Human Biting Activity, Resting Behavior and Yellow Virus Transmission Potential of Aedes Mosquitoes in Southwest Ethi-Opia

Yellow 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. Two 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 on 406 Aedes due to limited laboratory resources (primers and probe, reagents shortage) and budget limits. Aedes mosquitoes were pooled and tested for YFV, dengue virus (DENV, serotype 1-4) and chikungunya virus (CHKV) by qPCR. A total of 1689 mosquitoes 93.7% (1582/1689) of Aedes and 6.3% (107/1689) of Culex were collected. Of the total collected mosquitoes, 58.7% (991/1689) were from Ofa study sites whereas the left 41.3% (698/1689) were from Boko Dawula. 93.5% (1579/1689) of Aedes complex were collected during wet season. Most of the mosquitoes were collected during the wet season 97.9% (1653/1689). Of the 1582 Aedes simpsoni complex, 57.7% (913/1582) were from Ofa district and the remaining 42.3% (669/1582) were from Boko Dawula 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. Although 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 mosquito’s role in the transmission of arboviral diseases need further study to improve the understanding of this species.