Search Results (149)

Rift Valley fever (RVF) is a zoonotic disease caused by the Rift Valley fever virus (RVFV), affecting humans, livestock, and wild ruminants. This study aimed to characterize and assess the genetic diversity of RVFV strains circulating among livestock in Uganda. Blood samples were collected between January 2021 and May 2024 from apparently healthy cattle, goats, and sheep in four districts. The samples were first screened for RVFV antibodies using ELISA; antibody-positive samples were subsequently tested for viral RNA using reverse transcriptase quantitative PCR (RT-qPCR). The PCR-positive samples underwent targeted amplicon sequencing, and phylogenetic analyses of the small (S) and large (L) genome segments were conducted to determine viral lineages. Of the 833 ELISA-positive samples, 10 (all from cattle) tested positive for RVFV RNA using RT-qPCR. Consensus sequences were successfully generated for six S segments and one L genome segment. A phylogenetic analysis revealed that all sequences belonged to lineage C, showing close genetic similarity to RVFV strains previously identified in Uganda, Kenya, Sudan, Madagascar, and Saudi Arabia. Limited genetic diversity was observed at both the nucleotide and amino acid levels. The detection of RVFV in apparently healthy cattle suggests ongoing, low-level viral circulation in Uganda. These findings offer important insights for guiding RVF surveillance, control, and policymaking in the country. Full article

In Africa, Rift Valley Fever poses a substantial risk to animal health, and human cases occur after contact with infected animals or their tissues. RVF has re-emerged in Uganda after nearly five decades, with multiple outbreaks recorded since 2016. We investigated a unique RVF outbreak associated with an animal abortion storm of 30 events and human cases on a dairy farm in Mbarara District, Western Uganda, in February 2023. Genomic analysis was performed, comparing animal and human RVF viruses (RVFV) circulating in the region. A cluster of thirteen human RVF cases and nine PCR-positive animals could directly be linked with the abortion storm. Overall, during the year 2023, we confirmed 61 human RVFV cases across Uganda, 88.5% of which were reported to have had direct contact with livestock, and a high case fatality rate of 31%. We recommend implementing extensive health education programs in affected communities and using sustainable mosquito control strategies to limit transmission in livestock, coupled with initiating animal vaccination trials in Uganda. Full article

Black flies (Diptera: Simuliidae) are important vectors of pathogens, including filarial nematodes, protozoans, and arboviruses, which significantly impact human and animal health. Although their role in arbovirus transmission has not been as thoroughly studied as that of mosquitoes and ticks, advances in molecular tools, particularly metagenomics, have enabled the identification of non-cultivable viruses, significantly enhancing our understanding of black-fly-borne viral diversity and their public and veterinary health implications. However, these methods can also detect insect-specific viruses (i.e., viruses that are unable to replicate in vertebrate hosts), which may lead to the incorrect classification of black flies as potential vectors. This underscores the need for further research into their ecological and epidemiological roles. This systematic review, conducted following the PRISMA protocol, compiled and analyzed evidence on arbovirus detection in Simuliidae from scientific databases. Several arboviruses were identified in these insects, including vesicular stomatitis virus New Jersey serotype (VSVNJ), Venezuelan equine encephalitis virus (VEEV), and Rift Valley fever virus. Additionally, in vitro studies evaluating the vector competence of Simuliidae for arboviruses such as dengue virus, Murray Valley encephalitis virus, and Sindbis virus were reviewed. These findings provide critical insights into the potential role of black flies in arbovirus transmission cycles, emphasizing their importance as vectors in both public and veterinary health contexts. Full article

Rift Valley fever virus (RVFV) is a mosquito-transmitted bunyavirus that can cause substantial morbidity and mortality in livestock and humans, for which there are no currently available licensed human therapeutics or vaccines. Therefore, the development of safe and effective antivirals is both necessary and urgent. The Gc protein is the primary target of the neutralizing antibody response related to Rift Valley fever virus. Here, we report one Gc-specific neutralizing antibody (NA137) isolated from an alpaca and one bispecific antibody (E2-NA137), the protective efficacies of which we evaluated in A129 mice. In this prophylactic study, the survival rates of the NA137 and E2-NA137 groups were both 80%, and in the treatment study, the survival rates were 20% and 60%, respectively. Altogether, our results emphasize that NA137 and E2-NA137 provide a potential approach for treating RVFV either prophylactically or therapeutically. Full article

Insect-borne viruses may account for a significant proportion of non-malaria and non-bacterial febrile illnesses in Liberia. Although the presence of many arthropod vectors has been documented, the collective burden of arbovirus infections and baseline pre-existing immunity remains enigmatic. Our goal was to determine the seroprevalence of arbovirus exposure across the country using a resource-sparing, multiplex immunoassay to determine IgG responses to immunodominant antigens. 532 human serum samples, from healthy adults, collected from 10 counties across Liberia, were measured for IgG reactivity against antigens of eight common flavi-, alpha-, and orthobunya/nairoviruses suspected to be present in West Africa. Approximately 32.5% of our samples were reactive to alphavirus (CHIKV) E2, ~7% were reactive separately to West Nile (WNV) and Zika virus (ZIKV) NS1, while 4.3 and 3.2% were reactive to Rift Valley Fever virus (RVFV) N and Dengue virus-2 (DENV-2) NS1, respectively. Altogether, 21.6% of our samples were reactive to ≥1 flavivirus NS1s. Of the CHIKV E2 reactive samples, 8.5% were also reactive to at least one flavivirus NS1, and six samples were concurrently reactive to antigens of all three arbovirus groups, suggesting a high burden of multiple arbovirus infections for some participants. These insights suggest the presence of these four arbovirus families in Liberia with low and moderate rates of flavi- and alphavirus infections, respectively, in healthy adults. Further confirmational investigation, such as mosquito surveillance or other serological tests, is warranted and should be conducted before initiating additional flavivirus vaccination campaigns. The findings of these studies can help guide healthcare resource mobilization, vector control, and animal husbandry practices. Full article

Rift Valley fever (RVF) is a vector-borne zoonotic viral disease that causes abortion storms, fetal malformations, and neonatal mortality in livestock ruminants. In humans, RVF can lead to hemorrhagic fever, encephalitis, retinitis, or blindness, and about 1% of patients die. Since there are no registered vaccines for human use, developing RVF vaccines for use in animals is crucial to protect animals and prevent the spread of the virus from infecting humans. We recently developed a live bovine herpesvirus type 1 quadruple gene-mutant vector (BoHV-1qmv) that lacks virulence and immunosuppressive properties. Further, we engineered a BoHV-1qmv-vectored subunit Rift Valley fever virus (RVFV) vaccine (BoHV-1qmv Sub-RVFV) for cattle, in which a chimeric polyprotein coding for the RVFV Gc, Gn, and bovine granulocyte–macrophage colony-stimulating factor (GMCSF) proteins is fused but cleaved proteolytically in infected cells into individual membrane-anchored Gc and secreted Gn-GMCSF proteins. Calves vaccinated with the BoHV-1qmv Sub-RVFV vaccine generated moderate levels of RVFV-specific serum-neutralizing (SN) antibodies and cellular immune responses. In the current study, we repurposed the BoHV-1qmv Sub-RVFV for sheep by replacing the RVFV Gc and Gn ORF sequences codon-optimized for bovines with the corresponding ovine-codon-optimized sequences and by fusing the sheep GM-CSF ORF sequences with the Gn ORF sequence. A combined primary intranasal-plus-subcutaneous primary immunization induced a moderate level of BoHV-1 (vector)- and vaccine strain MP12-specific SN antibodies and MP-12-specific cellular immune responses. Notably, an intranasal booster vaccination after 29 days triggered a rapid (within 7 days) rise in MP-12-specific SN antibody titers. Therefore, the BoHV-1qmv-vectored subunit RVFV vaccine is safe and highly immunogenic in sheep and can potentially be an efficient subunit vaccine for sheep against RVFV. Full article

Background: Rift Valley fever virus (RVFV) is a zoonotic virus that poses a significant threat to both livestock and human health and has caused outbreaks in endemic regions. In humans, most patients experience a febrile illness; however, in some patients, RVF disease may result in hemorrhagic fever, retinitis, or encephalitis. While several veterinary vaccines are being utilized in endemic countries, currently, there are no licensed RVF vaccines or therapeutics for human use. Neutralizing antibodies specifically targeting vulnerable pathogen epitopes are promising candidates for prophylactic and therapeutic interventions. In the case of RVFV, the surface glycoproteins Gc and Gn, which harbor neutralizing epitopes, represent the primary targets for vaccine and neutralizing antibody development. Methods: We report the implementation of advanced 10x Genomics technology, enabling high-throughput single-cell analysis for the identification of rare and potent antibodies against RVFV. Following the immunization of mice with live attenuated rMP-12-GFP virus and successive Gc/Gn boosts, memory B cell populations (both general and antigen-specific) were sorted from splenocytes by flow cytometry. Deep sequencing of the antibody repertoire at a single-cell resolution, together with bioinformatic analyses, was applied for BCR pair selection based on their abundance and specificity. Results: Twenty-three recombinant monoclonal antibodies (mAbs) were selected and expressed, and their antigen-binding capacities were characterized. About half of them demonstrated specific binding to their cognate antigen with relatively high binding affinities. Conclusions: These antibodies could be used for the future development of efficacious therapeutics, as well as for studying virus-neutralizing mechanisms. The current study, in which the single-cell sequencing approach was implemented for the development of antibodies targeting the RVFV surface proteins Gc and Gn, demonstrates the effective applicability of this technique for antibody discovery purposes. Full article

Rift Valley fever virus (RVFV) is a mosquito-borne zoonotic disease within the genus Phlebovirus. Symptoms of the disease in animals range from moderate to severe febrile illness, which significantly impacts the livestock industry and causes severe health complications in humans. Similar to bunyaviruses in the genus Orthobunyavirus transmitted by mosquitoes, RVFV progression is dependent on the susceptibility of the physical, cellular, microbial, and immune response barriers of the vectors. These barriers, shaped by the genetic makeup of the mosquito species and the surrounding environmental temperature, exert strong selective pressure on the virus, affecting its replication, evolution, and spread. The changing climate coupled with the aforementioned bottlenecks are significant drivers of RVF epidemics and expansion into previously nonendemic areas. Despite the link between microclimatic changes and RVF outbreaks, there is still a dearth of knowledge on how these temperature effects impact RVF transmission and vector competence and virus persistence during interepidemic years. This intricate interdependence between the virus, larval habitat temperatures, and vector competence necessitates increased efforts in addressing RVFV disease burden. This review highlights recent advancements made in response to shifting demographics, weather patterns, and conveyance of RVFV. Additionally, ongoing studies related to temperature-sensitive variations in RVFV–vector interactions and knowledge gaps are discussed. Full article

The Rift Valley fever virus (RVFV) causes haemorrhagic fever, encephalitis, and permanent blindness and has been listed by the WHO as a priority pathogen. To study RVFV pathogenesis and identify small-molecule antivirals, we established a novel In Vivo model using zebrafish larvae. Pericardial injection of RVFV resulted in ~4 log₁₀ viral RNA copies/larva, which was inhibited by the antiviral 2′-fluoro-2′-deoxycytidine. The optical transparency of the larvae allowed detection of RVFV_eGFP in the liver and sensory nervous system, including the optic tectum and retina, but not the brain or spinal cord. Thus, RVFV-induced blindness likely occurs due to direct damage to the eye and peripheral neurons, rather than the brain. Treatment with the JAK-inhibitor ruxolitinib, as well as knockout of stat1a but not stat1b, enhanced RVFV replication to ~6 log₁₀ viral RNA copies/larva and ultra-bright livers, although without dissemination to sensory neurons or the eye, thereby confirming the critical role of stat1 in RVFV pathogenesis. Full article

Rift Valley fever phlebovirus (RVFV) is a zoonotic mosquito-borne pathogen endemic to sub-Saharan Africa and the Arabian Peninsula which causes Rift Valley fever in ruminant livestock and humans. Co-infection with divergent viral strains can produce reassortment among the L, S, and M segments of the RVFV genome. Reassortment events can produce novel genotypes with altered virulence, transmission dynamics, and/or mosquito host range. This can have severe implications in areas where RVFV is endemic and convolutes our ability to anticipate transmission and circulation in novel geographic regions. Previously, we evaluated the frequency of RVFV reassortment in a susceptible ruminant host and observed low rates of reassortment (0–1.7%). Here, we tested the hypothesis that reassortment occurs predominantly in the mosquito using a highly permissive vector, Culex tarsalis. Cells derived from Cx. tarsalis or adult mosquitoes were co-infected with either two virulent (Kenya-128B-15 and SA01-1322) or a virulent and attenuated (Kenya-128B-15 and MP-12) strain of RVFV. Our results showed approximately 2% of virus genotypes isolated from co-infected Cx. tarsalis-derived cells were reassortant. Co-infected mosquitoes infected via infectious bloodmeal resulted in a higher percentage of reassortant virus (2–60%) isolated from midgut and salivary tissues at 14 days post-infection. The percentage of reassortant genotypes isolated from the midguts of mosquitoes co-infected with Kenya-128B-15 and SA01-1322 was similar to that of mosquitoes co-infected with Kenya-128B-15 and MP-12- strains (60 vs. 47%). However, only 2% of virus isolated from the salivary glands of Kenya-128B-15 and SA01-1322 co-infected mosquitoes represented reassortant genotypes. This was contrasted by 54% reassortment in the salivary glands of mosquitoes co-infected with Kenya-128B-15 and MP-12 strains. Furthermore, we observed preferential inclusion of genomic segments from the three parental strains among the reassorted viruses. Replication curves of select reassorted genotypes were significantly higher in Vero cells but not in Culex—derived cells. These data imply that mosquitoes play a crucial role in the reassortment of RVFV and potentially contribute to driving evolution of the virus. Full article

Rift Valley fever virus (RVFV) is an emerging mosquito-borne arbovirus of One Health importance that caused two large outbreaks in Rwanda in 2018 and 2022. Information on vector species with a role in RVFV eco-epidemiology in Rwanda is scarce. Here we sought to identify potential mosquito vectors of RVFV in Rwanda, their distribution and abundance, as well as their infection status. Since an outbreak of RVF occurred during the study period, data were obtained both during an interepidemic period and during the 2022 Rwanda RVF outbreak. Five districts of the eastern province of Rwanda were prospected using a combination of unbaited light traps and Biogents (BG Sentinel and Pro) traps baited with an artificial human scent during three periods, namely mid-August to mid-September 2021, December 2021, and April to May 2022. Trapped mosquitoes were morphologically identified and tested for viral evidence using both RT-PCR and virus isolation methods on a Vero cell line. A total of 14,815 adult mosquitoes belonging to five genera and at least 17 species were collected and tested as 765 monospecific pools. Culex quinquefasciatus was the most predominant species representing 72.7% of total counts. Of 527 mosquito pools collected before the 2022 outbreak, a single pool of Cx. quinquefasciatus showed evidence of RVFV RNA. Of 238 pools collected during the outbreak, RVFV was detected molecularly from five pools (two pools of Cx. quinquefasciatus, two pools of Anopheles ziemanni, and one pool of Anopheles gambiae sensu lato), and RVFV was isolated from the two pools of Cx. quinquefasciatus, from Kayonza and Rwamagana districts, respectively. Minimum infection rates (per 1000 mosquitoes) of 0.4 before the outbreak and 0.6–7 during the outbreak were noted. Maximum-likelihood phylogenetic analysis indicates that RVFV detected in these mosquitoes is closely related to viral strains that circulated in livestock in Rwanda and in Burundi during the same RVF outbreak in 2022. The findings reveal initial evidence for the incrimination of several mosquito species in the transmission of RVFV in Rwanda and highlight the need for more studies to understand the role of each species in supporting the spread and persistence of RVFV in the country. Full article

Although the highlands of East Africa lack the geo-ecological landmarks of Rift Valley fever (RVF) disease hotspots to participate in cyclic RVF epidemics, they have recently reported growing numbers of small RVF clusters. Here, we investigated whether RVF cycling occurred among livestock and humans in the central highlands of Kenya during inter-epidemic periods. A 2-year prospective hospital-based study among febrile patients (March 2022–February 2024) in Murang’a County of Kenya was followed by a cross-sectional human–animal survey. A total of 1468 febrile patients were enrolled at two clinics and sera tested for RVF virus RNA and antiviral antibodies. In the cross-sectional study, humans (n = 282) and livestock (n = 706) from randomly selected households were tested and questionnaire data were used to investigate sociodemographic and environmental risk factors by multivariate logistic regression. No human (n = 1750) or livestock (n = 706) sera tested positive for RVFV RNA. However, 4.4% livestock and 2.0% humans tested positive for anti-RVFV IgG, including 0.27% febrile patients who showed four-fold IgG increase and 2.4% young livestock (<12 months old), indicating recent virus exposure. Among humans, the odds of RVF exposure increased significantly (p < 0.05, 95% CI) in males (aOR: 4.77, 2.08–12.4), those consuming raw milk (aOR: 5.24, 1.13–17.9), milkers (aOR: 2.69, 1.23–6.36), and participants residing near quarries (aOR: 2.4, 1.08–5.72). In livestock, sheep and goats were less likely to be seropositive (aOR: 0.27, 0.12–0.60) than cattle. The increase in RVF disease activities in the highlands represents a widening geographic dispersal of the virus, and a greater risk of more widespread RVF epidemics in the future. Full article

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. Full article

Rift Valley fever (RVF) is a mosquito-borne viral disease that primarily affects animals, especially ruminants, but has the capacity to infect humans and result in outbreaks. Infection with the causative agent, RVF virus (RVFV), causes severe disease in domestic animals, especially sheep, resulting in fever, anorexia, immobility, abortion, and high morbidity and mortality rates in neonate animals. Humans become infected through exposure to infected animals and, less frequently, directly via a mosquito bite. A greater awareness of RVFV and its epidemic potential has resulted in increased investment in the development of interventions, especially vaccines. There is currently no substitute for the use of animal models in order to evaluate these vaccines. As outbreaks of RVF disease are difficult to predict or model, conducting Phase III clinical trials will likely not be feasible. Therefore, representative animal model systems are essential for establishing efficacy data to support licensure. Nonhuman primate (NHP) species are often chosen due to their closeness to humans, reflecting similar susceptibility and disease kinetics. This review covers the use of NHP models in RVFV research, with much of the work having been conducted in rhesus macaques and common marmosets. The future direction of RVF work conducted in NHP is discussed in anticipation of the importance of it being a key element in the development and approval of a human vaccine. Full article

Rift Valley fever (RVF) is a mosquito-borne viral zoonosis that causes high fetal and neonatal mortality rates in ruminants and sometimes severe to fatal complications like encephalitis and hemorrhagic fever in humans. There is no licensed RVF vaccine for human use while approved livestock vaccines have suboptimal safety or efficacy. We designed self-amplifying RNA (saRNA) RVF vaccines and assessed their humoral immunogenicity in mice. Plasmid DNA encoding the Rift Valley fever virus (RVFV) medium (M) segment consensus sequence (WT consensus) and its derivatives mutated to enhance cell membrane expression of the viral surface glycoproteins n (Gn) and c (Gc) were assessed for in vitro expression. The WT consensus and best-expressing derivative (furin-T2A) were cloned into a Venezuelan equine encephalitis virus (VEEV) plasmid DNA replicon and in vitro transcribed into saRNA. The saRNA was formulated in lipid nanoparticles and its humoral immunogenicity in BALB/c mice was assessed. High quantities of dose-dependent RVFV Gn IgG antibodies were detected in the serum of all mice immunized with either WT consensus or furin-T2A saRNA RVF vaccines. Significant RVFV pseudovirus-neutralizing activity was induced in mice immunized with 1 µg or 10 µg of the WT consensus saRNA vaccine. The WT consensus saRNA RVF vaccine warrants further development. Full article