral infection and for causing clinical infections; therefore, they are a promising drug target for devising novel drugs against different flaviviruses. This review highlights the structural details of the NS2B-NS3 proteases of different flaviviruses, and also describes potential antiviral drugs that can interfere with the viral protease activity, as determined by various studies. Moreover, optimized in vitro reaction conditions for studying the NS2B-NS3 proteases of different flaviviruses may vary and have been incorporated in this review. The increasing availability of the in silico and crystallographic/structural details of flavivirus NS2B-NS3 proteases in free and drug-bound states can pave the path for the development of promising antiflavivirus drugs to be used in clinics. However, there is a paucity of information available on using animal cells and models for studying flavivirus NS2B-NS3 proteases, as well as on the testing of the antiviral drug efficacy against NS2B-NS3 proteases. Therefore, on the basis of recent studies, an effort has also been made to propose potential cellular and animal models for the study of flavivirus NS2B-NS3 proteases for the purposes of exploring flavivirus pathogenesis and for testing the efficacy of possible drugs targets, in vitro and in vivo.