Estimation of Rift Valley fever virus spillover to humans during the Mayotte 2018-2019 epidemic

AbstractRift Valley fever (RVF) is an emerging, zoonotic, arboviral haemorrhagic fever threatening livestock and humans mainly in Africa. RVF is of global concern, having expanded its geographical range over the last decades. The impact of control measures on epidemic dynamics using empirical data has not been assessed. Here, we combined seroprevalence livestock and human RVF case data from the 2018-2019 epidemic in Mayotte, with a dynamic mathematical model. Using a Bayesian inference framework, we estimated viral transmission potential amongst livestock, and spillover from livestock to humans, through both direct contact and vector-mediated routes. Model simulations were used to assess the impact of vaccination on reducing the human epidemic size. Reactive vaccination immunising 20% of the livestock population reduced the number of human cases by 30%. To achieve a similar impact, delaying the vaccination by one month required using 50% more vaccine doses, and vaccinating only humans required 20 times as more as the number of doses for livestock. Finally, with 53.92% (95%CrI [44.76-61.29]) of livestock estimated to be immune at the end of the epidemic wave, viral re-emergence in the next rainy season (2019-2020) was unlikely. We present the first mathematical model for RVF fitted to real-world data to estimate virus transmission parameters, and able to inform potential control programmes. Human and animal health surveillance, and timely livestock vaccination appear to be key in reducing disease risk in humans. We furthermore demonstrate the value of a One Health quantitative approach to surveillance and control of zoonotic infectious diseases.

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Estimation of Rift Valley fever virus spillover to humans during the Mayotte 2018–2019 epidemic

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2004468117 ◽

2020 ◽

Vol 117 (39) ◽

pp. 24567-24574 ◽

Cited By ~ 1

Author(s):

Raphaëlle Métras ◽

W. John Edmunds ◽

Chouanibou Youssouffi ◽

Laure Dommergues ◽

Guillaume Fournié ◽

...

Keyword(s):

Rift Valley ◽

Direct Contact ◽

Rift Valley Fever ◽

Rift Valley Fever Virus ◽

Animal Health ◽

Hemorrhagic Fever ◽

Control Measures ◽

Similar Reduction ◽

Valley Fever ◽

The Impact

Rift Valley fever (RVF) is an emerging, zoonotic, arboviral hemorrhagic fever threatening livestock and humans mainly in Africa. RVF is of global concern, having expanded its geographical range over the last decades. The impact of control measures on epidemic dynamics using empirical data has not been assessed. Here, we fitted a mathematical model to seroprevalence livestock and human RVF case data from the 2018–2019 epidemic in Mayotte to estimate viral transmission among livestock, and spillover from livestock to humans through both direct contact and vector-mediated routes. Model simulations were used to assess the impact of vaccination on reducing the epidemic size. The rate of spillover by direct contact was about twice as high as vector transmission. Assuming 30% of the population were farmers, each transmission route contributed to 45% and 55% of the number of human infections, respectively. Reactive vaccination immunizing 20% of the livestock population reduced the number of human cases by 30%. Vaccinating 1 mo later required using 50% more vaccine doses for a similar reduction. Vaccinating only farmers required 10 times as more vaccine doses for a similar reduction in human cases. Finally, with 52.0% (95% credible interval [CrI] [42.9–59.4]) of livestock immune at the end of the epidemic wave, viral reemergence in the next rainy season (2019–2020) is unlikely. Coordinated human and animal health surveillance, and timely livestock vaccination appear to be key to controlling RVF in this setting. We furthermore demonstrate the value of a One Health quantitative approach to surveillance and control of zoonotic infectious diseases.

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Drivers of Rift Valley fever virus persistence and the impact of control measures in a spatially heterogeneous landscape: the case of the Comoros archipelago, 2004–2015

10.1101/2021.03.10.434721 ◽

2021 ◽

Author(s):

Warren S. D. Tennant ◽

Eric Cardinale ◽

Catherine Cêtre-Sossah ◽

Youssouf Moutroifi ◽

Gilles Le Godais ◽

...

Keyword(s):

Rift Valley ◽

Rift Valley Fever ◽

Rift Valley Fever Virus ◽

Virus Transmission ◽

Control Measures ◽

Virus Persistence ◽

Valley Fever ◽

Grande Comore ◽

The Many ◽

The Impact

AbstractRift Valley fever (RVF) is one of the many zoonotic arboviral haemorrhagic fevers present in Africa. The ability of the pathogen to persist in multiple geographically distinct regions has raised concerns about its potential for spread to and persistence within currently disease-free areas. However, the mechanisms for which RVF virus persistence occurs at both local and broader geographical scales have yet to be fully understood and rigorously quantified. Here, we developed a mathematical metapopulation model describing RVF virus transmission in livestock across the four islands of the Comoros archipelago and fitted this model in a Bayesian framework to surveillance data conducted in livestock across those islands between 2004 and 2015. In doing so, we estimated the importance of island-specific environmental factors and animal movements between those islands on the persistence of RVF virus in the archipelago, and we further tested the impact of different control scenarios on reducing disease burden. We demonstrated that the archipelago network was able to sustain viral transmission over 10 years after assuming only one introduction event during early 2007. Movement restrictions were only useful to control the disease in Anjouan and Mayotte, as Grande Comore and Mohéli were able to self-sustain RVF viral persistence, probably due to local environmental conditions that are more favourable for vectors. We also evidenced that repeated outbreaks during 2004-2020 may have gone under-detected by local surveillance in Grande Comore and Mohéli. Strengthened longterm and coordinated surveillance would enable the detection of viral re-emergence and evaluation of different relevant vaccination programmes.

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

Nature Communications ◽

10.1038/s41467-021-25833-8 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Warren S. D. Tennant ◽

Eric Cardinale ◽

Catherine Cêtre-Sossah ◽

Youssouf Moutroifi ◽

Gilles Le Godais ◽

...

Keyword(s):

Rift Valley ◽

Rift Valley Fever ◽

Animal Movement ◽

Rift Valley Fever Virus ◽

Virus Transmission ◽

Control Measures ◽

Environmental Drivers ◽

Animal Movements ◽

Valley Fever ◽

The Impact

AbstractThe 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.

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Diversity and Abundance of Potential Vectors of Rift Valley Fever Virus in the North Region of Cameroon

Insects ◽

10.3390/insects11110814 ◽

2020 ◽

Vol 11 (11) ◽

pp. 814

Author(s):

Poueme Namegni Rodrigue Simonet ◽

Njan-Nloga Alexandre Michel ◽

Wade Abel ◽

Eisenbarth Albert ◽

Groschup Martin Hermann ◽

...

Keyword(s):

Rift Valley ◽

Rift Valley Fever ◽

Rift Valley Fever Virus ◽

Fever Virus ◽

Control Measures ◽

Sub Saharan Africa ◽

Effective Control ◽

P Value ◽

Valley Fever ◽

The North

Rift Valley fever (RVF) is a major viral zoonosis transmitted by mosquitoes. The virus is endemic in most parts of sub-Saharan Africa and can affect humans, livestock, and wild ungulates. Knowledge of the biology of vectors of Rift Valley fever virus (RVFV) is essential for the establishment of effective control measures of the disease. The objective of this study was to determine the species diversity and relative abundance of potential RVFV vectors in the North Region of Cameroon. Adult mosquitoes were trapped during the wet and dry seasons from December 2017 to January 2019 with “EVS Light” traps with CO2 baits placed at selected sites. The captured mosquitoes were identified using dichotomous keys according to standard procedures. The abundance was calculated with regard to site, zone, and collection season. A total of 27,851 mosquitoes belonging to four genera (Aedes, Anopheles, Mansonia, and Culex) and comprising 31 species were caught (including 22 secondary vectors (98.05%) and nine primary vectors (1.94%). The total number of mosquitoes varied significantly depending on the locality (p-value < 0.001). The average number of mosquitoes collected per trap night was significantly higher in irrigated areas (p-value < 0.001), compared to urban and non-irrigated areas. The study revealed the presence of potential primary and secondary vectors of RVFV with varying abundance and diversity according to locality and ecological site in the North Region of Cameroon. The results showed that the genus Mansonia with the species Ma. uniformis and Ma. africana formed the dominant taxon (52.33%), followed by the genera Culex (45.04%) and Anopheles (2.61%). The need for molecular analysis (PCR) tests for RVFV RNA research and viral isolation methods on these vectors to determine their role in the epidemiology and control of RVF cannot be overemphasized.

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Rift Valley fever virus: future emergence and the impact on One Health

The Biochemist ◽

10.1042/bio03903022 ◽

2017 ◽

Vol 39 (3) ◽

pp. 22-25

Author(s):

Elysse N. Grossi-Soyster ◽

A. Desiree LaBeaud

Keyword(s):

Rift Valley ◽

Global Economy ◽

Rift Valley Fever ◽

Rift Valley Fever Virus ◽

Wide Spectrum ◽

Fever Virus ◽

Valley Fever ◽

Animal Populations ◽

Agricultural Industries ◽

The Impact

Rift Valley fever virus (RVFV) is a mosquito-borne Bunyavirus that currently affects livestock and humans, causing a wide spectrum of symptoms. RVFV was confined to the African continent for many decades and spread to the Arabian Peninsula in recent history. The potential for widespread emergence into new regions and populations is possible and likely, as many outbreaks are driven by human behaviour and livestock trade. While many imported human cases have been detected, establishment of the virus in new geographic areas will depend on amplification in dense animal populations. Western and European countries have identified a substantial risk for the emergence of RVFV, as agricultural industries constitute a large percentage of the global economy.

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It’s risky to wander in September: modelling the epidemic potential of Rift Valley fever in a Sahelian setting

10.1101/2020.02.25.20027821 ◽

2020 ◽

Author(s):

Hélène Cecilia ◽

Raphaëlle Métras ◽

Assane Gueye Fall ◽

Modou Moustapha Lo ◽

Renaud Lancelot ◽

...

Keyword(s):

At Risk ◽

Rift Valley ◽

Rift Valley Fever ◽

Rift Valley Fever Virus ◽

Small Ruminants ◽

Time Interval ◽

List Type ◽

Temperature Dependent ◽

Valley Fever ◽

The Impact

AbstractEstimating the epidemic potential of vector-borne diseases, along with the relative contribution of underlying mechanisms, is crucial for animal and human health worldwide. In West African Sahel, several outbreaks of Rift Valley fever (RVF) have occurred over the last decades, but uncertainty remains about the conditions necessary to trigger these outbreaks. We use the basic reproduction number (R0) as a measure of RVF epidemic potential in Northern Senegal, and map its value in two distinct ecosystems, namely the Ferlo and the Senegal river delta and valley. We consider three consecutive rainy seasons (July-November 2014, 2015 and 2016) and account for several vector and animal species. Namely, we parametrize our model with estimates of Aedes vexans arabiensis, Culex poicilipes, Culex tritaeniorhynchus, cattle, sheep and goats abundances. The impact of RVF virus introduction is assessed every week, in 4367 pixels of 3,5km2. The results of our analysis indicate that September was the month with highest epidemic potential in each study area, while at-risk locations varied between seasons. We show that decreased vector densities do not highly reduce R0 and that cattle immunity has a greater impact on reducing transmission than small ruminants immunity. The host preferences of vectors and the temperature-dependent time interval between their blood meals are crucial parameters needing further biological investigations.HighlightsSeptember is a period of high Rift Valley fever epidemic potential in northern Senegal regardless of the year, but exact locations where epidemics might start change between rainy seasons.Decreased vector densities during the rainy season did not highly reduce the epidemic potential of at-risk locations.High levels of immunity in cattle populations reduce more Rift Valley fever virus transmission than a high immunity in small ruminants in our study area. This aspect should be investigated further for targeted vaccination campaigns.Precise estimates of vector feeding preferences and the temperature-dependent lenght of their gonotrophic cycle are key to ensure a good detection of at-risk pixels.

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Coupling an Agent-Based Model with a Mathematical Model of Rift Valley Fever for Studying the Impact of Animal Migrations on the Rift Valley Fever Transmission

Computational Science and Its Applications – ICCSA 2020 - Lecture Notes in Computer Science ◽

10.1007/978-3-030-58802-1_34 ◽

2020 ◽

pp. 471-485

Author(s):

Paul Python Ndekou Tandong ◽

Papa Ibrahima Ndiaye ◽

Alassane Bah ◽

Dethie Dione ◽

Jacques André Ndione

Keyword(s):

Mathematical Model ◽

Rift Valley ◽

Rift Valley Fever ◽

Agent Based Model ◽

Valley Fever ◽

Agent Based ◽

The Impact

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

10.1101/2021.09.29.21264307 ◽

2021 ◽

Author(s):

Keli N Gerken ◽

A. Desiree LaBeaud ◽

Henshaw Mandi ◽

Maïna L’Azou Jackson ◽

J. Gabrielle Breugelmans ◽

...

Keyword(s):

Indian Ocean ◽

Rift Valley ◽

Rift Valley Fever ◽

Survey Design ◽

Rift Valley Fever Virus ◽

Fever Virus ◽

Valley Fever ◽

Populations At Risk ◽

The Indian Ocean ◽

The Impact

Background: Rift Valley fever virus (RVFV) is a lethal threat to humans and livestock in many parts of Africa, Arabia, 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) insect 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 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.

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