Detection, Isolation, and Genetic Characterization of Rift Valley Fever Virus fromAnopheles(Anopheles)coustani,Anopheles(Anopheles)squamosus, andCulex(Culex)antennatusof the Haute Matsiatra Region, Madagascar

Abstract

Following veterinary alerts of Rift Valley fever (RVF) in the districts of Fianarantsoa I and II in November 2008 and in the district of Ambalavao in April 2009, entomological and virological investigations were carried out to identify the mosquito species that could act as RVF virus (RVFV) vectors in the region. A total of 12,785 adult mosquitoes belonging to 5 genera and 21 species were collected. After identification, mosquitoes were pooled by species, sex, and female status (fed or unfed) and then stored at -80°C. Of 319 pools of unfed monospecific female mosquito tested by real-time RT-polymerase chain reaction, RVFV was detected in 1 pool of Anopheles coustani, 5 pools of An. squamosus, and 2 pools of Culex antennatus mosquitoes. The virus was isolated in mosquito cell lines from two of the five Real Time-RT-polymerase chain reaction (real time-RT-PCR) positive pools of An. squamosus mosquitoes. From the eight RVFV strains detected, partial S, M, and L genome segments sequences were obtained. The phylogenetic analysis of these sequences showed that the strains circulating in mosquitoes were genetically close to those that circulated in livestock and humans during RVF outbreaks in 2008 and 2009. This study, therefore, provides strong evidence that An. squamosus, An. coustani, and Cx. antennatus could play a role as vectors of the RVFV during the disease outbreaks in 2008-2009. Bioecological, genetic, and RVF transmission studies on these three mosquito species are needed to address this question and thus improve prevention and control of future RVF outbreaks in Madagascar, where these species are present.

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

“…10,11 Twenty years later, in 2008 and 2009, an RVF outbreak was reported in several regions of the island with virus detection and isolation in mosquitoes, humans, and livestock. 4,9 As supporting evidence, anti-RVFV (immunoglobulin M [IgM] and IgG) antibodies have been detected in livestock and humans during periods between virus outbreaks. 12,13 These results suggest a silent but continuous circulation of the virus in livestock.…”

“…Five Anopheles species are associated or potentially associated with RVF transmission; all are zoophilic or zooanthropophilic taxa, 33 and three species are reported to be infected with RVFV in continental Africa and Madagascar. 9,21 Ten Culex vector species associated with RVF infection are present in Madagascar. Nine of them are already reported in the field to be RVFV-positive in Africa and Madagascar.…”

“…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.…”

“…uniformis. 9,42 Recently considered as an RVFV candidate vector, 15 Cx. antennatus also has a high vector competence.…”

“…7 The role of mosquitoes in RVF transmission on the island was considered to be associated with the first RVFV isolation and the 2008-2009 outbreak. 8,9 Even given the presence of 32 mosquito species in Madagascar that are known or suspected vectors of RVFV, little information is available for these taxa from an entomological perspective. Herein, we focus on the mosquito species present in Madagascar associated with RVFV transmission based on data in the literature.…”