The 2000 epidemic of Rift Valley fever in Saudi Arabia: mosquito vector studies

Abstract

Abstract. In mid-September 2000, Rift Valley fever (RVF) virus was diagnosed as the cause of infection in humans and livestock in Jizan Region, Saudi Arabia. This is the first time that this arbovirus has been found outside Africa and Madagascar. Collections of mosquitoes (Diptera: Culicidae) were therefore undertaken (from 25 September to 10 October) at eight sites during the epidemic to obtain mosquitoes for attempted RVF virus isolation. Among 23 699 mosquito females tested, isolations of RVF virus were made from six of 15 428 Culex (Culex) tritaeniorhynchus Giles and from seven of 8091 Aedes vexans arabiensis Patton. Minimum mosquito infection rates per 1000 at sites with infected mosquitoes were 0.3±13.8 Cx. tritaeniorhynchus and 1.94±9.03 Ae. v. arabiensis. Viral activity moved northwards as collecting was in progress and collectors`caught up' with the virus at the two most northerly sites on the last two trapping evenings. Other species occurred in small numbers and were identified but not tested. Both Cx. tritaeniorhynchus and Ae. v. arabiensis were susceptible to RVF virus and transmitted between hamsters, and an additional quantitative test with Cx. tritaeniorhynchus showed that 71±73% of mosquitoes became infected after ingesting 6.9±7.9 log 10 FFU/mL of virus; transmission rates were 10% (post-infection day 14) and 26% (postinfection day 20). It was concluded that both species were vectors on grounds of abundance, distribution, preference for humans and sheep, the virus isolations and vector competence tests.

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

“…16,17 For example, in an arid area, such as the Arabian Peninsula, RVFV transmission by mosquitoes is related to rainfall and water runoff management, with temporary rain pools and floodplains representing favorable vector breeding sites. [18][19][20] In subhumid areas in east Africa, RVF emergence is partly caused by the vertical transmission of the virus in eggs of Aedes spp., especially those belonging to the Neomelaniconion subgenus, 21 that are laid in wetland habitats. In the context of El Niñ oSouthern Oscillation (ENSO) events, wetlands become flooded after abnormally high rainfall, which in turn, favors the hatching of infected Aedes eggs and the development of the immature stages.…”

An Investigation of a Major Outbreak of Rift Valley Fever in Kenya: 2006–2007

“…1 Humans acquire RVF through exposure to the blood, body fluids, or tissues of infected animals, or through bites from infected mosquitoes or, potentially, other biting insects. 2,3 Direct exposure to infected animals can occur during handling and slaughter or through veterinary and obstetric procedures. [4][5][6] The RVF virus was first described in Kenya in 1931.…”

High seroprevalence of Rift Valley fever phlebovirus in domestic ruminants and African Buffaloes in Mozambique shows need for intensified surveillance

“…Silent circulation, due to subclinical infections with RVFPV, was reported in goats and sheep in the Province of Zambezia [34], cattle and African buffaloes in other regions of sub-Saharan Africa [38]. As a result of RVFPV circulation pattern in Mozambique, small outbreaks and sporadic cases of clinical and or economic importance may be overlooked.…”

“…These temperatures, coinciding with the hot rainy season (October to March), favor high rainfall (between 800–1000 mm in the south, and even higher in the central and northern regions) [37], and thus breeding of RVFPV mosquito vectors [38]. …”

“…During the rainy season these rivers overflow, flooding the plains [37], favoring the breeding of RVFPV mosquito vectors [38–40]. …”