Survey and entomological characterization of mosquitoes as potential vectors of arboviruses, in Mozambique

Abstract

Mosquito-borne diseases such as arboviruses represent expanding threats to sub-Saharan Africa, imposing a considerable burden on human and veterinary public health. Mozambique is located in a region suitable for arboviruses outbreaks. Increasingly available evidence suggests that the country is endemic to various debilitating and life-threatening arboviral diseases such as dengue (DEN), Rift Valley fever (RVF), chikungunya (CHIK) and others. Thus, the goal of this thesis is to describe the occurrence and distribution of mosquito arboviruses vectors in Mozambique and detect in them the presence of arbovirus. The thesis includes a total of three (I-III) studies that culminated with four (I-IV) manuscripts. Study I (Papers I and II) aimed at determining the occurrence and distribution of immature mosquitoes with the potential for transmitting arboviruses. Between March and April 2016, a cross-sectional study was conducted in 32 districts to determine the distribution and breeding sites of Ae. aegypti and Ae. albopictus. Aedes aegypti was found in every sampled district, while Ae. albopictus was only found in Moatize district (Tete Province). This study detected the occurrence of Ae. luteocephalus for the first time in the country, in the Lago district (Niassa Province). The highest Container Index (CI) of Ae. aegypti was found in used tires (35.3%), cement tanks (32.3%) and drums (22.1%). These results show that the risk of arboviruses transmission is likely to have been underestimated, highlighting the need to establish a solid national entomological surveillance program for Aedes spp. in Mozambique. Study II (Paper III) was mainly to determine the abundance, composition and main drivers with the influence of the dynamics of mosquitoes associated with the transmission of arboviruses in Mopeia (Zambézia Province) and Goba (Maputo Province) districts. Longitudinal surveys were conducted from 2014 to 2015. Mosquitoes were sampled overnight, once a month, using CDC light traps and Tent/Net traps, both bated with CO2. Sporadic collections were also performed in Maputo and Massingir districts. The mosquito population dynamics between sites and climate factors influencing it were investigated. A total of 33,621 mosquitoes were collected, in districts of Mopeia (86.6%) and Goba (12.2%), where a total of 37 and 31 mosquito species were found, respectively. The remaining 1.2% specimens were collected from complementary surveys carried out in Maputo and Massingir districts. The results indicated high diversity of vector species in Goba and Mopeia sites. There was significant variability of abundance and composition between sites season, and a significant association with rainfall and high average monthly air temperature. These findings underscore the need for further investigation on factors contributing to the establishment and abundance of mosquito vectors and arboviruses transmission in the studied sites. Study III (Paper IV) aimed at describing the presence of arbovirus groups in mosquitoes from Mozambique. Overall mosquito collection processes are described in study II. The viral screening was performed by targeting the detection of Alphaviruses, Flaviviruses, and Bunyavirales. The results revealed genetically distinct insect-specific flaviviruses detected in multiple species of mosquitoes from different genera, three lineages of putative members of the Phenuiviridae family, two of which correspond to the novel viral genetic lineages. Despite that pathogenic arboviruses have not been found in the collected mosquitoes, this work still represents an important contribution to inform the establishment of a vector control program for arbovirus in the country. The evidence presented in this thesis may guide the implementation of an integrated mosquito-borne diseases control program in Mozambique.