Widening geographic range of Rift Valley fever disease clusters associated with climate change in East Africa

Bridging knowledge gaps in phytotherapy for a neglected zoonotic disease: Rift valley fever

This study sought to review the current state of phytotherapy and natural compound research against Rift Valley fever (RVF), a neglected zoonotic disease exacerbated by climate change and globalisation. A comprehensive literature search was conducted in Scopus, PubMed, and Cochrane Database of Systematic Reviews up to February 2025. Studies focusing on phytotherapy or natural compounds for RVF were included and analysed for research trends, geographical distribution, and compounds. Sixteen studies met the inclusion criteria. Studies focused on antiviral activity (12/16, 75 %; %95CI, 51-90) and vaccine development (4/16, 25 %; %95CI, 10-50). Plants from the Fabaceae family (7/26, 27 %; 95 %CI, 14-46) and polyphenols (45/94, 48 %; 95 %CI, 38-58) were most frequently investigated. No clinical studies were identified. There are major knowledge gaps in the clinical application of phytotherapy for RVF and limited research contributions from endemic African nations. The identified natural compounds in this work could provide a foundation for future research.

PROJECTING CLIMATE CHANGE IMPACTS ON INTER-EPIDEMIC RISK OF RIFT VALLEY FEVER ACROSS EAST AFRICA

Background

Rift Valley fever (RVF) is a zoonotic disease that causes sporadic, multi-country epidemics. However, RVF virus (RVFV) also circulates during inter-epidemic periods. There is limited understanding of how climate change will affect inter-epidemic RVF. Here, we project inter-epidemic RVF risk under future climate scenarios, focusing on the East African countries of Kenya, Tanzania, and Uganda.

Methods

We combined data on inter-epidemic RVF outbreaks and spatially-explicit predictor variables to build a predictive model of inter-epidemic RVF risk. We validated our model using RVFV serological data from humans. We then projected inter-epidemic RVF risk for three future time periods (2021-2040, 2041-2060, 2061-208) under three climate scenarios (SSP126, SSP245, SSP370). Finally, we combined risk projections with human population projections to estimate the future population at risk of inter-epidemic RVF across the study region.

Findings

Our model showed seasonality in inter-epidemic RVF, with risk peaking May-July following the long rains (March-May). Projections for future climate scenarios suggested that disease risk will increase January-March, with the present-day hotspots of east Kenya, southeast Tanzania, and southwest Uganda remaining high-risk. By 2061-2080, > 117 million people in the study region may be at risk from inter-epidemic RVF, a fourfold increase relative to the historical (1970-2000) estimate of ~25 million people.

Interpretation

Climate change will shift the inter-epidemic RVF risk landscape, with increasing short rains (October-December) driving increased risk January-March. Mitigating the future health impacts of RVF will require increased disease surveillance, prevention, and control effort in risk hotspots.

Funding

US National Institutes of Health.

Atypical hyperendemicity of Rift Valley fever in Southwestern Uganda associated with the rapidly evolving lineage C viruses

Introduction

Recent Rift Valley fever (RVF) epidemiology in eastern Africa region is characterized by widening geographic range and increasing frequency of small disease clusters. Here we conducted studies in southwestern (SW) Uganda region that has since 2016 reported increasing RVF activities.

Methods

A 22-month long hospital-based study in three districts of SW Uganda targeting patients with acute febrile illness (AFI) or unexplained bleeding was followed by a cross-sectional population-based human-animal survey. We then estimated RVFV force of infection (FOI) and yearly cases using the age-structured seroprevalence data and conducted genomic phylodynamic modelling of RVFV isolates.

Results

Overall RVF prevalence was 10.5% (205 of 1,968) among febrile or hemorrhagic cases, including 5% with acute (PCR or IgM positive) infection, averaging 5 cases per month. Community-based serosurvey recorded prevalence of 11.8% (88 of 743) among humans and 14.6% (347 of 2,383) in livestock. Expected yearly human RVF cases were 314-2,111 per 1,369 km 2 in SW Uganda versus 0-711 in comparable regions of Kenya and Tanzania. Viral genomic studies identified RVFV lineage C, sub-clade C.2.2, as the circulating strain in SW Uganda since 2019. Lineage C strain has undergone recent rapid evolution and clonal expansion resulting in four sub-clades, C.1.1, C.1.2, C.2.1, and C.2.2, that are more adept at establishing endemicity in new territories.

Conclusions

We demonstrate an atypical RVF hyperendemic region in SW Uganda characterized by sustained human clinical RVF cases, unusually high population prevalence, and high number of expected yearly human cases, associated in part with emergence of new RVFV sub-lineages.

Key points

Rift Valley fever (RVF) studies in SW Uganda found atypical sustained human cases averaging 5 cases/month, >10% population prevalence, and expected yearly cases >3-fold higher (314-2,111 vs 0-711) than comparable regions in East Africa, associated with emerging RVFV sub-lineages.

Therapeutic development to accelerate malaria control through intentional intervention layering

The clinical development of novel vaccines, injectable therapeutics, and oral chemoprevention drugs has the potential to deliver significant advancements in the prevention of Plasmodium falciparum malaria. These innovations could support regions in accelerating malaria control, transforming existing intervention packages by supplementing interventions with imperfect effectiveness or offering an entirely new tool. However, to layer new medical tools as part of an existing programme, malaria researchers must come to an agreement on the gaps that currently limit the effectiveness of medical interventions for moderate to low transmission settings. In this perspective, three crucial gaps that may prevent new therapeutics from being used to their fullest extent are presented. First, do burden reduction outcomes, which are typically monitored in studies of new medical products, sufficiently capture the broader goal of accelerating malaria control? Layering novel malaria products requires monitoring health outcomes that reflect the novel product's targeted stage of the parasite life cycle, in addition to all-infection and prevalence-based outcomes. Second, what public health outcome does a novel medical prevention tool provide that existing malaria interventions cannot fully deliver? Novel medical tools should be developed not just for an incremental improvement in preventive efficacy over an existing product, but also to meet a gap in protection. Specifically, this means designing products with components that target parts of the parasite life cycle beyond the scope of existing therapeutics, and better addressing populations and settings not well covered by existing tools. Finally, when do the population-level benefits of a multi-tool prevention programme justify the individual-level outcomes from receiving multiple interventions? An individual-level perspective should be key for exploring when and how layering a novel prevention intervention can accelerate efforts towards P. falciparum malaria control.

Serological Evidence of Cryptic Rift Valley Fever Virus Transmission Among Humans and Livestock in Central Highlands of Kenya

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.

Have you heard of Rift Valley fever? Findings from a multi-country study in East and Central Africa

Introduction

Rift Valley Fever (RVF) has caused outbreaks in Africa, impacting human health and animal trade. Recently, sporadic detections among humans and animals in East Africa have replaced large-scale outbreaks. We assessed RVF knowledge levels in East and Central Africa across countries with different epidemiological profiles.

Materials and Methods

Individuals aged ≥10 years with acute febrile illness were enrolled from six health facilities in Kenya, Uganda, and the Democratic Republic of Congo (DRC). Sociodemographic information was collected and participants asked questions on RVF transmission, symptoms, prevention, and control. Blood samples were tested for anti-RVF antibodies (IgG and IgM). Knowledge was categorized as absent, basic, or advanced. Descriptive and ordinal logistic regression analysis identified factors associated with RVF knowledge.

Results

Among 4,806 participants (median age 31, IQR 22-44, 57.5% female), only 20.5% demonstrated any RVF knowledge (16.4% basic, 4.1% advanced). Knowledge levels varied by country: DRC (3.1%), Uganda (16.1%), and Kenya (42.6%). Factors associated with RVF knowledge included age 20-40 years aOR 1.72 (95%CI 1,24-2.22) and >40 years 2.42 (95%CI 1.74-3.420), male gender aOR 1.54 (95%CI 1.31-1.82), healthcare workers aOR 7.95 (95%CI 5.25-12.1), residence in Kenya aOR 23.5 (95%CI 15.8-35.8) or Uganda 5.4 (95%CI 3.68-8.38), completing primary education aOR 3.24 (95%CI 1.94-5.75) with advanced education shown to increase knowledge, postgraduate aOR 11.5 (95%CI 4.0-32.4). Other factors included presence of livestock within the homes aOR 1.30 (95%CI 1.06-1.59) and prevention of mosquito bites aOR 1.55 (95%CI 0.46-0.66). Animal farmers, butchers, and those with close animal contact showed no association, despite being at-risk populations.

Conclusion

RVF knowledge was low overall, varying by country, age, education, and environmental factors. Increased awareness is crucial for high-exposure groups in all regions, particularly in Uganda, where exposure is higher, but knowledge remains low.