Rift Valley fever virus: Unanswered questions

Countering Zoonotic Diseases: Current Scenario and Advances in Diagnostics, Monitoring, Prophylaxis and Therapeutic Strategies

Human life and health have interacted reciprocally with the surrounding environment and animal fauna for ages. This relationship is evident in developing nations, where human life depends more on the animal population for food, transportation, clothing, draft power, and fuel sources, among others. This inseparable link is a potent source of public health issues, especially in outbreaks of zoonotic diseases transmitted from animals to humans. Zoonotic diseases are referred to as diseases that are naturally transmitted between vertebrate animals and humans. Among the globally emerging diseases in the last decade, 75% are of animal origin, most of which are life-threatening. Since most of them are caused by potent new pathogens capable of long-distance transmission, the impact is widespread and has serious public health and economic consequences. Various other factors also contribute to the transmission, spread, and outbreak of zoonotic diseases, among which industrialization-led globalization followed by ecological disruption and climate change play a critical role. In this regard, all the possible strategies, including advances in rapid and confirmatory disease diagnosis and surveillance/monitoring, immunization/vaccination, therapeutic approaches, appropriate prevention and control measures to be adapted, and awareness programs, need to be adopted collaboratively among different health sectors in medical, veterinary, and concerned departments to implement the necessary interventions for the effective restriction, minimization, and timely control of zoonotic threats. The present review focuses on the current scenario of zoonotic diseases and their counteracting approaches to safeguard their health impact on humans.

HSP90 is part of a protein complex with the L polymerase of Rift Valley fever phlebovirus and prevents its degradation by the proteasome during the viral genome replication/transcription stage

The mosquito-borne Rift Valley fever virus (RVFV) from the Phenuiviridae family is a single-stranded RNA virus that causes the re-emerging zoonotic disease Rift Valley fever (RVF). Classified as a Category A agent by the NIH, RVFV infection can cause debilitating disease or death in humans and lead to devastating economic impacts by causing abortion storms in pregnant cattle. In a previous study, we showed that the host chaperone protein HSP90 is an RVFV-associated host factor that plays a critical role post viral entry, during the active phase of viral genome replication/transcription. In this study, we have elucidated the molecular mechanisms behind the regulatory effect of HSP90 during infection with RVFV. Our results demonstrate that during the early infection phase, host HSP90 associates with the viral RNA-dependent RNA polymerase (L protein) and prevents its degradation through the proteasome, resulting in increased viral replication.

Rift Valley fever in West Africa: A zoonotic disease with multiple socio-economic consequences

Rift Valley fever virus (RVFV) is an arbovirus that causes Rift Valley fever (RVF), a zoonotic disease that mainly affects domestic and wildlife ruminants and humans. The first epidemic in North-Western and West Africa occurred in Senegal and Mauritania in 1987, two countries where RVF is now endemic. Slaughterhouse workers, farmers, herders and veterinarians are at high risk of exposure to RVF. Beyond the health threat, RVF is considered to cause major socio-economic problems, specifically in developing countries where livestock farming and trade are important economic activities. Indeed, the mortality rate linked to RVF infection can reach 95-100% in newborns and young animals. In West Africa, livestock production is a key factor for food production and for national economics. Epizootics caused by RVF can therefore have serious socio-economic consequences by impacting multisectoral economics, the psycho-social health of pastoral communities, and food security. Improving prevention strategies against RVF, including vaccination, enhancing knowledge of RVF and correcting any inappropriate behaviors by populations of endemics areas, as well as better monitoring of RVF ecological factors are effective ways to better foresee and control outbreaks of RVF and its socio-economical side-effects in countries at high risk of occurrence of the disease.

Mechanistic models of Rift Valley fever virus transmission: A systematic review

Rift Valley fever (RVF) is a zoonotic arbovirosis which has been reported across Africa including the northernmost edge, South West Indian Ocean islands, and the Arabian Peninsula. The virus is responsible for high abortion rates and mortality in young ruminants, with economic impacts in affected countries. To date, RVF epidemiological mechanisms are not fully understood, due to the multiplicity of implicated vertebrate hosts, vectors, and ecosystems. In this context, mathematical models are useful tools to develop our understanding of complex systems, and mechanistic models are particularly suited to data-scarce settings. Here, we performed a systematic review of mechanistic models studying RVF, to explore their diversity and their contribution to the understanding of this disease epidemiology. Researching Pubmed and Scopus databases (October 2021), we eventually selected 48 papers, presenting overall 49 different models with numerical application to RVF. We categorized models as theoretical, applied, or grey, depending on whether they represented a specific geographical context or not, and whether they relied on an extensive use of data. We discussed their contributions to the understanding of RVF epidemiology, and highlighted that theoretical and applied models are used differently yet meet common objectives. Through the examination of model features, we identified research questions left unexplored across scales, such as the role of animal mobility, as well as the relative contributions of host and vector species to transmission. Importantly, we noted a substantial lack of justification when choosing a functional form for the force of infection. Overall, we showed a great diversity in RVF models, leading to important progress in our comprehension of epidemiological mechanisms. To go further, data gaps must be filled, and modelers need to improve their code accessibility.

Rift Valley Fever Virus Non-Structural Protein S Is Associated with Nuclear Translocation of Active Caspase-3 and Inclusion Body Formation

Rift Valley fever phlebovirus (RVFV) causes Rift Valley fever (RVF), an emerging zoonotic disease that causes abortion storms and high mortality rates in young ruminants as well as severe or even lethal complications in a subset of human patients. This study investigates the pathomechanism of intranuclear inclusion body formation in severe RVF in a mouse model. Liver samples from immunocompetent mice infected with virulent RVFV 35/74, and immunodeficient knockout mice that lack interferon type I receptor expression and were infected with attenuated RVFV MP12 were compared to livers from uninfected controls using histopathology and immunohistochemistry for RVFV nucleoprotein, non-structural protein S (NSs) and pro-apoptotic active caspase-3. Histopathology of the livers showed virus-induced, severe hepatic necrosis in both mouse strains. However, immunohistochemistry and immunofluorescence revealed eosinophilic, comma-shaped, intranuclear inclusions and an intranuclear (co-)localization of RVFV NSs and active caspase-3 only in 35/74-infected immunocompetent mice, but not in MP12-infected immunodeficient mice. These results suggest that intranuclear accumulation of RVFV 35/74 NSs is involved in nuclear translocation of active caspase-3, and that nuclear NSs and active caspase-3 are involved in the formation of the light microscopically visible inclusion bodies.

Intact Type I Interferon Receptor Signaling Prevents Hepatocellular Necrosis but Not Encephalitis in a Dose-Dependent Manner in Rift Valley Fever Virus Infected Mice

Rift Valley fever (RVF) is a zoonotic and emerging disease, caused by the RVF virus (RVFV). In ruminants, it leads to “abortion storms” and enhanced mortality rates in young animals, whereas in humans it can cause symptoms like severe hemorrhagic fever or encephalitis. The role of the innate and adaptive immune response in disease initiation and progression is still poorly defined. The present study used the attenuated RVFV strain clone 13 to investigate viral spread, tissue tropism, and histopathological lesions after intranasal infection in C57BL/6 wild type (WT) and type I interferon (IFN-I) receptor I knockout (IFNAR−/−) mice. In WT mice, 104 PFU RVFV (high dose) resulted in a fatal encephalitis, but no hepatitis 7–11 days post infection (dpi), whereas 103 PFU RVFV (low dose) did not cause clinical disease or significant histopathological lesions in liver and the central nervous system (CNS). In contrast, IFNAR−/− mice infected with 103 PFU RVFV developed hepatocellular necrosis resulting in death at 2–5 dpi and lacked encephalitis. These results show that IFNAR signaling prevents systemic spread of the attenuated RVFV strain clone 13, but not the dissemination to the CNS and subsequent fatal disease. Consequently, neurotropic viruses may be able to evade antiviral IFN-I signaling pathways by using the transneuronal instead of the hematogenous route.

An unusually long Rift valley fever inter-epizootic period in Zambia: Evidence for enzootic virus circulation and risk for disease outbreak

Rift valley fever (RVF) is a mosquito-borne disease of animals and humans. Although RVF outbreaks are usually reported at 5-15-year intervals in sub-Saharan Africa, Zambia has experienced an unusually long inter-epizootic/-epidemic period of more than three decades. However, serological evidence of RVF virus (RVFV) infection in domestic ruminants during this period underscores the need for comprehensive investigation of the mechanisms of virus perpetuation and disease emergence. Mosquitoes (n = 16,778) captured from eight of the ten provinces of Zambia between April 2014 and May 2019 were pooled (n = 961) and screened for RVFV genome by a pan-phlebo RT-PCR assay. Aedes mosquito pools (n = 85) were further screened by nested RT-PCR assay. Sera from sheep (n = 13), goats (n = 259) and wild ungulates (n = 285) were screened for RVFV antibodies by ELISA while genome detection in pooled sera (n = 276) from domestic (n = 248) and wild ungulates (n = 37) was performed by real-time RT-PCR assay. To examine the association between the long inter-epizootic period and climatic variables, we examined El Niño-Southern Oscillation indices, precipitation anomalies, and normalized difference vegetation index. We then derived RVF risk maps by exploring climatic variables that would favor emergence of primary RVFV vectors. While no RVFV genome could be detected in pooled mosquito and serum samples, seroprevalence was significantly high (OR = 8.13, 95% CI [4.63–14.25]) in wild ungulates (33.7%; 96/285) compared to domestic ruminants (5.6%; 16/272). Retrospective analysis of RVF epizootics in Zambia showed a positive correlation between anomalous precipitation (La Niña) and disease emergence. On risk mapping, whilst northern and eastern parts of the country were at high risk, domestic ruminant population density was low (< 21 animals/km²) in these areas compared to low risk areas (>21 animals/km²). Besides evidence of silent circulation of RVFV and the risk of disease emergence in some areas, wildlife may play a role in the maintenance of RVFV in Zambia.

Rift valley fever (RVF) is an important mosquito borne disease of humans and ruminants. RVF is endemic in sub-Saharan Africa where disease outbreaks are frequently reported in humans and animals. For RVF outbreaks to occur, there has to be presence of the host (animals or humans) and favorable climatic conditions that favor emergence of RVF virus vectors (mosquitoes). Understanding this complex interaction enables us to predict future disease outbreaks and map RVF high risk areas. Above normal rainfall and floods will usually trigger RVF outbreaks. In this study, we conducted surveillance for RVF in mosquitoes, domestic and wild ruminants. We then examined climatic conditions that may have been responsible for past RVF outbreaks and the unusually (>30 years) long inter-epizootic period. Finally, we derived RVF risk maps for Zambia using a combination of climatic variables. We found evidence of RVF infection in both wild and domestic ruminants while there was a positive correlation between past RVF outbreaks and above-normal rainfall. On risk mapping, we found favorable conditions (i.e. high rainfall and risk of flooding) for RVF emergence in northern and eastern parts of the country. Studies like this are important in planning surveillance and disease control programs.

NSG-Mice Reveal the Importance of a Functional Innate and Adaptive Immune Response to Overcome RVFV Infection

Rift Valley fever (RVF) is a zoonotic disease caused by RVF Phlebovirus (RVFV). The RVFV MP-12 vaccine strain is known to exhibit residual virulence in the case of a deficient interferon type 1 response. The hypothesis of this study is that virus replication and severity of lesions induced by the MP-12 strain in immunocompromised mice depend on the specific function of the disturbed pathway. Therefore, 10 strains of mice with deficient innate immunity (B6-IFNARtmAgt, C.129S7(B6)-Ifngtm1Ts/J, B6-TLR3tm1Flv, B6-TLR7tm1Aki, NOD/ShiLtJ), helper T-cell- (CD4tm1Mak), cytotoxic T-cell- (CD8atm1Mak), B-cell- (Igh-Jtm1DhuN?+N2), combined T- and B-cell- (NU/J) and combined T-, B-, natural killer (NK) cell- and macrophage-mediated immunity (NOD.Cg-PrkdcscidIl2rgtm1WjI/SzJ (NSG) mice) were subcutaneously infected with RVFV MP-12. B6-IFNARtmAgt mice were the only strain to develop fatal disease due to RVFV-induced severe hepatocellular necrosis and apoptosis. Notably, no clinical disease and only mild multifocal hepatocellular necrosis and apoptosis were observed in NSG mice, while immunohistochemistry detected the RVFV antigen in the liver and the brain. No or low virus expression and no lesions were observed in the other mouse strains. Conclusively, the interferon type 1 response is essential for early control of RVFV replication and disease, whereas functional NK cells, macrophages and lymphocytes are essential for virus clearance.

Genetic Characterization of Rift Valley Fever Virus in Insectivorous Bats, Egypt

Background: The endemic character of Rift Valley fever (RVF) disease points toward an interepidemic reservoir. Although not yet identified, bats and rodents may be implicated in RVF virus (RVFV) epidemiology. In this study, we investigated the putative role of Egyptian frugivorous and insectivorous bats in RVFV epidemiology in Egypt. Methods: From 2019 to 2021, 200 bats of two different species from six Egyptian governorates were tested for phleboviruses using real-time RT-PCR (rRT-PCR) and sequence analysis. Results: Screening through rRT-PCR showed evidence of the RVFV genome only in insectivorous bats. Partial sequence and phylogenetic analysis based on S and M genome segments showed that these viruses are genetically similar to those circulating (clade A) in livestock and humans during previously reported RVFV outbreaks in 1977/78 and 2003 in Egypt. Conclusions: Our molecular data suggest that the bat Pipistrellus deserti could play a role in RVFV ecology in Egypt.

Modelling the persistence and control of Rift Valley fever virus in a spatially heterogeneous landscape

The persistence mechanisms of Rift Valley fever (RVF), a zoonotic arboviral haemorrhagic fever, at both local and broader geographical scales have yet to be fully understood and rigorously quantified. We developed a mathematical metapopulation model describing RVF virus transmission in livestock across the four islands of the Comoros archipelago, accounting for island-specific environments and inter-island animal movements. By fitting our model in a Bayesian framework to 2004-2015 surveillance data, we estimated the importance of environmental drivers and animal movements on disease persistence, and tested the impact of different control scenarios on reducing disease burden throughout the archipelago. Here we report that (i) the archipelago network was able to sustain viral transmission in the absence of explicit disease introduction events after early 2007, (ii) repeated outbreaks during 2004-2020 may have gone under-detected by local surveillance, and (iii) co-ordinated within-island control measures are more effective than between-island animal movement restrictions.

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.

Rift Valley Fever Virus Infection Causes Acute Encephalitis in the Ferret

Rift Valley fever virus (RVFV) is a pathogen of both humans and livestock in Africa and the Middle East. Severe human disease is associated with hepatitis and/or encephalitis. Current pathogenesis studies rely on rodents and nonhuman primates, which have advantages and disadvantages. We evaluated disease progression in Mustela putorius furo (the ferret) following intradermal (i.d.) or intranasal (i.n.) infection. Infected ferrets developed hyperpyrexia, weight loss, lymphopenia, and hypoalbuminemia. Three of four ferrets inoculated intranasally with RVFV developed central nervous system (CNS) disease that manifested as seizure, ataxia, and/or hind limb weakness at 8 to 11 days postinfection (dpi). Animals with clinical CNS disease had transient viral RNAemia, high viral RNA loads in the brain, and histopathological evidence of encephalitis. The ferret model will facilitate our understanding of how RVFV accesses the CNS and has utility for the evaluation of vaccines and/or therapeutics in preventing RVFV CNS disease.IMPORTANCE Animal models of viral disease are very important for understanding how viruses make people sick and for testing out drugs and vaccines to see if they can prevent disease. In this study, we identify the ferret as a model of encephalitis caused by Rift Valley fever virus (RVFV). This novel model will allow researchers to evaluate ways to prevent RVFV encephalitis.

Spatial risk analysis for the introduction and circulation of six arboviruses in the Netherlands

Background

Arboviruses are a growing public health concern in Europe, with both endemic and exotic arboviruses expected to spread further into novel areas in the next decades. Predicting where future outbreaks will occur is a major challenge, particularly for regions where these arboviruses are not endemic. Spatial modelling of ecological risk factors for arbovirus circulation can help identify areas of potential emergence. Moreover, combining hazard maps of different arboviruses may facilitate a cost-efficient, targeted multiplex-surveillance strategy in areas where virus transmission is most likely. Here, we developed predictive hazard maps for the introduction and/or establishment of six arboviruses that were previously prioritized for the Netherlands: West Nile virus, Japanese encephalitis virus, Rift Valley fever virus, tick-borne encephalitis virus, louping-ill virus and Crimean-Congo haemorrhagic fever virus.

Methods

Our spatial model included ecological risk factors that were identified as relevant for these arboviruses by an earlier systematic review, including abiotic conditions, vector abundance, and host availability. We used geographic information system (GIS)-based tools and geostatistical analyses to model spatially continuous datasets on these risk factors to identify regions in the Netherlands with suitable ecological conditions for arbovirus introduction and establishment.

Results

The resulting hazard maps show that there is spatial clustering of areas with either a relatively low or relatively high environmental suitability for arbovirus circulation. Moreover, there was some overlap in high-hazard areas for virus introduction and/or establishment, particularly in the southern part of the country.

Conclusions

The similarities in environmental suitability for some of the arboviruses provide opportunities for targeted sampling of vectors and/or sentinel hosts in these potential hotspots of emergence, thereby increasing the efficient use of limited resources for surveillance.

Identification of Bunyamwera and Possible Other Orthobunyavirus Infections and Disease in Cattle during a Rift Valley Fever Outbreak in Rwanda in 2018

In 2018, a large outbreak of Rift Valley fever (RVF)–like illness in cattle in Rwanda and surrounding countries was reported. From this outbreak, sera samples from 157 cows and 28 goats suspected to be cases of RVF were tested to confirm or determine the etiology of the disease. Specifically, the hypothesis that orthobunyaviruses—Bunyamwera virus (BUNV), Batai virus (BATV), and Ngari virus (NRIV)—were co-circulating and contributed to RVF-like disease was tested. Using reverse transcriptase-polymerase chain reaction (RT-PCR), RVFV RNA was detected in approximately 30% of acutely ill animals, but in all cases of hemorrhagic disease. Seven cows with experienced abortion had positive amplification and visualization by gel electrophoresis of all three segments of either BUNV or BATV, and three of these were suggested to be coinfected with BUNV and BATV. On sequencing, five of these seven cows were conclusively positive for BUNV. However, in several other animals, sequencing was successful for some but not all segments of targeted viruses BUNV and BATV. In addition, there was evidence of RVFV–orthobunyavirus coinfection, through RT-PCR/gel electrophoresis and subsequent Sanger sequencing. In no cases were we able to definitely identify the specific coinfecting viral species. This is the first time evidence for orthobunyavirus circulation has been molecularly confirmed in Rwanda. Furthermore, RT-PCR results suggest that BUNV and BATV may coinfect cattle and that RVFV-infected animals may be coinfected with other orthobunyaviruses. Finally, we confirm that BUNV and, perhaps, other orthobunyaviruses were co-circulating with RVFV and contributed to the burden of disease attributed to RVFV in Rwanda.

Immunogenicity Assessment of Rift Valley Fever Virus Virus-Like Particles in BALB/c Mice

Rift Valley fever (RVF) is an acute, febrile zoonotic disease that is caused by the RVF virus (RVFV) and is spread by arthropod vectors. Virus-like particle (VLP) vaccines, which have the advantages of strong immunogenicity and safety, play an important role in the prevention of this disease. VLPs for RVFV were successfully prepared by our research group using a baculovirus-insect cell expression system. To study the immunogenicity of these RVFV VLPs, a correct 3rd or 4th generation recombinant baculovirus, rBac-N-G, was identified and used to infect Sf9 cells, which were cultured in suspension at a large scale. Subsequently, cell debris was removed by centrifugation, and the VLPs were concentrated by ultracentrifugation and purified using a sucrose gradient, after which they were used to immunize BALB/c mice by intramuscular injection. The results showed that the RVFV VLPs prepared by our research group could effectively induce mice to produce RVFV neutralizing antibodies and that the prepared VLPs could stimulate mouse spleen cells to produce high levels of the cytokines IL-4 and IFN-γ. Moreover, the proportion of lymphocytes producing IL-4 and IFN-γ in the spleen of mice immunized with RVFV VLPs was significantly increased. Therefore, the RVFV VLPs prepared in this study had strong immunogenicity and could effectively activate humoral and cellular immunity in mice. This study lays a solid foundation for the development of RVFV VLP vaccine candidates and promotes the healthy development of animal husbandry and human public health.

The challenging management of Rift Valley Fever in humans: literature review of the clinical disease and algorithm proposal

Rift Valley Fever (RVF) is an emerging zoonotic arbovirus with a complex cycle of transmission that makes difficult the prediction of its expansion. Recent outbreaks outside Africa have led to rediscover the human disease but it remains poorly known. The wide spectrum of acute and delayed manifestations with potential unfavorable outcome much complicate the management of suspected cases and prediction of morbidity and mortality during an outbreak. We reviewed literature data on bio-clinical characteristics and treatments of RVF human illness. We identified gaps in the field and provided a practical algorithm to assist clinicians in the cases assessment, determination of setting of care and prolonged follow-up.

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

Ensuring the successful inactivation of select agent material is critical for maintaining compliance with federal regulations and safeguarding laboratory personnel from exposure to dangerous pathogens. Rift Valley fever virus (RVFV), naturally transmitted by mosquitoes, is classified as a select agent by the CDC and USDA due to its potential to cause significant economic losses to the livestock industry and its demonstrated potential to emerge into naïve geographic areas. Herein we describe several effective inactivation procedures for RVFV infected mosquito samples. We also demonstrate the vaccine strain MP-12 can be used as an appropriate analog for inactivation testing and describe a method of validating inactivation using Amicon filters. Briefly, we show the following inactivation methods are all effective at inactivating RVFV and MP-12 by following the manufacturers'/established protocols: 4 % paraformaldehyde, Trizol LS (ThermoFisher Scientific), MagMAX™-96 Viral RNA Isolation Kit (ThermoFisher Scientific), and Mag-Bind® Viral DNA/RNA 96 Kit (Omega Bio-Tek).

Genetically Modified Rabies Virus Vector-Based Rift Valley Fever Virus Vaccine is Safe and Induces Efficacious Immune Responses in Mice

Rift Valley fever virus (RVFV), which causes Rift Valley fever (RVF), is a mosquito-borne zoonotic pathogen that causes serious morbidity and mortality in livestock and humans. RVF is a World Health Organization (WHO) priority disease and, together with rabies, is a major health burden in Africa. Here, we present the development and characterization of an inactivated recombinant RVFV and rabies virus (RABV) vaccine candidate (rSRV9-eGn). Immunization with rSRV9-eGn stimulated the production of RVFV-specific IgG antibodies and induced humoral and cellular immunity in mice but did not induce the production of neutralizing antibodies. IgG1 and IgG2a were the main isotypes observed by IgG subtype detection, and IgG3 antibodies were not detected. The ratios of IgG1/IgG2a > 1 indicated a Type 2 humoral immune response. An effective vaccine is intended to establish a long-lived population of memory T cells, and mice generated memory cells among the proliferating T cell population after immunization with rSRV9-eGn, with effector memory T cells (T_EM) as the major population. Due to the lack of prophylactic treatment experiments, it is impossible to predict whether this vaccine can protect animals from RVFV infection with only high titres of anti-RVFV IgG antibodies and no neutralizing antibodies induced, and thus, protection confirmation needs further verification. However, this RVFV vaccine designed with RABV as the vector provides ideas for the development of vaccines that prevent RVFV and RABV infections.

Evaluation of an Indirect Enzyme-Linked Immunosorbent Assay Based on Recombinant Baculovirus-Expressed Rift Valley Fever Virus Nucleoprotein as the Diagnostic Antigen

The increasing risk of Rift Valley fever virus (RVFV) infection as a global veterinary and public health threat demands the development of safe and accurate diagnostic tests. The aim of this study was to assess the suitability of a baculovirus expression system to produce recombinant RVFV nucleoprotein (N) for use as serodiagnostic antigen in an indirect enzyme-linked immunosorbent assay (ELISA). The ability of the recombinant N antigen to detect RVFV antibody responses was evaluated in ELISA format using antisera from sheep and cattle experimentally infected with two genetically distinct wild-type RVFV strains and sera from indigenous sheep and goat populations exposed to natural RVFV field infection in The Gambia. The recombinant N exhibited specific reactivity with the N-specific monoclonal antibody and various hyperimmune serum samples from ruminants. The indirect ELISA detected N-specific antibody responses in animals with 100% sensitivity compared to the plaque reduction neutralization test (6 to 21 days postinfection) and with 97% and 100% specificity in sheep and cattle, respectively. There was a high level of correlation between the indirect N ELISA and the virus neutralization test for sheep sera (R ² = 0.75; 95% confidence interval [CI] = 0.73 to 0.92) and cattle sera (R ² = 0.80; 95% CI = 0.67 to 0.97); in addition, the N-specific ELISA detected RVFV seroprevalence levels of 26.1% and 54.3% in indigenous sheep and goats, respectively, in The Gambia. The high specificity and correlation with the virus neutralization test support the idea of the feasibility of using the recombinant baculovirus-expressed RVFV N-based indirect ELISA to assess RVFV seroprevalence in livestock in areas of endemicity and nonendemicity.

Plant extracts for developing mosquito larvicides: From laboratory to the field, with insights on the modes of action

In the last decades, major research efforts have been done to investigate the insecticidal activity of plant-based products against mosquitoes. This is a modern and timely challenge in parasitology, aimed to reduce the frequent overuse of synthetic pesticides boosting resistance development in mosquitoes and causing serious threats to human health and environment. This review covers the huge amount of literature available on plant extracts tested as mosquito larvicides, particularly aqueous and alcoholic ones, due to their easy formulation in water without using surfactants. We analysed results obtained on more than 400 plant species, outlining that 29 of them have outstanding larvicidal activity (i.e., LC₅₀ values below 10 ppm) against major vectors belonging to the genera Anopheles, Aedes and Culex, among others. Furthermore, synergistic and antagonistic effects between plant extracts and conventional pesticides, as well as among selected plant extracts are discussed. The efficacy of pure compounds isolated from the most effective plant extracts and - when available - their mechanism of action, as well as the impact on non-target species, is also covered. These belong to the following class of secondary metabolites: alkaloids, alkamides, sesquiterpenes, triterpenes, sterols, flavonoids, coumarins, anthraquinones, xanthones, acetogenonins and aliphatics. Their mode of action on mosquito larvae ranges from neurotoxic effects to inhibition of detoxificant enzymes and larval development and/or midugut damages. In the final section, current drawbacks as well as key challenges for future research, including technologies to synergize efficacy and improve stability - thus field performances - of the selected plant extracts, are outlined. Unfortunately, despite the huge amount of laboratory evidences about their efficacy, only a limited number of studies was aimed to validate their efficacy in the field, nor the epidemiological impact potentially arising from these vector control operations has been assessed. This strongly limits the development of commercial mosquito larvicides of botanical origin, at variance with plant-borne products developed in the latest decades to kill or repel other key arthropod species of medical and veterinary importance (e.g., ticks and lice), as well as mosquito adults. Further research on these issues is urgently needed.

The influence of raw milk exposures on Rift Valley fever virus transmission

Rift Valley fever virus (RVFV) is a zoonotic phlebovirus that can be transmitted to humans or livestock by mosquitoes or through direct contact with contaminated bodily fluids and tissues. Exposure to bodily fluids and tissues varies by types of behaviors engaged for occupational tasks, homestead responsibilities, or use in dietary or therapeutic capacities. While previous studies have included milk exposures in their analyses, their primary focus on livestock exposures has been on animal handling, breeding, and slaughter. We analyzed data from multiple field surveys in Kenya with the aim of associating RVFV infection to raw milk exposures from common animal species. Of those with evidence of prior RVFV infection by serology (n = 267), 77.2% engaged in milking livestock compared to 32.0% for 3,956 co-local seronegative individuals (p < 0.001), and 86.5% of seropositive individuals consumed raw milk compared to 33.4% seronegative individuals (p < 0.001). Individuals who milked and also consumed raw milk had greater odds of RVFV exposure than individuals whose only contact to raw milk was through milking. Increased risks were associated with exposure to milk sourced from cows (p < 0.001), sheep (p < 0.001), and goats (p < 0.001), but not camels (p = 0.98 for consuming, p = 0.21 for milking). Our data suggest that exposure to raw milk may contribute to a significant number of cases of RVFV, especially during outbreaks and in endemic areas, and that some animal species may be associated with a higher risk for RVFV exposure. Livestock trade is regulated to limit RVFV spread from endemic areas, yet further interventions designed to fully understand the risk of RVFV exposure from raw milk are imperative.

Identification and evaluation of antivirals for Rift Valley fever virus

Rift Valley fever virus (RVFV) is the causative agent of Rift Valley fever (RVF) that affects both livestock and humans. There are neither fully licensed RVF vaccines available for human or animal use, nor effective antiviral drugs approved for human use in the U.S. To identify antiviral compounds effective for RVF, we developed and employed a cell-based high-throughput assay using a recombinant RVFV MP-12 strain, which expresses Renilla luciferase in place of the NSs protein, to screen 727 small compounds purchased from the National Institutes of Health. Twenty-three compounds were initially identified using the screening assay. Two compounds, 6-azauridine and mitoxantrone, also inhibited the replication of the parental MP-12 strain encoding the NSs gene, with limited cytotoxic effects. The respective 50% inhibitory concentrations were 29.07 μM and 79.85 μM when tested with the parental MP-12 strain at a multiplicity of infection of 2. The compounds were further evaluated using the STAT-1 KO mouse model. At one hour post intranasal inoculation of MP-12 strain, mice were intranasally treated with each indicated compound twice daily. Mice treated with either placebo or 6-azauridine displayed severe weight loss and reached the threshold for euthanasia with obvious neurologic symptoms. Onset of disease was, however, delayed in mice treated with either ribavirin or mitoxantrone. The results indicated that mitoxantrone can reduce the severity of diseases in RVFV-infected mice. Our studies build the foundation for the initial screening and efficacy studies of RVF antivirals in a BSL-2 environment, avoiding the higher risks of BSL-3 exposure with wild-type virus.

The Ecological Significance and Implications of Transovarial Transmission among the Vector-Borne Bunyaviruses: A Review

Transovarial transmission (TOT) is a widespread and efficient process through which pathogens can be passed between generations of arthropod vectors. Many species within the order Bunyavirales utilize TOT as a means of persisting within the environment when classical horizontal transmission is not possible due to ecological constraints. The purpose of this review is to summarize previous findings regarding the ecological significance of TOT among viruses in the order Bunyavirales and identify the gaps in knowledge regarding this important mechanism of arboviral maintenance.

Management of arthropod vector data - Social and ecological dynamics facing the One Health perspective

Emerging infectious diseases (EIDs) are spread by direct and/or indirect contacts between a pathogen or parasite and their hosts. Arthropod vectors have evolved as excellent bloodsuckers, providing an elegant transportation mode for a wide number of infectious agents. The nature of pathogen and parasite transfer and the models used to predict how a disease might spread are magnified in complexity when an arthropod vector is part of the disease cycle. One Health is a worldwide strategy for expanding interdisciplinary collaborations and communications in all aspects of health care for humans, animals and the environment. It would benefit from a structured analysis to address vectoring of arthropod-borne diseases as a dynamic transactional process. This review focused on how arthropod vector data can be used to better model and predict zoonotic disease outbreaks. With enhanced knowledge to describe arthropod vector disease transfer, researchers will have a better understanding about how to model disease outbreaks. As public health research evolves to include more social-ecological systems, the roles of society, ecology, epidemiology, pathogen/parasite evolution and animal behavior can be better captured in the research design. Overall, because of more collaborative data collection processes on arthropod vectors, disease modeling can better predict conditions where EIDs will occur.

Interspecific network centrality, host range and early-life development are associated with wildlife hosts of Rift Valley fever virus

Rift Valley fever virus (RVFV) is responsible for a substantive disease burden in pastoralist communities and the agricultural sector in the African continent and Arabian Peninsula. Enzootic, epizootic and zoonotic RVFV transmission dynamics remain ill-defined, particularly due to a poor understanding of the role of mammalian hosts in the epidemiology and infection ecology of this arbovirus. Using a piecewise structural equation model, this study sought to identify associations between biological and ecological characteristics of mammalian species and documented RVFV infection to highlight species-level traits that may influence wildlife host status. Interspecific network centrality, size of species home range and reproductive life-history traits were all associated with being an RVFV host. The identification of these species-level characteristics may help to provide ecological context for the role of wildlife amplification hosts in the epidemiology of spillover to livestock and humans and may also help to identify specific points of vulnerability at the wildlife-livestock interface.

A Review of Bunyamwera, Batai, and Ngari Viruses: Understudied Orthobunyaviruses With Potential One Health Implications

Bunyamwera (BUNV), Batai (BATV), and Ngari (NRIV) are mosquito-borne viruses of the Bunyamwera serogroup in the Orthobunyavirus genus of the Bunyaviridae family. These three viruses have been found to cause disease in both livestock animals, avian species, and humans. Thus, these viruses pose a potential threat to human public health, animal health, and food security. This is especially the case in the developing nations, where BUNV and NRIV are found, mainly in Africa. BUNV and BATV are fairly well characterized, while NRIV is not well characterized owing to only sporadic detection in human and animal populations in Africa. Reassortment is common among bunyaviruses, but NRIV is believed to be the only natural reassortant of the Bunyamwera serogroup. It resulted from a combination of BUNV S and L segments and the BATV M segment. This indicates at least some level co-circulation of BUNV and BATV, which have no historically been reported to overlap in geographic distributions. But as these viruses are undercharacterized, there remains a gap in the understanding of how such reassortment could occur, and the consequences of such. Due to their combined wide range of hosts and vectors, geographic distributions, potential severity of associated diseases, and potential for transmissibility between vertebrate hosts, these viruses represent a significant gap in knowledge with important One Health implications. The goal of this review is to report available knowledge of and identify potential future directions for study of these viruses. As these are collectively understudied viruses, there is a relative paucity of data; however, we use available studies to discuss different perspectives in an effort to promote a better understanding of these three viruses and the public and One Health threat(s) they may pose.

Overlapping CD8+ and CD4+ T-cell epitopes identification for the progression of epitope-based peptide vaccine from nucleocapsid and glycoprotein of emerging Rift Valley fever virus using immunoinformatics approach

Rift Valley fever virus (RVFV) is an emergent arthropod-borne zoonotic infectious viral pathogen which causes fatal diseases in the humans and ruminants. Currently, no effective and licensed vaccine is available for the prevention of RVFV infection in endemic as well as in non-endemic regions. So, an immunoinformatics-driven genome-wide screening approach was performed for the identification of overlapping CD8+ and CD4+ T-cell epitopes and also linear B-cell epitopes from the conserved sequences of the nucleocapsid (N) and glycoprotein (G) of RVFV. We identified overlapping 99.39% conserved 1 CD8+ T-cell epitope (MMHPSFAGM) from N protein and 100% conserved 7 epitopes (AVFALAPVV, LAVFALAPV, FALAPVVFA, VFALAPVVF, IAMTVLPAL, FFDWFSGLM, and FLLIYLGRT) from G protein and also identified IL-4 and IFN-γ induced (99.39% conserved) 1 N protein CD4+ T-cell epitope (HMMHPSFAGMVDPSL) and 100% conserved 5 G protein CD4+ T-cell epitopes (LPALAVFALAPVVFA, PALAVFALAPVVFAE, GIAMTVLPALAVFAL, GSWNFFDWFSGLMSW, and FFLLIYLGRTGLSKM). The overlapping CD8+ and CD4+ T-cell epitopes were bound with most conserved HLA-C*12:03 and HLA-DRB1*01:01, respectively with the high binding affinity (kcal/mol). The combined population coverage analysis revealed that the allele frequencies of these epitopes are high in endemic and non-endemic regions. Besides, we found 100% conserved and non-allergenic 2 decamer B-cell epitopes, GVCEVGVQAL and RVFNCIDWVH of G protein had the sequence similarity with the nonamer CD8+ T-cell epitopes, VCEVGVQAL and RVFNCIDWV, respectively. Consequently, these epitopes may be used for the development of epitope-based peptide vaccine against emerging RVFV. However, in vivo and in vitro experiments are required for their efficient use as a vaccine.

Wetlands, wild Bovidae species richness and sheep density delineate risk of Rift Valley fever outbreaks in the African continent and Arabian Peninsula

Rift Valley fever (RVF) is an emerging, vector-borne viral zoonosis that has significantly impacted public health, livestock health and production, and food security over the last three decades across large regions of the African continent and the Arabian Peninsula. The potential for expansion of RVF outbreaks within and beyond the range of previous occurrence is unknown. Despite many large national and international epidemics, the landscape epidemiology of RVF remains obscure, particularly with respect to the ecological roles of wildlife reservoirs and surface water features. The current investigation modeled RVF risk throughout Africa and the Arabian Peninsula as a function of a suite of biotic and abiotic landscape features using machine learning methods. Intermittent wetland, wild Bovidae species richness and sheep density were associated with increased landscape suitability to RVF outbreaks. These results suggest the role of wildlife hosts and distinct hydrogeographic landscapes in RVF virus circulation and subsequent outbreaks may be underestimated. These results await validation by studies employing a deeper, field-based interrogation of potential wildlife hosts within high risk taxa.

Rift Valley fever (RVF) is a vector-borne zoonotic disease that imparts a substantial burden to the economy and public health of pastoralist communities across the African continent and Arabian Peninsula. Furthermore, RVF is also an emerging pathogen of growing global concern. Knowledge of the epidemiological and ecological factors that influence the geographic distribution of RVF outbreaks and determine risk for humans and animals is incomplete. The current study examined the distribution of RVF outbreaks from 1998 to 2016 and modeled their occurrence as a function of climate, surface water, land cover, livestock density, wild mammalian species richness, and human migration. The results indicate that wetlands, Bovidae species richness, and sheep density were associated with increased risk of RVF outbreaks. Our findings contribute to improved understanding of the spatial and ecological dynamics of RVF risk with a particular emphasis on the distribution of wetlands and potential wildlife reservoirs in designing RVF surveillance programs.

Absence of Evidence of Rift Valley Fever Infection in Eulemur fulvus (Brown Lemur) in Mayotte During an Interepidemic Period

The potential role of Eulemur fulvus (brown lemur) in the epidemiology of Rift Valley fever (RVF) in Mayotte, during an interepidemic period, was explored. In February and March 2016, 72 animals were blood sampled and tested for RVF. No evidence of RVF genome or antibodies was found in the samples. The role of other wild mammals on the island should, however, be further investigated.

Quantifying the potential pathways and locations of Rift Valley fever virus entry into the United States

The global invasion of West Nile virus, chikungunya virus and Zika virus in the past two decades suggests an increasing rate of mosquito-borne virus (arbovirus) dispersal. Rift Valley fever virus (RVFV) is an arbovirus identified as a high-consequence threat to the United States (USA) because of the severe economic and health consequences associated with disease. Numerous studies demonstrate that the USA is receptive to RVFV transmission based on the widespread presence of competent mosquito species and vertebrate species. In this study, the potential pathways and locations of RVFV entry into the USA were quantitatively estimated to support a priori surveillance and RVFV prevention strategies. International movement data, ecological data and epidemiological data were combined to estimate the number of RVFV-infected mosquitoes entering the USA. Results suggest infected humans travelling by plane pose the highest risk of importing RVFV into the USA, followed by the unintentional transport of infected adult mosquitoes by ship and airplane. Furthermore, New York, New York, Washington DC, Atlanta, Georgia, and Houston, Texas, are implicated as the most likely regions of RVFV entry. Results are interpreted and discussed to support the prediction and mitigation of RVFV spread to the USA.

Global research trends of World Health Organization's top eight emerging pathogens

BACKGROUND

On December 8th, 2015, World Health Organization published a priority list of eight pathogens expected to cause severe outbreaks in the near future. To better understand global research trends and characteristics of publications on these emerging pathogens, we carried out this bibliometric study hoping to contribute to global awareness and preparedness toward this topic.

METHOD

Scopus database was searched for the following pathogens/infectious diseases: Ebola, Marburg, Lassa, Rift valley, Crimean-Congo, Nipah, Middle Eastern Respiratory Syndrome (MERS), and Severe Respiratory Acute Syndrome (SARS). Retrieved articles were analyzed to obtain standard bibliometric indicators.

RESULTS

A total of 8619 journal articles were retrieved. Authors from 154 different countries contributed to publishing these articles. Two peaks of publications, an early one for SARS and a late one for Ebola, were observed. Retrieved articles received a total of 221,606 citations with a mean ± standard deviation of 25.7 ± 65.4 citations per article and an h-index of 173. International collaboration was as high as 86.9%. The Centers for Disease Control and Prevention had the highest share (344; 5.0%) followed by the University of Hong Kong with 305 (4.5%). The top leading journal was Journal of Virology with 572 (6.6%) articles while Feldmann, Heinz R. was the most productive researcher with 197 (2.3%) articles. China ranked first on SARS, Turkey ranked first on Crimean-Congo fever, while the United States of America ranked first on the remaining six diseases. Of retrieved articles, 472 (5.5%) were on vaccine - related research with Ebola vaccine being most studied.

CONCLUSION

Number of publications on studied pathogens showed sudden dramatic rise in the past two decades representing severe global outbreaks. Contribution of a large number of different countries and the relatively high h-index are indicative of how international collaboration can create common health agenda among distant different countries.

Broad-Range Antiviral Activity of Hydrogen Sulfide Against Highly Pathogenic RNA Viruses

Hydrogen sulfide is an important endogenous mediator that has been the focus of intense investigation in the past few years, leading to the discovery of its role in vasoactive, cytoprotective and anti-inflammatory responses. Recently, we made a critical observation that H₂S also has a protective role in paramyxovirus infection by modulating inflammatory responses and viral replication. In this study we tested the antiviral and anti-inflammatory activity of the H₂S slow-releasing donor GYY4137 on enveloped RNA viruses from Ortho-, Filo-, Flavi- and Bunyavirus families, for which there is no FDA-approved vaccine or therapeutic available, with the exception of influenza. We found that GYY4137 significantly reduced replication of all tested viruses. In a model of influenza infection, GYY4137 treatment was associated with decreased expression of viral proteins and mRNA, suggesting inhibition of an early step of replication. The antiviral activity coincided with the decrease of viral-induced pro-inflammatory mediators and viral-induced nuclear translocation of transcription factors from Nuclear Factor (NF)-kB and Interferon Regulatory Factor families. In conclusion, increasing cellular H₂S is associated with significant antiviral activity against a broad range of emerging enveloped RNA viruses, and should be further explored as potential therapeutic approach in relevant preclinical models of viral infections.