Human biting activity, resting behavior and yellow fever virus transmission potential of Aedes mosquitoes in southwest Ethiopia

BackgroundYellow fever is an emerging and re-emerging viral disease transmitted through the bites of infective Aedes mosquitoes. Several outbreaks of yellow fever have been documented in southern Ethiopia.Understanding the transmission cycle is pivotal to manage arboviral disease outbreaks. Therefore, the present study aimed to evaluate which species of Aedes mosquitoes contribute to the YF virus transmission and the outbreaks that have occurred, and their behaviors (biting and resting) in the region. MethodsTwo districts were selected based on previous Yellow Fever (YF) outbreak history. A longitudinal entomological sampling was carried out to collect adult Aedes mosquitoes using human landing catches, mechanical mouth aspirators and pyrethrum spreadsheet collection. Adult mosquito collections were conducted twice a month for six months from February 2019 to July 2020. Identification of mosquito species at the genus level was done using morphological keys and speciation using molecular techniques. Aedes mosquitoes were pooled and tested for YFV, dengue virus (DENV, serotype 1-4) and chikungunya virus (CHKV) by qPCR. Principal findingsA total of 1582 Aedes mosquitoes were collected; 669 (42.3%) from Boko Dawula and 913 (57.7%) from Ofa district. Of the 406 Aedes mosquitoes molecularly characterized to the species level, the Aedes simpsoni complex accounted for 99.5% (404/406), while Aedes aegypti found in the Ofa district accounted for only 0.5% (2/ 406). From the 934 Aedes simpsoni tested for viruses and none were positive. The human biting activities of Aedes (Ae.) simpsoni peaked at 8:00 - 9:00 hour and 16:00 - 17:00 hour, mostly outdoors, both within the villages and forests. The leaves of Ensete (E.) ventricosum appear to be ideal resting places for Aedes (Ae.) simpsoni complex. ConclusionAlthough the tested Ae. simpsoni complex was negative for arboviruses; morning and afternoon activities of the species coincide with human outdoor activities and may therefore pose the risk of viral infection. The lower dominance of Aedes aegypti indicated that the major responsible vector for the occurrences of previous and current arboviral diseases was due to other mentioned Aedes species. It is of great importance to improve surveillance activities of arboviruses in reservoir hosts and vectors to establish control measures. Furthermore, the origin of bloodmeal and the mosquitos role in the transmission of arboviral diseases need further study to improve the understanding of this species. Author SummaryAedes mosquitoes are the vector of most arboviruses infecting humans and animals. In Ethiopia, yellow fever (YF) outbreak is frequently occurring and claiming the lives of several people. Therefore, understanding the cycle of transmission is crucial in designing the prevention and control strategies for YF outbreaks. We conducted an entomological sampling in two districts with recent YF outbreaks in southwestern Ethiopia to identify and characterize the behavior and ecology of the Aedes mosquito species playing role in transmission. The Ae. simpsoni complex was the predominant species identified in both study areas and tends to bite humans in the morning and afternoon when most people are active outdoors within the villages and forests. Although none of the tested Ae. simpsoni complex mosquitoes were positive for arboviruses, improving surveillance activities in reservoir hosts, including primates and vectors, could be a key to establishing prevention and control strategies.