First isolation of the Rift Valley fever virus from Culex poicilipes (Diptera: Culicidae) in nature.

Abstract

Abstract. Following the reemergence of Rift Valley fever (RVF) virus in southeastern Mauritania in 1998, an entomological survey was undertaken in the boundary area in Senegal to assess the extent of the virus circulation. During this study, RVF virus (36 strains) was isolated for the first time from Culex poicilipes in nature. The possible role of Cx. poicilipes as an RVF vector is discussed regarding its biology and ecology. Rift Valley fever (RVF) is an African viral zoonosis transmitted by mosquitoes. In September and October 1998, hemorrhagic fever cases were reported in the Ayoun El Atrouss zone, Mauritania (Nabeth P, unpublished data). Rift Valley fever virus was diagnosed using IgM capture, reverse transcriptase-polymerase chain reaction (RT-PCR), and virus isolation at the Pasteur Institute, Dakar, Senegal. Following the confirmation of these RVF cases in Mauritania, entomological survey was carried out in Senegal along the river basin in Thille Boubacar, Kanel, Dembankane, and Diawara ( Figure 1) in order to evaluate the extent of virus circulation. These localities are approximately 400 kilometers from the Mauritanian epidemic/epizootic zone.Mosquitoes were collected using the Centers for Disease Control and Prevention (CDC) light traps with CO 2 set nearby temporary ground pools and CDC light traps without CO 2 set in sheepfolds or cowsheds. They were then sorted and classified into monospecific pools and stored in liquid nitrogen before virological isolation attempts were made. Isolations were performed on Vero and AP 61 (Aedes pseudoscutellaris) cell lines. Rift Valley fever virus identification was made by indirect immunofluorescence, 1 then confirmed by complement fixation and seroneutralization tests.In total, 31,944 mosquitoes belonging to 6 genera and 20 species were captured. Culex poicilipes and Mansonia uniformis were the most common species (Table 1). Thirty-six RVF virus strains were isolated from Cx. poicilipes captured in Diawara, the locality in which the highest density of Cx. poicilipes was obtained (Figure 2). The true infection rate was estimated to be 0.37 Ϯ 0.06% in Diawara.To our knowledge, this is the first isolation of RVF virus from Cx. poicilipes in nature. Among mosquitoes collected, Culex antennatus, Anopheles pharoensis, Mansonia africana and Ma. uniformis were already found naturally infected by the RVF virus. 2 Previously, RVF virus isolations were obtained in Senegal from mosquitoes Aedes dalzieli, Aedes vexans, and Aedes ochraceus. 3 Like most RVF virus vectors, Cx. poicilipes is a temporary-ground-pools mosquito well adapted to the Sahelian area. In Barkedji area where an entomological survey has been conducted since 1990, Cx. poicilipes is the most represented species after Ae. vexans. 3 In this area, a high tropism of Cx. poicilipes was observed for

A Review of Mosquitoes Associated with Rift Valley Fever Virus in Madagascar

“…Dam construction and ecological modification of the environment, including the presence of rice fields, may lead to the outbreaks directly associated with vector abundance. 24,25 Mosquitoes can become infected by feeding on an infected host that exhibits a viremia higher than 10 1.3 plaque-forming unit (pfu)/mL. 26 RVFV can be transmitted to vertebrates and mosquitoes by several mechanisms.…”

“…Nine of them are already reported in the field to be RVFV-positive in Africa and Madagascar. 9,19,25,[38][39][40][41] One Eretmapodites species and two Mansonia species also could be potential vectors in Madagascar.…”

Decision Making Environment on Rift Valley Fever in Ferlo (Senegal)

“…This disease, conveyed by arthropod vectors (Diallo et al 2000), is caused by a virus of the Bunyaviridae family Phlebovirus kind. The RVF can be transmitted by two main modes: the vectorial transmission mode by some blood-sucking insects and the direct transmission mode by personal contact with an infected host (Greboval 2003).…”

Global health

“…Moreover, Glossina spp., better known as tsetse fly, play an important role as vector of the human sleeping sickness. Diallo et al (2000) estimated the infection rate of Culex poicilipes in Mauretania to 0.37 ± 0.06 %. For a complete list of all to date identified as well as potential mosquito vectors please refer to Pfeiffer et al (2005).…”