Paving the way for human vaccination against Rift Valley fever virus: A systematic literature review of RVFV epidemiology from 1999 to 2021

Abstract

Background Rift Valley fever virus (RVFV) is a lethal threat to humans and livestock in many parts of Africa, the Arabian Peninsula, and the Indian Ocean. This systematic review’s objective was to consolidate understanding of RVFV epidemiology during 1999–2021 and highlight knowledge gaps relevant to plans for human vaccine trials. Methodology/Principal findings The review is registered with PROSPERO (CRD42020221622). Reports of RVFV infection or exposure among humans, animals, and/or vectors in Africa, the Arabian Peninsula, and the Indian Ocean during the period January 1999 to June 2021 were eligible for inclusion. Online databases were searched for publications, and supplemental materials were recovered from official reports and research colleagues. Exposures were classified into five groups: 1) acute human RVF cases, 2) acute animal cases, 3) human RVFV sero-surveys, 4) animal sero-surveys, and 5) arthropod infections. Human risk factors, circulating RVFV lineages, and surveillance methods were also tabulated. In meta-analysis of risks, summary odds ratios were computed using random-effects modeling. 1104 unique human or animal RVFV transmission events were reported in 39 countries during 1999–2021. Outbreaks among humans or animals occurred at rates of 5.8/year and 12.4/year, respectively, with Mauritania, Madagascar, Kenya, South Africa, and Sudan having the most human outbreak years. Men had greater odds of RVFV infection than women, and animal contact, butchering, milking, and handling aborted material were significantly associated with greater odds of exposure. Animal infection risk was linked to location, proximity to water, and exposure to other herds or wildlife. RVFV was detected in a variety of mosquito vectors during interepidemic periods, confirming ongoing transmission. Conclusions/Significance With broad variability in surveillance, case finding, survey design, and RVFV case confirmation, combined with uncertainty about populations-at-risk, there were inconsistent results from location to location. However, it was evident that RVFV transmission is expanding its range and frequency. Gaps assessment indicated the need to harmonize human and animal surveillance and improve diagnostics and genotyping. Given the frequency of RVFV outbreaks, human vaccination has strong potential to mitigate the impact of this now widely endemic disease.

Urban risk factors for human Rift Valley fever virus exposure in Kenya

“…The current lack of RVFV risk assessments in urban areas of endemic counties puts a significant portion of the population at risk and undermines preventive measures for worldwide RVFV emergence and control. RVFV outbreaks are becoming more sporadic from year-to-year and previously low risk areas of endemic countries are experiencing human outbreaks without any evidence of prior livestock infections which supports a potential low-level circulation of RVFV in livestock [24].…”

Determining the acceptability of a novel One Health vaccine for Rift Valley Fever prior to phase II/III clinical trials in Uganda

“…[ 6 ] However, the magnitude of zoonotic transmission cannot be clearly defined due to very low and unreliable human and livestock surveillance for the disease, and poor collective knowledge on how farmers recognise and manage the acute symptoms of RVF. [ 7 , 8 ] This is concerning, as early detection of RVF is crucial to containing an outbreak, when preventative technologies such as vaccines have not yet provided an adequate solution. [ 9 ]…”

Evaluations of rationally designed rift valley fever vaccine candidate RVax-1 in mosquito and rodent models

“…Rift Valley fever (RVF) is a mosquito-borne zoonotic viral disease endemic to sub-Saharan Africa, Egypt, Madagascar, the Comoros, Saudi Arabia, and Yemen, which is caused by the Rift Valley fever virus (RVFV: genus Phlebovirus , family Phenuiviridae ) 1 – 3 . In nature, RVFV is spread via vertical viral transmission in floodwater Aedes mosquitoes, and horizontal viral transmission among various species of mosquitoes and susceptible animals.…”