An Overview of Current Approaches Toward the Treatment and Prevention of West Nile Virus Infection

Emerging Disease of the Desert: Rise of West Nile Virus Chorioretinitis in Arizona

Purpose: To present 7 cases of West Nile virus (WNV)-related chorioretinitis in Arizona. Methods: Retina clinic charts with the terms "chorioretinitis" and "West Nile" were selected from April 1, 2012, to February 1, 2023. Results: Seven patients with initial visits between August 2019 and February 2023 were included. The majority of WNV chorioretinitis cases were seen in the last 4 years of the selected dates. Only 1 patient presented before this time but was excluded for inadequate baseline testing. All 7 patients had hospitalization for neuroinvasive disease before clinical presentation. All patients achieved a final visual acuity of 20/25 to 20/70. Conclusions: In the last 4 years of the study period, an uptrend in WNV chorioretinitis was found in our retina clinics in Arizona, reflecting the overall rise in WNV outbreaks across the state. As WNV continues to rise, the eye specialist should have high suspicion for WNV ocular disease, even in states where WNV had been an uncommon entity.

Bilateral Upper Extremity Tremors in West Nile Encephalitis

West Nile encephalitis is a rare complication of infection from the West Nile virus (WNv). Viral encephalitis can mimic manifestations of other neurologic diseases. The purpose of this article is to report a case of a 60-year-old female who developed bilateral upper extremity tremors with West Nile encephalitis. She presented to a hospital in Southern Louisiana with persistent high fevers and new onset confusion. She soon developed tremors which persisted throughout her hospitalization. Computerized tomography (CT) of the head revealed no abnormalities. Cerebral spinal fluid (CSF) was remarkable for WNv IgM, and supportive care was pursued. After nearly three weeks, she was transferred to a skilled nursing facility for further care. The presentation of movement disorder with confusion usually raises concern for injury to the brain or spinal cord or other neurologic illnesses. Despite the presentation of movement disorders or other neurologic manifestations, viral etiologies should remain high on the differential when the patient has additional symptoms, such as fever and elevated white blood cell (WBC) count, to limit inappropriate diagnostic testing and treatment.

Identification of West Nile virus RNA-dependent RNA polymerase non-nucleoside inhibitors by real-time high throughput fluorescence screening

West Nile virus (WNV) is a re-emergent mosquito-borne RNA virus that causes major outbreaks of encephalitis around the world. However, there is no therapeutic treatment to struggle against WNV, and the current treatment relies on alleviating symptoms. Therefore, due to the threat virus poses to animal and human health, there is an urgent need to come up with fast strategies to identify and assess effective antiviral compounds. A relevant target when developing drugs against RNA viruses is the viral RNA-dependent RNA polymerase (RdRp), responsible for the replication of the viral genome within a host cell. RdRps are key therapeutic targets based on their specificity for RNA and their essential role in the propagation of the infection. We have developed a fluorescence-based method to measure WNV RdRp activity in a fast and reliable real-time way. Interestingly, rilpivirine has shown in our assay inhibition of the WNV RdRp activity with an IC₅₀ value of 3.3 μM and its antiviral activity was confirmed in cell cultures. Furthermore, this method has been extended to build up a high-throughput screening platform to identify WNV polymerase inhibitors. By screening a small chemical library, novel RdRp inhibitors 1-4 have been identified. When their antiviral activity was tested against WNV in cell culture, 4 exhibited an EC₅₀ value of 2.5 μM and a selective index of 12.3. Thus, rilpivirine shows up as an interesting candidate for repurposing against flavivirus. Moreover, the here reported method allows the rapid identification of new WNV RdRp inhibitors.

Introduction to West Nile Virus

West Nile virus (WNV) is a mosquito-borne, single-stranded, positive-sense RNA virus belonging to the Flaviviridae family. After WNV gains entry through an infected mosquito bite, it replicates in a variety of human cell types and produces a viremia. Although the majority of infected individuals remain asymptomatic, the manifested symptoms in some people range from a mild fever to severe neurological disorder with high morbidity and mortality. In addition, many who recover from WNV neuroinvasive infection present with long-term deficits, including weakness, fatigue, and cognitive problems. Since entering the USA in 1999, WNV has become the most common mosquito-borne virus in North America. Despite the intensive research over 20 years, there are still no approved vaccines or specific treatments for humans, and it remains an urgent need to understand the pathogenesis of WNV and develop specific therapeutics and vaccines.

Plant-Based Natural Products and Extracts: Potential Source to Develop New Antiviral Drug Candidates

Viral infections are among the most complex medical problems and have been a major threat to the economy and global health. Several epidemics and pandemics have occurred due to viruses, which has led to a significant increase in mortality and morbidity rates. Natural products have always been an inspiration and source for new drug development because of their various uses. Among all-natural sources, plant sources are the most dominant for the discovery of new therapeutic agents due to their chemical and structural diversity. Despite the traditional use and potential source for drug development, natural products have gained little attention from large pharmaceutical industries. Several plant extracts and isolated compounds have been extensively studied and explored for antiviral properties against different strains of viruses. In this review, we have compiled antiviral plant extracts and natural products isolated from plants reported since 2015.

Role of autophagy during the replication and pathogenesis of common mosquito-borne flavi- and alphaviruses

Arboviruses that are transmitted to humans by mosquitoes represent one of the most important causes of febrile illness worldwide. In recent decades, we have witnessed a dramatic re-emergence of several mosquito-borne arboviruses, including dengue virus (DENV), West Nile virus (WNV), chikungunya virus (CHIKV) and Zika virus (ZIKV). DENV is currently the most common mosquito-borne arbovirus, with an estimated 390 million infections worldwide annually. Despite a global effort, no specific therapeutic strategies are available to combat the diseases caused by these viruses. Multiple cellular pathways modulate the outcome of infection by either promoting or hampering viral replication and/or pathogenesis, and autophagy appears to be one of them. Autophagy is a degradative pathway generally induced to counteract viral infection. Viruses, however, have evolved strategies to subvert this pathway and to hijack autophagy components for their own benefit. In this review, we will focus on the role of autophagy in mosquito-borne arboviruses with emphasis on DENV, CHIKV, WNV and ZIKV, due to their epidemiological importance and high disease burden.

Evaluation of sofosbuvir activity and resistance profile against West Nile virus in vitro

Sofosbuvir, a licensed nucleotide analog targeting hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp), has been recently evaluated as a broad anti-Flavivirus lead candidate revealing activity against Zika and Dengue viruses both in vitro and in animal models. In this study, the in vitro antiviral activity of sofosbuvir against West Nile virus (WNV) was determined by plaque assay (PA) and Immunodetection Assay (IA) in human cell lines and by enzymatic RdRp assay. By PA, the sofosbuvir half-maximal inhibitory concentration (IC₅₀) was 1.2 ± 0.3 μM in Huh-7, 5.3 ± 0.9 μM in U87, 7.8 ± 2.5 μM in LN-18 and 63.4 ± 14.1 μM in A549 cells. By IA, anti-WNV activity was confirmed in both hepatic (Huh-7, 1.7 ± 0.5 μM) and neuronal (U87, 7.3 ± 2.0 μM) cell types. Sofosbuvir was confirmed to inhibit the purified WNV RdRp (IC₅₀ 11.1 ± 4.6 μM). In vitro resistance selection experiments were performed by propagating WNV in the Huh-7 cell line with two-fold increasing concentrations of sofosbuvir. At 80 μM, a significantly longer time for viral breakthrough was observed compared with lower concentrations (18 vs. 7-9 days post infection; p = 0.029), along with the detection of the S604T mutation, corresponding to the well-known S282T substitution in the motif B of HCV NS5B, which confers resistance to sofosbuvir. Molecular docking experiments confirmed that the S604T mutation within the catalytic site of RdRp affected the binding mode of sofosbuvir. To our knowledge, this is the first report of the antiviral activity of sofosbuvir against WNV as well as of selection of mutants in vitro.

Biochemistry and Molecular Biology of Flaviviruses

Flaviviruses, such as dengue, Japanese encephalitis, tick-borne encephalitis, West Nile, yellow fever, and Zika viruses, are critically important human pathogens that sicken a staggeringly high number of humans every year. Most of these pathogens are transmitted by mosquitos, and not surprisingly, as the earth warms and human populations grow and move, their geographic reach is increasing. Flaviviruses are simple RNA-protein machines that carry out protein synthesis, genome replication, and virion packaging in close association with cellular lipid membranes. In this review, we examine the molecular biology of flaviviruses touching on the structure and function of viral components and how these interact with host factors. The latter are functionally divided into pro-viral and antiviral factors, both of which, not surprisingly, include many RNA binding proteins. In the interface between the virus and the hosts we highlight the role of a noncoding RNA produced by flaviviruses to impair antiviral host immune responses. Throughout the review, we highlight areas of intense investigation, or a need for it, and potential targets and tools to consider in the important battle against pathogenic flaviviruses.

Small Interfering RNA-Mediated Control of Virus Replication in the CNS Is Therapeutic and Enables Natural Immunity to West Nile Virus

No vaccines or therapeutics are licensed for West Nile virus (WNV), a mosquito-transmitted neuroencephalitic flavivirus. The small interfering RNA siFvE^JW targets a conserved sequence within the WNV E protein and limits virus infection. Using a rabies virus-derived neuron-targeting peptide (RVG9R) and an intranasal route for delivering siFvE^JW to the CNS, we demonstrate that treatment of WNV-infected mice at late stages of neuroinvasive disease results in recovery. Selectively targeting virus in the CNS lowers viral burdens in the brain, reduces neuropathology, and results in a 90% survival rate at 5-6 days post-infection (when viral titers peak in the CNS), while placebo-treated mice succumb by days 9-10. Importantly, CNS virus clearance is achieved by humoral and cell-mediated immune responses to WNV infection in peripheral tissues, which also engender sterilizing immunity against subsequent WNV infection. These results indicate that intranasal RVG9R-siRNA treatment offers efficient late-stage therapy and facilitates natural long-term immunity against neuroinvasive flaviviruses.