Methods for successful inactivation of Rift Valley fever virus in infected mosquitoes

Heat Treatment as a Safe-Handling Procedure for Rift Valley Fever Virus

Rift Valley Fever virus (RVFV) is a mosquito-borne virus with high pathogenic potential in ruminants and humans. Due to its high potential for spreading, it is considered a priority pathogen, and it is included in the Bluepoint list of the World Health Organization (WHO). Given the high pathogenic potential of the virus, it is crucial to develop a rapid heat-mediated inactivation protocol to create a safer working environment, particularly in medical facilities that lack a biosafety level 3 laboratory required for direct handling of RVFV. Our results reveal the broad tissue tropism of RVFV, showing the virus's capacity for replication in various cell lines. In terms of the thermal stability of RVFV, our findings showed that a 70 °C heat treatment did not fully inactivate the virus within 15 min. However, when exposed to 80 °C and 95 °C, the virus was completely inactivated after 15 min and 5 min, respectively. Additionally, our results indicated that heat-treatment only slightly decreased the integrity of the RVFV genome whether there is a high or low number of viral RNA copies. Overall, the study established a straightforward protocol for heat inactivation that may be beneficial in handling clinical and research samples of RVFV.

Effectiveness of TRIzol in Inactivating Animal Pathogens

Introduction

Safe handling of biological samples sourced from wild ecosystems is a pressing concern for scientists in disparate fields, including ecology and evolution, OneHealth initiatives, bioresources, geography, veterinary medicine, conservation, and many others. This is especially relevant given the growing global research community and collaborative networks that often span international borders. Treatments to inactivate potential pathogens of concern during transportation and analysis of biospecimens while preserving molecular structures of interest are necessary.

Objective

We provide a detailed resource on the effectiveness and limitations of TRIzol™ Reagent, a product commonly used in molecular biology to inactivate bacterial and viral pathogens found in wild animals.

Methods

By literature review, we evaluate the mode of action of TRIzol Reagent and its main components on bacterial and viral structures. We also synthesize peer-reviewed literature on the effectiveness of TRIzol in inactivating a broad range of infectious bacteria and viruses.

Key Findings

TRIzol Reagent inactivation is based on phenol, chaotropic salts, and sodium acetate. We find evidence of widespread efficacy in deactivating bacteria and a broad range of enveloped viruses. The efficacy against a subset of potential pathogens, including some nonenveloped viruses, remains uncertain.

Conclusion

Available evidence suggests that TRIzol Reagent is effective in inactivating a broad spectrum of bacteria and viruses from cells, tissues, and liquids in biological samples when the matrices are exposed to at least 10 min at room temperature to the reagent. We highlight areas that require additional research and discuss implications for laboratory protocols.

Laboratory demonstration of the vertical transmission of Rift Valley fever virus by Culex tarsalis mosquitoes

Rift Valley fever virus (RVFV) is a mosquito-transmitted virus with proven ability to emerge into naïve geographic areas. Limited field evidence suggests that RVFV is transmitted vertically from parent mosquito to offspring, but until now this mechanism has not been confirmed in the laboratory. Furthermore, this transmission mechanism has allowed for the prediction of RVFV epizootics based on rainfall patterns collected from satellite information. However, in spite of the relevance to the initiation of epizootic events, laboratory confirmation of vertical transmission has remained an elusive research aim for thirty-five years. Herein we present preliminary evidence of the vertical transmission of RVFV by Culex tarsalis mosquitoes after oral exposure to RVFV. Progeny from three successive gonotrophic cycles were reared to adults, with infectious RVFV confirmed in each developmental stage. Virus was detected in ovarian tissues of parental mosquitoes 7 days after imbibing an infectious bloodmeal. Infection was confirmed in progeny as early as the first gonotrophic cycle, with infection rates ranging from 2.0–10.0%. Virus titers among progeny were low, which may indicate a host mechanism suppressing replication.

Rift Valley fever virus (RVFV) represents a significant threat in terms of its ability to emerge into naïve geographic areas. Furthermore, RVFV represents a global public health risk due to the ability of many mosquito species to transmit the virus and the ease with which the virus can be transported due to increased globalization. The vertical transmission of RVFV by mosquitoes has long been accepted by the research community due to limited field evidence. However, laboratory confirmation of vertical transmission has remained elusive for thirty-five years. We present the first laboratory evidence of vertical transmission of RVFV in the susceptible North American vector, Culex tarsalis. We present two studies that clearly show 1) the accumulation of RVFV antigen in the ovaries of infected mosquitoes and 2) the transmission of RVFV from parent to offspring immediately following an infectious blood meal.

In Vitro Evaluation of Anti-Rift Valley Fever Virus, Antioxidant and Anti-Inflammatory Activity of South African Medicinal Plant Extracts

Rift valley fever virus (RVFV) is a mosquito-borne virus endemic to sub-Saharan African countries, and the first sporadic outbreaks outside Africa were reported in the Asia-Pacific region. There are no approved therapeutic agents available for RVFV; however, finding an effective antiviral agent against RVFV is important. This study aimed to evaluate the antiviral, antioxidant and anti-inflammatory activity of medicinal plant extracts. Twenty medicinal plants were screened for their anti-RVFV activity using the cytopathic effect (CPE) reduction method. The cytotoxicity assessment of the extracts was done before antiviral screening using the MTT assay. Antioxidant and reactive oxygen/nitrogen species' (ROS/RNS) inhibitory activity by the extracts was investigated using non-cell-based and cell-based assays. Out of twenty plant extracts tested, eight showed significant potency against RVFV indicated by a decrease in tissue culture infectious dose (TCID50) < 105. The cytotoxicity of extracts showed inhibitory concentrations values (IC50) > 200 µg/mL for most of the extracts. The antioxidant activity and anti-inflammatory results revealed that extracts scavenged free radicals exhibiting an IC50 range of 4.12-20.41 µg/mL and suppressed the production of pro-inflammatory mediators by 60-80% in Vero cells. This study demonstrated the ability of the extracts to lower RVFV viral load and their potency to reduce free radicals.

Methods of Inactivation of SARS-CoV-2 for Downstream Biological Assays

The scientific community has responded to the coronavirus disease 2019 (COVID-19) pandemic by rapidly undertaking research to find effective strategies to reduce the burden of this disease. Encouragingly, researchers from a diverse array of fields are collectively working towards this goal. Research with infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is undertaken in high-containment laboratories; however, it is often desirable to work with samples at lower-containment levels. To facilitate the transfer of infectious samples from high-containment laboratories, we have tested methods commonly used to inactivate virus and prepare the sample for additional experiments. Incubation at 80°C, a range of detergents, Trizol reagents, and UV energies were successful at inactivating a high titer of SARS-CoV-2. Methanol and paraformaldehyde incubation of infected cells also inactivated the virus. These protocols can provide a framework for in-house inactivation of SARS-CoV-2 in other laboratories, ensuring the safe use of samples in lower-containment levels.

Methods of inactivation of SARS-CoV-2 for downstream biological assays

The scientific community has responded to the COVID-19 pandemic by rapidly undertaking research to find effective strategies to reduce the burden of this disease. Encouragingly, researchers from a diverse array of fields are collectively working towards this goal. Research with infectious SARS-CoV-2 is undertaken in high containment laboratories, however, it is often desirable to work with samples at lower containment levels. To facilitate the transfer of infectious samples from high containment laboratories, we have tested methods commonly used to inactivate virus and prepare the sample for additional experiments. Incubation at 80°C, and a range of detergents and UV energies were successful at inactivating a high titre of SARS-CoV-2. These protocols can provide a framework for in house inactivation of SARS-CoV-2 in other laboratories, ensuring the safe use of samples in lower containment levels.