Spatial multi-criteria evaluation: a promising methodology for identifying areas at risk of Rift Valley fever

14 habits, and the potential but unevaluated impacts of climate change on the distribution, abundance and competence of vectors, the disease now threatens North and East African countries that share borders with infected countries, and European countries where potential vectors are present (Chevalier et al., 2010; Moutailler et al., 2008). Given the lack of knowledge about factors triggering emergence in infected areas, and the unpredictability of outbreaks – with the exception of Kenya, where a link was clearly demonstrated between extreme rainfall events and outbreak occurrence (Linthicum et al., 1999) – there is need to develop pragmatic approaches to provide risk maps in a context where data are scarce and other significant knowledge gaps exist. Spatial multi-criteria evaluation (MCE) and multi-criteria decision analysis (MCDA) are relatively rapid and pragmatic methods for mapping disease risk in the absence of large epidemiological data sets. Geographic Information System (GIS)-based MCE processes transform and combine geographical data and value judgements – derived from expert knowledge and the literature including subjective and qualitative information, and uncertainties can be reduced when control measures such as vaccination, insecticide spraying and stakeholder communication are quickly implemented. The delay between case detection and the implementation of control measures depends on factors that include the efficiency of surveillance networks and the rapid reaction of animal and human health authorities. First recognized in 1931 (Gerdes, 2004), RVF disease is endemic in sub-Saharan Africa, and was thought to be confined to the African continent, including Madagascar, until it spread to the Arabian Peninsula in 2000 (Ahmad, 2000). Recent outbreaks were recorded in the Horn of Africa, first in Kenya (CDC, 2007), Somalia and the United Republic of Tanzania (WHO, 2007) in 2006– 2007; then in the Sudan (Adam, Karsany and Adam, 2010) and Madagascar in 2008 (Andriamandimby et al., 2010). Outbreaks occurred in South Africa in 2008, 2009, 2010 and 2011 (Métras et al., 2013), and in Mauritania in 2010 (El Mamy et al., 2011; OIE, 2009); the last large outbreak occurred in 2012–2013 in Senegal (Sow et al., 2014; Chevalier et al., 2005; ProMED, 2013). As a result of intensification of the international trade in live animals, nomadic Rift Valley fever (RVF), caused by a Phlebovirus (Bunyaviridae), is considered one of the most important viral zoonoses in Africa, affecting both livestock and humans (Pépin et al., 2010). The virus is transmitted: i) between ruminants, by mosquitoes and perhaps by direct contact with viraemic blood, abortion products or other excretions and secretions from viraemic animals (Nicolas et al., 2014); and ii) from ruminants to humans, by direct and mosquitoborne routes (Pépin et al., 2010). The health and economic consequences of RVF outbreaks are severe. In ruminants, RVF infection causes abortion storms in pregnant females and acute deaths in newborn young. Although RVF virus (RVFV) causes an influenza-like syndrome in most human cases, a minority of these cases lead to severe forms of disease such as haemorrhagic fever, encephalitis or hepatitis. As well as its direct effects on animal and human health, RVF has important economic consequences at both the local and national levels. The most direct impacts of RVF on the pastoralist community are the loss of income, and potential food insecurity resulting from this lost income and from ruminant mortality/ morbidity (Peyre et al., 2014). This impact © FA O /S ar ah E lli ot t Spatial multi-criteria evaluation: a promising methodology for identifying areas at risk of Rift Valley fever PERSPECTIVES