Assessing Anopheles Vector Species Diversity and Transmission of Malaria in Cross-Border Areas of Côte d'Ivoire
Authors: Yokoly Firmain N. , Zahouli Julien B. Z. , Small Graham , Ouattara Allassane F. , Opoku Millicent , Souza Dziedzom K. de , Koudou Benjamin G. 
Published: September 2020

Abstract
Background Although malaria and Anopheles mosquito vectors are highly prevalent in Côte d'Ivoire, data are still lacking on disease transmission dynamics in cross-border areas. To address this lack of information, we assessed the Anopheles mosquito vector species diversity, the An. gambiae complex members and the transmission of malaria in four cross-border areas of Côte d'Ivoire.Method From July 2016 to December 2017, we collected adult Anopheles mosquitoes in four cross-border health districts of Côte d’Ivoire (Aboisso, Bloléquin, Odienné and Ouangolodougou) using standardized window exit trap (WET) and pyrethrum knockdown spray collection (PSC) methods. We identified collected mosquitoes morphologically at species level and An. gambiae complex members using short interspersed nuclear element-based polymerase chain reaction (SINE-PCR). We analyzed An. gambiae, An. funestus and An. nili specimens for malaria Plasmodium parasite infection using the cytochrome oxidase I gene (COX-I), and malaria prevalence among human population through local Ministry of Health (MoH) statistical yearbooks.Results In total, 281, 754, 1,319 and 2,443 specimens of Anopheles adult females were collected in Aboisso, Bloléquin, Odienné and Ouangolodougou, respectively. We found seven Anopheles species dominated by An. gambiae s.l. (94.8%-99.1%), followed by An. funestus (0.4%-4.3%) and An. nili (0%-0.7%). Among An. gambiae s.l., An. coluzzii predominated in Aboisso (89.2%) and Bloléquin (92.2%), while An. gambiae s.s. was present at the highest frequency in Odienné (96.0%) and Ouangolodougou (94.2%). The Plasmodium sporozoite infection rate in An. gambiae s.l. was highest in Odienné (11.0 %; n = 100) followed by Bloléquin (7.8%, n = 115), Aboisso (3.1%; n = 65) and Ouangologoudou (2.5%; n = 120). In An. funestus, P. falciparum sporozoite infection rate was estimated at 6.2% (n = 32) in Bloléquin, 8.7% (n = 23) in Odienné. No An. funestus specimens were found infected with P. falciparum sporozoite infection in Ouangolodougou and Aboisso. No P. falciparum sporozoite was detected in An. nili specimens in the four health districts. Among the local human populations, malaria prevalence rate was higher in Odienné (39.7%; n = 45,376) and Bloléquin (37.6%; n = 150,205) compared with that in Ouangolodougou (18.3%; n = 131,629) and Aboisso (19.7%; n = 364,585).Conclusion In cross-border health districts of Côte d’Ivoire, Anopheles vector species diversity and abundance and Plasmodium sporozoite infection were high, thus resulting in high transmission of malaria to local populations. An. gambiae and An. funestus were found to be highly Plasmodium-infected in the health districts of Bloléquin and Odienné where malaria prevalence among humans was particularly high. This study provides important information that can be used to guide national malaria control programme strategies in Côte d’Ivoire, mainly in cross-border settings.