Abstract
BackgroundChikungunya virus is an alphavirus, primarily transmitted by Aedes aegypti and Ae. albopictus. In late 2017–2018, an outbreak of chikungunya occurred in Mombasa county, Kenya, and investigations were conducted to establish associated entomological risk factors.MethodsHomes were stratified and water-filled containers inspected for immature Ae. aegypti, and larval indices were calculated. Adult mosquitoes were collected in the same homesteads using BG-Sentinel and CDC light traps and screened for chikungunya virus. Experiments were also conducted to determine the ability of Culex quinquefasciatus to transmit chikungunya virus.ResultsOne hundred thirty-one houses and 1637 containers were inspected; 48 and 128 of them, respectively, were positive for immature Ae. aegypti, with the house index (36.60), container index (7.82) and Breteau index (97.71) recorded. Jerry cans (n = 1232; 72.26%) and clay pots (n = 2; 0.12%) were the most and least inspected containers, respectively, while drums, the second most commonly sampled (n = 249; 15.21%), were highly positive (65.63%) and productive (60%). Tires and jerry cans demonstrated the highest and lowest breeding preference ratios, 11.36 and 0.2, respectively. Over 6900 adult mosquitoes were collected and identified into 15 species comprising Cx. quinquefasciatus (n = 4492; 65.04%), Aedes vittatus (n = 1137; 16.46%) and Ae. aegypti (n = 911; 13.19%) and 2 species groups. Simpson’s dominance and Shannon-Wiener diversity indices of 0.4388 and 1.1942 were recorded, respectively. Chikungunya virus was isolated from pools of Ae. aegypti (1) and Cx. quinquefasciatus (4), two of which were males. Minimum infection rates of 3.0 and 0.8 were observed for female Ae. aegypti and Cx. quinquefasciatus, respectively. Between 25 and 31.3% of exposed mosquitoes became infected with CHIKV 7, 14 and 21 days post-exposure. For the experimentally infected Cx. quinquefasciatus mosquitoes, between 13 and 40% had the virus disseminated, with 100% transmission being observed among those with disseminated infection.ConclusionsThese results demonstrated high risk of chikungunya transmission for residents in the sampled areas of Mombasa. Transmission data confirmed the probable role played by Cx. quinquefasciatus in the outbreak while the role of Ae. vittatus in the transmission of chikungunya virus remains unknown.Graphical
Highlights
Chikungunya virus (CHIKV) is a global re-emerging mosquito-borne alphavirus, which was first detected in 1952 along the Tanzania-Mozambique border [1]
Transmission data confirmed the probable role played by Cx. quinquefasciatus in the outbreak while the role of Ae. vittatus in the transmission of chikungunya virus remains unknown
In the sylvatic transmission cycle, a wider range of species is involved including Ae. aegypti, Ae. africanus, Ae. luteocephalus, Ae. furcifer, Ae. taylori, Ae. dalzieli, Ae. metallicus, Ae. neoafricanus, Ae. centropunctatus, Ae. hirsutus, Anopheles domicola, An. funestus, An. coustani, Mansonia uniformis and Culex poicilipes [6,7,8,9,10,11]. Because of these known traditional vectors involved in the urban transmission cycle of CHIKV, entomological surveillance and outbreak response activities are usually biased toward Ae. aegypti or Ae. albopictus as the main vectors, leading to neglect of other species even where their densities and possible involvement in the transmission of this virus should be explored
Summary
Chikungunya virus (CHIKV) is a global re-emerging mosquito-borne alphavirus, which was first detected in 1952 along the Tanzania-Mozambique border [1]. In the sylvatic transmission cycle, a wider range of species is involved including Ae. aegypti, Ae. africanus, Ae. luteocephalus, Ae. furcifer, Ae. taylori, Ae. dalzieli, Ae. metallicus, Ae. neoafricanus, Ae. centropunctatus, Ae. hirsutus, Anopheles domicola, An. funestus, An. coustani, Mansonia uniformis and Culex poicilipes [6,7,8,9,10,11] Because of these known traditional vectors involved in the urban transmission cycle of CHIKV, entomological surveillance and outbreak response activities are usually biased toward Ae. aegypti or Ae. albopictus as the main vectors, leading to neglect of other species even where their densities and possible involvement in the transmission of this virus should be explored. During chikungunya outbreaks in Reunion and Comoros Islands, CHIKV was isolated from Culex P. quinquefasciatus and a pool of Culex spp. mosquitoes, respectively, this was attributed to possible midgut infection and not investigated further [12, 13] This was probably because species other than Ae. aegypti and Ae. albopictus have rarely been associated with CHIKV transmission. In late 2017–2018, an outbreak of chikungunya occurred in Mombasa county, Kenya, and investigations were conducted to establish associated entomological risk factors
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