Search

Rift Valley fever virus (RVFV) is an arthropod-borne phlebovirus reported to be circulating in most parts of Africa. Since 2009, RVFV has been suspected of continuously circulating in the Union of Comoros. To estimate the incidence of RVFV antibody acquisition in the Comorian ruminant population, 191 young goats and cattle were selected in six distinct zones and sampled periodically from April 2010 to August 2011. We found an estimated incidence of RVFV antibody acquisition of 17.5% (95% confidence interval (CI): [8.9–26.1]) with a significant difference between islands (8.2% in Grande Comore, 72.3% in Moheli and 5.8% in Anjouan). Simultaneously, a longitudinal entomological survey was conducted and ruminant trade-related information was collected. No RVFV RNA was detected out of the 1,568 blood-sucking caught insects, including three potential vectors of RVFV mosquito species. Our trade survey suggests that there is a continuous flow of live animals from eastern Africa to the Union of Comoros and movements of ruminants between the three Comoro islands. Finally, a cross-sectional study was performed in August 2011 at the end of the follow-up. We found an estimated RVFV antibody prevalence of 19.3% (95% CI: [15.6%–23.0%]). Our findings suggest a complex RVFV epidemiological cycle in the Union of Comoros with probable inter-islands differences in RVFV circulation patterns. Moheli, and potentially Anjouan, appear to be acting as endemic reservoir of infection whereas RVFV persistence in Grande Comore could be correlated with trade in live animals with the eastern coast of Africa. More data are needed to estimate the real impact of the disease on human health and on the national economy. Author Summary: Rift Valley fever (RVF) is a viral disease transmitted by mosquitoes to ruminants. The disease may affect humans and has a great impact on the economy of the affected country. RVF occurs mostly in African countries, but epidemics have been reported in Madagascar and in the Arabian Peninsula. In the Union of Comoros, RVF virus (RVFV) has been suspected of continuously circulating since 2009 without any notifications of the typical clinical signs by the Comorian Animal Health Services. From April 2010 to August 2011, we conducted a livestock longitudinal survey in Grande Comore, Moheli and Anjouan. Our study aimed to detect RVFV-specific antibody acquisitions in cattle and goats. Simultaneously, a longitudinal entomological survey was conducted to describe the diversity of mosquitoes in the study zones and ruminant trade-related information was collected. Our investigations showed that Comoros ruminants acquired RVFV-specific antibodies all along the year and particularly in Moheli during the dry season. Our findings suggest a complex RVFV epidemiological cycle in the Union of Comoros with probable inter-islands differences in RVFV circulation patterns. The disease appears to be endemic in Moheli and potentially Anjouan, but the persistence of the disease in Grande Comore could be correlated with trade in live animals with the eastern coast of Africa. [ABSTRACT FROM AUTHOR]

As further confirmation of a first human case of Rift Valley fever in 2007 in Comoros, we isolated Rift Valley fever virus in suspected human cases. These viruses are genetically closely linked to the 2006-2007 isolates from Kenya. [ABSTRACT FROM AUTHOR]

Rift Valley fever (RVF) recently re-emerged in Mayotte. We described, for the first time, that the mosquito species Eretmapodites subsimplicipes, a highly abundant species in Mayotte, is a competent vector for the transmission of RVF virus using three distinct populations native to Mayotte. We also showed that Aedes albopictus specimens are able to transmit RVF virus (RVFV) as previously observed in mosquito populations of other countries emphasizing the need of the increase vigilance for this highly invasive species of global distribution. Altogether, these results underline the epidemiological importance of both species for RVFV transmission in Mayotte and contribute to better understand the RVF epidemiological cycle and help to implement efficient prevention measures., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

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., (© 2021. The Author(s).)

Rift Valley fever (RVF) is a vector-borne viral disease of major animal and public health importance. In 2018-19, it caused an epidemic in both livestock and human populations of the island of Mayotte. Using Bayesian modelling approaches, we assessed the spatio-temporal pattern of RVF virus (RVFV) infection in livestock and human populations across the island, and factors shaping it. First, we assessed if (i) livestock movements, (ii) spatial proximity from communes with infected animals, and (iii) livestock density were associated with the temporal sequence of RVFV introduction into Mayotte communes' livestock populations. Second, we assessed whether the rate of human infection was associated with (a) spatial proximity from and (b) livestock density of communes with infected animals. Our analyses showed that the temporal sequence of RVFV introduction into communes' livestock populations was associated with livestock movements and spatial proximity from communes with infected animals, with livestock movements being associated with the best model fit. Moreover, the pattern of human cases was associated with their spatial proximity from communes with infected animals, with the risk of human infection sharply increasing if livestock in the same or close communes were infected. This study highlights the importance of understanding livestock movement networks in informing the design of risk-based RVF surveillance programs., Competing Interests: The authors have declared that no competing interests exist.

A cross-sectional study was conducted to explore the epidemiological situation in Mayotte regarding two orbiviruses: Bluetongue virus (BTV) and Epizootic Haemorrhagic Disease virus (EHDV). In all, 385 individual asymptomatic cattle were blood-sampled (one EDTA and one serum tube per animal) between February and June 2016. Antibody (ELISA) and genome prevalence (PCR) was assessed. Almost all the selected cattle showed antibodies against both BTV and EHDV, at 99.5% (CI95% [98.00, 100]) and 96.9% (CI95% [94.5, 98.3]), respectively. Most of the cattle acquired antibodies in their first years of age. EHDV and BTV genomes were detected in 25.2% (CI95% [21.1, 29.8]) and 18.2% (CI95% [14.6, 22.4]) of samples, respectively. Coinfection with BTV and EHDV was observed in 9.4% of samples (CI95% [6.8, 12.7]). Cattle under three years old were more frequently reported as positive for genome detection by PCR than older cattle. Five serotypes of BTV and one serotype of EHDV were identified from eight samples: BTV-4, BTV-9, BTV-11, BTV-15, BTV-19 and EHDV-6, of which some were reported in neighbouring areas. BTV and EHDV both circulate in Mayotte and in its surrounding territories., (Copyright © 2018 Elsevier B.V. All rights reserved.)

In recent years, Madagascar and the Comoros archipelago have been affected by epidemics of Rift Valley fever (RVF), however detection of Rift Valley fever virus (RVFV) in zebu, sheep and goats during the post epidemic periods was frequently unsuccessful. Thus, a highly sensitive real-time RT-PCR assay was developed for the detection of RVFV at low viral loads. A new RVF SYBR Green RT-PCR targeting the M segment was tested on serum from different RVF seronegative ruminant species collected from May 2010 to August 2011 in Madagascar and the Comoros archipelago and compared with a RVF specific quantitative real time RT-PCR technique, which is considered as the reference technique. The specificity was tested on a wide range of arboviruses or other viruses giving RVF similar clinical signs. A total of 38 out of 2756 serum samples tested positive with the new RT-PCR, whereas the reference technique only detected 5 out of the 2756. The described RT-PCR is an efficient diagnostic tool for the investigation of enzootic circulation of the RVF virus. It allows the detection of low viral RNA loads adapted for the investigations of reservoirs or specific epidemiological situations such as inter-epizootic periods., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Rift Valley fever threatens human and animal health. After a human case was confirmed in Comoros in 2007, 4 serosurveys among ruminants in Mayotte suggested that Rift Valley fever virus had been circulating at low levels since 2004, although no clinical cases occurred in animals. Entomologic and ecologic studies will help determine outbreak potential.