RE-EMERGENCE OF RIFT VALLEY FEVER VIRUS IN BARKEDJI (SENEGAL, WEST AFRICA) IN 2002–2003: IDENTIFICATION OF NEW VECTORS AND EPIDEMIOLOGICAL IMPLICATIONS Y. BA, A. A. SALL, D. DIALLO, M. MONDO, L. GIRAULT, I. DIA AND M. DIALLO Institut Pasteur de Dakar, BP 220, Dakar, Senegal ABSTRACT. The Rift Valley fever virus (RVFV) is a threat that must not be neglected, as the consequences of RVFV are dramatic, both for human and animal health. This virus is a zoonotic virus that already has demonstrated a real capacity for re-emerging after long periods of silence, as observed in Barkedji (Senegal, West Africa) in 2002. In this article we present the 2nd emergence in Barkedji after the 1st manifestation in 1993, and for the 1st time the circulation of RVFV during 2 consecutive years among mosquito populations in Senegal. As part of the entomological surveillance program undertaken since 1990 to detect circulation of the RVFV in Barkedji, 108,336 mosquitoes belonging to 34 species and 5 genera were collected in 2002–2003. Aedes vexans and Culex poicilipes, previously known to be vectors of RVFV in Senegal, comprised 88.7% of the total collection. In 2002, Ae. vexans was the most abundant mosquito, followed by Cx. poicilipes; the opposite situation was observed in 2003. In 2002, 29 and 10 RVFV isolates were obtained from Cx. poicilipes (minimum infection rate [MIR] 5 0.13%) and Ae. vexans (MIR 5 0.02%) pools, respectively and the MIR for the 2 species were significantly different (x 2 5 34.65; df 5 1, P , 0.001). In 2003, 7 RVFV strains were isolated from Cx. poicilipes (3, MIR 5 0.03), Mansonia africana (2, MIR 5 0.08), Ae. fowleri (1), and Ma. uniformis (1, MIR 5 0.05). The 3 latter species were found to be associated with RVFV for the 1st time in Senegal. A significant decrease in MIR was observed from 2002 to 2003 (x 2 5 6.28; df 5 1, P 5 0.01) for Cx. poicilipes, the only species involved in the transmission during the 2 sampling years. KEY WORDS Rift Valley fever virus, Barkedji, Senegal, re-emergence, mosquito vectors INTRODUCTION Rift Valley fever is a viral disease that affects livestock and humans in sub-Saharan Africa, Egypt, Madagascar, and the Middle East (Mee- gan and Bailey 1988, Shoemaker et al. 2002). The Rift Valley Fever virus (RVFV) is transmitted to vertebrate hosts through the bites of infected mosquitoes and by aerosol produced by blood or other body fluids of infected animals. Human infections typically start as flu-like illness with fever, weakness, back pain, dizziness, and weight loss, and can evolve to more severe and fatal syndromes including hemorrhage, hepatitis, en- cephalitis, and vision impairment (Laughlin et al. 1979). Animal infection generally leads to high mortality among young animals and abortions among pregnant females (Easterday et al. 1962, Coetzer 1977). The RVFV was 1st isolated in Kenya in 1930 (Daubney et al. 1931). Many epidemic/epizootic outbreaks have been reported—in Madagascar in 1990–1991 (Morvan et al. 1991, 1992a, 1992b), in Egypt in 1977–1978 (Hoogstraal et al. 1979), and in several sub-Saharan countries like Kenya in 1950–1951 and 1997 (Davies et al. 1985, Woods et al. 2002), Mauritania in 1987 and 1998 (Jouan et al. 1988, Nabeth et al. 1999). Several of these emergences have been associated with climate variability possibly associated with wider-scale climate change and ecological perturbations (e.g., excessive rainfall and flooding, irrigation and dam construction) and raise serious concerns about the potential impact of modern agricultural development on recrudescence of epidemics in Africa. The 1st entomological data on RVFV vectors in West Africa came from studies on other arbovi- ruses, for example, yellow fever and dengue. These studies have obtained the virus from Culex antennatus (Becker) in Nigeria in 1967 and 1970, Aedes dalzieli (Theobald) in Senegal in 1974 and 1983, and Ae. furcifer (Edwards) and Ae. cum- minsii (Theobald) in Burkina Faso in 1983. Following the RVFV outbreak in Mauritania in 1987, an entomological and sentinel domestic animal program was been set up to monitor RVFV circulation in Barkedji, an area very active in livestock breeding in the central part of Senegal. The program led to the isolation of the virus (Fontenille et al. 1995) from Ae. vexans (Meigen) and Ae. ochraceus (Theobald) in 1993 in Senegal. Following the second RVFV outbreak in southeastern Mauritania in 1998, entomological investigations were conducted for 2 years in the affected areas and in neighboring areas of Senegal. Overall, 63 RVFV strains were isolated from Cx. poicilipes (Theobald)—36 from Senegal in 1998 and 27 from Mauritania in 1999. These results were the 1st field evidence of natural RVFV infection of Cx. poicilipes, and the 1st isolation of the virus from mosquitoes in Maur- itania, the main West African epidemic and epizootic area. Journal of the American Mosquito Control Association, 28(3):170–178, 2012 Copyright E 2012 by The American Mosquito Control Association, Inc. 170