Identification of drivers of Rift Valley fever after the 2013-14 outbreak in Senegal using serological data in small ruminants.

Ismaila Seck,Cécile Squarzoni-Diaw,Andrea Apolloni,Baba Sall,Rianatou Bada Alambedji,Assane Gueye Fall,Caroline Coste,Coumba Faye,Modou Moustapha Lo,Mbargou Lo,Renaud Lancelot,Mariane Diop,Catherine Béatrice Cêtre-Sossah,Adji Mareme Gaye,Mamadou Ciss

doi:10.1371/journal.pntd.0010024

Abstract

Rift Valley fever (RVF) is a mosquito-borne disease mostly affecting wild and domestic ruminants. It is widespread in Africa, with spillovers in the Arab Peninsula and the southwestern Indian Ocean. Although RVF has been circulating in West Africa for more than 30 years, its epidemiology is still not clearly understood. In 2013, an RVF outbreak hit Senegal in new areas that weren’t ever affected before. To assess the extent of the spread of RVF virus, a national serological survey was implemented in young small ruminants (6–18 months old), between November 2014 and January 2015 (after the rainy season) in 139 villages. Additionally, the drivers of this spread were identified. For this purpose, we used a beta-binomial () logistic regression model. An Integrated Nested Laplace Approximation (INLA) approach was used to fit the spatial model. Lower cumulative rainfall, and higher accessibility were both associated with a higher RVFV seroprevalence. The spatial patterns of fitted RVFV seroprevalence pointed densely populated areas of western Senegal as being at higher risk of RVFV infection in small ruminants than rural or southeastern areas. Thus, because slaughtering infected animals and processing their fresh meat is an important RVFV transmission route for humans, more human populations might have been exposed to RVFV during the 2013–2014 outbreak than in previous outbreaks in Senegal.

Highlights

Rift Valley fever (RVF) is a zoonosis disease affecting wild and domestic ruminants, caused by an arbovirus that belongs to the genus Phlebovirus in the family Phenuiviridae of the order Bunyavirales [1]
In the model-selection process, we considered the addition of two-way interactions on the basis of their plausibility given our expertise on RVF epidemiology in this region
The seroprevalence was highly heterogeneous in space, with many villages (40.6%), showing a null value mixed together with other villages with a high RVF virus (RVFV) seroprevalence (Fig 1B)

Summary

Introduction

Rift Valley fever (RVF) is a zoonosis disease affecting wild and domestic ruminants, caused by an arbovirus that belongs to the genus Phlebovirus in the family Phenuiviridae of the order Bunyavirales [1]. The RVF virus (RVFV) is transmitted through (i) the bites of competent mosquito vectors, and/or (ii) contact with the body fluids of infected ruminants, the latter being the major route of transmission for human infection [2]. During RVF epidemics, the virus has been detected in many mosquito species belonging to at least 6 genera: Aedes, Anopheles, Culex, Eretmapodites, Coquillettidia, and Mansonia [3]. A few species of the Culex and Aedes genera appear to be the most suitable vectors for RVFV transmission [4]. Wild ruminants can act as a reservoir for the transmission and maintenance of the RVFV

Results

Discussion

Conclusion