A survey of mosquito-borne and insect-specific viruses in hospitals and livestock markets in western Kenya

Abstract

Aedes aegypti and Culex pipiens complex mosquitoes are prolific vectors of arboviruses that are a global threat to human and animal health. Increased globalization and ease of travel have facilitated the worldwide dissemination of these mosquitoes and the viruses they transmit. To assess disease risk, we determined the frequency of arboviruses in western Kenyan counties bordering an area of high arboviral activity. In addition to pathogenic viruses, insect-specific flaviviruses (ISFs), some of which are thought to impair the transmission of specific pathogenic arboviruses, were also evaluated. We trapped mosquitoes in the short and long rainy seasons in 2018 and 2019 at livestock markets and hospitals. Mosquitoes were screened for dengue, chikungunya and other human pathogenic arboviruses, ISFs, and their blood-meal sources as determined by high-resolution melting analysis of (RT-)PCR products. Of 6,848 mosquitoes collected, 89% were trapped during the long rainy season, with A. aegypti (59%) and Cx. pipiens sensu lato (40%) being the most abundant. Most blood-fed mosquitoes were Cx. pipiens s.l. with blood-meals from humans, chicken, and sparrow (Passer sp.). We did not detect dengue or chikungunya viruses. However, one Culex poicilipes female was positive for Sindbis virus, 30 pools of Ae. aegypti had cell fusing agent virus (CFAV; infection rate (IR) = 1.27%, 95% CI = 0.87%-1.78%); 11 pools of Ae. aegypti had Aedes flavivirus (AeFV; IR = 0.43%, 95% CI = 0.23%-0.74%); and seven pools of Cx. pipiens s.l. (IR = 0.23%, 95% CI = 0.1%-0.45%) and one pool of Culex annulioris had Culex flavivirus. Sindbis virus, which causes febrile illness in humans, can complicate the diagnosis and prognosis of patients with fever. The presence of Sindbis virus in a single mosquito from a population of mosquitoes with ISFs calls for further investigation into the role ISFs may play in blocking transmission of other arboviruses in this region.

Molecular prevalence and risk factors associated with tick-borne pathogens in cattle in western Kenya

“…Outside outbreak phases, the viraemia caused by CCHF and Rift Valley fever in reservoir hosts such as cattle may be lower than the PCR detectable limits [ 76 ]; hence the combined use of PCR and serology may give a clearer picture of their occurrence. This challenge is also reflected in the low infection rates of these arboviruses in their major vectors, such as ticks and mosquitoes collected from the same sampling sites [ 26 , 77 ]. Moreover, arboviruses, such as dengue and chikungunya, have limited enzootic cycles and cattle do not seem to be play a key role in their maintenance [ 78 , 79 ].…”

Culex tarsalis is a competent host of the insect-specific alphavirus Eilat virus (EILV)

“…Although insect-specific viruses are thought to be adapted to a single host 11,12,[21][22][23][24][25] , it remains possible that EILV does not match this framework, instead infecting multiple mosquito taxa. While most ISVs are flaviviruses 26 , only a few insect-specific alphaviruses have ever been described [4][5][6] , and they may not conform to the patterns described in other ISVs. Mosquito species reported to have host competence for EILV now include An.…”

Molecular screening reveals non-uniform malaria transmission in western Kenya and absence of Rickettsia africae and selected arboviruses in hospital patients

“…However, outside outbreak phases, circulation of arboviruses is very low and it is therefore challenging to detect clinical/acute cases [ 22 , 67 ]. This is also reflected in the low infection rates of the vector mosquito species from the same region, where only one pool of Culex mosquitoes was positive for Sindbis virus, in combination with a comparatively high infection rate with insect-specific flaviviruses [ 35 ]; the latter are thought to block superinfection of vectors with pathogenic viruses [ 68 ]. On the other hand, Plasmodium spp.-chikungunya dual infection has been shown to cause interferon gamma induced suppression of viraemia and joint pathology caused by arthralgic alphaviruses [ 69 ].…”

“…For the purpose of this study, 336 of 865 blood samples collected throughout the study, and associated demographic data were selected, based on the following criteria: (i) blood samples collected from patients with fever and other clinical features associated with febrile illness (Fig. 2 ) between January 2018 and February 2019, corresponding to the period ticks and mosquitoes positive for CCHF and Sindbis viruses, respectively, were collected from the same study site [ 10 , 35 ], (ii) availability of complete meta-data, and (iii) adequate blood volume to conduct all analyses. Selected samples were thawed, aliquoted and transported on ice (0–5 °C) to the Martin Lüscher Emerging Infectious Disease (ML-EID) laboratory at the International Centre of Insect Physiology and Ecology ( icipe ) where nucleic acid extraction was performed on arrival and then stored at −80 °C for subsequent molecular analyses.…”