empres watch VOL 34 - December 2015
Contributors: Claudia Pittiglioa , Julio Pintoa , Susanne Münstermann b, Pierre Formentyc , Juan Lubrotha , Stephane de la Rocquec , Eran Raizmana , Daniel Beltran-Alcrudoa a Food and Agriculture Organization of the United Nations (FAO); b World Organisation for Animal Health (OIE); c World Health Organization (WHO)
Introduction
Rift Valley fever (RVF) is a zoonotic, viral, vector-borne disease representing a threat to human health, animal health and livestock production in Africa, the Near East and potentially, Europe and the rest of the world.
Rift Valley fever primarily affects sheep, goats, cattle, camels, buffaloes, and antelopes. The majority of human infections result from contact with the blood or organs of infected animals (Figure 1). The socioeconomic impact of the disease on people’s livelihoods and on trade can be high due to significant losses in livestock production (meat and milk), closure of livestock markets and bans on livestock movement and slaughtering. In Kenya, the RVF epidemic that occurred in 2006–2007 induced estimated losses to the economy of more than 2.1 billion Kenyan Shillings (USD32 million) and extended to various stakeholders in the marketing chain (Rich and Wanyioke, 2010).
Other negative impacts included losses in production, increases in unemployment, and a reduction in operating capital among slaughterhouses and butchers.
Outbreaks of RVF are closely associated with periods of heavy rains and prolonged flooding, which increase habitat suitability for vector populations. These factors can drive vector abundance and population dynamics, thus influencing the risk of disease emergence, transmission and spread (Anyamba et al., 2012). In East Africa, RVF epidemics take place periodically every 10 years and are associated with periods of heavy rainfall that occur during the warm phase of the El Niño/ Southern Oscillation (ENSO) phenomenon (Anyamba et al., 2012). These findings have enabled the successful development of forecasting models and early warning systems for RVF based on satellite images and weather/climate forecasting data that allow authorities to predict RVF outbreaks, identify potential RVF risk areas and thereby to implement measures to prevent their emergence and mitigate their consequences (Anyamba et al., 2010). In 2006–2007, a climate-based model developed by the Goddard Space Flight Center (GSFC) of the National Aeronautics and Space Administration (NASA), predicted the risk of RVF occurrence in the Horn of Africa several weeks before the first signs of the disease were recorded in livestock and humans. This facilitated strategic preparedness and significantly enhanced field response (FAO, 2006; WHO, 2006; Anyamba et al., 2010). In contrast, accurate, climatebased early warning systems have not yet been fully elucidated for West Africa because drivers of RVF emergence and spread are not as well known for that region. Outbreaks of RVF in Senegal and Mauritania are associated with different patterns of precipitation anomalies and the effect of El Niño or other climate-affecting phenomena are still poorly understood.
The Goddard Space Flight Center, FAO, WHO, OIE and other partners have been monitoring climatic conditions to forecast the risk of RVF vector amplification in East Africa for the past few years, and have provided recommendations and early warning messages for countries at risk of RVF outbreaks on several occasions. During the past twelve months there has been an increasing concern about the predicted El Niño event and its impact on public and animal health, particularly in Africa. In December 2014, FAO, OIE and WHO issued an awareness communication based on the information provided by the GSFC and climate models on El Niño.
The purpose of this communication is to warn countries in East Africa about the increased risk of occurrence of RVF outbreaks associated with the El Niño event forecasted in late 2015 and 2016.