Rift Valley fever virus (family Bunyaviridae, genus Phlebovirus). Isolations from Diptera collected during an inter-epizootic period in Kenya

Abstract

A total of 134 876 Diptera collected in Kenya during a 3-year period were tested in 3383 pools for Rift Valley fever (RVF) virus. Nineteen pools of unengorged mosquitoes were found positive for RVF. All isolations were made from specimens collected at or near the naturally or artificially flooded grassland depressions that serve as the developmental sites for the immature stages of many mosquito species. The isolation of virus from adult male and female A. lineatopennis which had been reared from field-collected larvae and pupae suggests that transovarial transmission of the virus occurs in this species.

Rift Valley fever: a sero-epidemiological survey among pregnant women in Mozambique

“…Residents of areas near water sources where cattle were kept had higher levels of antibody prevalence, although current possession of household domestic animals did not seem to be important. Studies in Kenya suggest that RVFV is maintained in nature through transovarial transmission in floodwater Aedes mosquitoes and that further virus amplification occurs in particularly rainy years when arthropods feed on cattle (Linthicum et al 1985). These findings may explain our results.…”

Prediction of a Rift Valley fever outbreak

“…Dambos are low-lying areas that flood in the wet season and form an essential part of the soil catenas in East and Southern Africa (20). The flooding of dambos induces the hatching of transovarially infected Aedes mcintoshi mosquito eggs that are dormant in the soil, producing infected adult females in 7-10 days that can transmit RVF virus to domestic animals (1,22,25). After a blood meal, the Aedes mosquitoes will lay infected eggs on moist soil at the edge of mosquito habitats, but appear to not be an efficient secondary vector of the virus between infected and noninfected domestic animals and humans (25,26).…”

“…The flooding of dambos induces the hatching of transovarially infected Aedes mcintoshi mosquito eggs that are dormant in the soil, producing infected adult females in 7-10 days that can transmit RVF virus to domestic animals (1,22,25). After a blood meal, the Aedes mosquitoes will lay infected eggs on moist soil at the edge of mosquito habitats, but appear to not be an efficient secondary vector of the virus between infected and noninfected domestic animals and humans (25,26). However, Culex species mosquito vectors subsequently colonize these flooded dambos and, with a delay of several weeks, large populations of these mosquitoes emerge and efficiently transmit the virus from domestic animals, which amplify the virus, to noninfected domestic animals and humans (22,25,26).…”

“…After a blood meal, the Aedes mosquitoes will lay infected eggs on moist soil at the edge of mosquito habitats, but appear to not be an efficient secondary vector of the virus between infected and noninfected domestic animals and humans (25,26). However, Culex species mosquito vectors subsequently colonize these flooded dambos and, with a delay of several weeks, large populations of these mosquitoes emerge and efficiently transmit the virus from domestic animals, which amplify the virus, to noninfected domestic animals and humans (22,25,26). By using information gained from previous RVF outbreaks (2, 12, 25, Fig.…”

Patterns of Rift Valley fever activity in Zambia

“…There is evidence to suggest that Aedes mcintoshi can transmit RVF transovarially and is responsible for initiating epizootics of RVF, which then recruit other vector species for its propagation [4,5]. The flooded dambos are also favoured breeding sites for a variety of mosquito species, which are capable of transmitting RVF [4,6,7].…”