Evidence of Rift Valley fever seroprevalence in the Sahrawi semi-nomadic pastoralist system, Western Sahara.

Antonello Di Nardo,Annapia Di Gennaro,Sidumu J Hamdi,Davide Rossi,Saleh M Lejlifa,Saleh M Saleh,Michael V Thrusfield,Giovanni Savini

doi:10.1186/1746-6148-10-92

Abstract

BackgroundThe increasing global importance of Rift Valley fever (RVF) is clearly demonstrated by its geographical expansion. The presence of a wide range of host and vector species, and the epidemiological characteristics of RVF, have led to concerns that epidemics will continue to occur in previously unaffected regions of Africa. The proximity of the Sahrawi territories of Western Sahara to endemic countries, such as Mauritania, Senegal, and Mali with periodic isolation of virus and serological evidence of RVF, and the intensive livestock trade in the region results in a serious risk of RVF spread in the Sahrawi territories, and potentially from there to the Maghreb and beyond. A sero-epidemiological survey was conducted in the Saharawi territories between March and April 2008 to investigate the possible presence of the RVF virus (RVFV) and associated risk factors. A two-stage cluster sampling design was used, incorporating 23 sampling sites.ResultsA total of 982 serum samples was collected from 461 sheep, 463 goats and 58 camels. Eleven samples (0.97%) tested positive for IgG against the RVFV. There were clusters of high seroprevalence located mostly in the Tifariti (7.69%) and Mehaires (7.14%) regions, with the Tifariti event having been found in one single flock (4/26 positive animals). Goats and older animals were at a significantly increased risk being seropositive (p = 0.007 and p = 0.007, respectively).ConclusionThe results suggest potential RVF activity in the study area, where intense livestock movement and trade with neighbouring countries might be considered as a primary determinant in the spread of the disease. The importance of a continuous field investigation is reinforced, in light of the risk of RVF expansion to historically unaffected regions of Africa.

Highlights

The increasing global importance of Rift Valley fever (RVF) is clearly demonstrated by its geographical expansion
In 1975, as a consequence of the military occupation of Western Sahara by Mauritanian and Moroccan military forces, about 70,000 Sahrawi fled into Algeria [12,13] where they gathered in refugee camps in the Tindouf province
Rift valley fever seroprevalence Field constraints limited the scope of the survey and only a total of nine hundred and eighty two animals were sampled in 23 sites

Summary

Introduction

The increasing global importance of Rift Valley fever (RVF) is clearly demonstrated by its geographical expansion. The presence of a wide range of host and vector species, and the epidemiological characteristics of RVF, have led to concerns that epidemics will continue to occur in previously unaffected regions of Africa. Rift Valley fever can induce substantial economic losses through high abortion rates and death of neonates and young animals during epidemics. It incurs heavy control costs, including those of culling and compensation, vaccination and vector control [4]. The ability of RVF to move outside traditionally endemic countries, even out of the African continent, lies in the fact that a large range of arthropod vectors is capable of transmitting the virus; the level of viraemia in ruminants is sufficiently high to infect mosquitoes [9]. This transboundary animal disease has the potential to spread over large distances, deserving further consideration in a world where globalisation of trade and short transportation times are common

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