Simultaneous circulation of two West Nile virus lineage 2 clades and Bagaza virus in the Zambezi region, Namibia

Abstract

Flaviviruses include a great diversity of mosquito-borne arboviruses with epidemic potential and high global disease burden. Several flaviviruses are circulating in southern Africa affecting humans and livestock, among them West Nile virus (WNV) and Wesselsbron virus. Despite their high relevance, no arbovirus surveillance study has been conducted for more than 35 years in Namibia. In this study we assessed the diversity of flaviviruses circulating in mosquitoes in the densely populated, semi-tropical Zambezi region of north-eastern Namibia. In total, 10,206 mosquitoes were sampled in Bwabwata and Mudumu national parks and Mashi and Wuparo conservancies and screened for flavivirus infections. A high infection rate with insect-specific flaviviruses was found with 241 strains of two previously known and seven putative novel insect-specific flaviviruses. In addition, we identified ten strains of WNV in the main vector Cx. univittatus sampled in the Mashi conservancy. Surprisingly, the strains fell into two different clades of lineage 2, 2b and 2d. Further, three strains of Bagaza Virus (BAGV) were found in Cx. univittatus mosquitoes originating from Mudumu national park. Assessment of BAGV growth in different cell lines showed high replication rates in mosquito and duck cells and about 100,000fold lower replication in human, primate and rodent cells. We demonstrate a wide genetic diversity of flaviviruses is circulating in mosquitoes in the Zambezi region. Importantly, WNV and BAGV can cause outbreaks including severe disease and mortality in humans and birds, respectively. Future studies should focus on WNV and BAGV geographic distribution, as well as on their potential health impacts in and the associated social and economic implications for southern Africa.

Dynamic Surveillance of Mosquitoes and Their Viromes in Wuhan During 2020

“…Many Culex flavivirus strains have been reported in Culex from different parts of the world. Interestingly, Culex flavivirus and West Nile virus co-infection in mosquitoes are positively correlated [38,39]. CtFLV has recently been identified from the local Culex in Japan and is closely associated with Shayang fly virus 4, which was previously identified in Hubei Province.…”

Bagaza virus in wild birds, Portugal, 2021

“…In addition, efforts are needed to identify the vectors for BAGV in Portugal and their role on the epidemiology of disease. Culex univittatus is one of the putative competent vectors (10) detected by the nationwide surveillance of haematophagous arthropods in Portugal (REVIVE). Despite the high similarity between the strains from the 2021 outbreak in Portugal and those from Cádiz 2010 (Southern Spain), given the small size of the sequences produced, further genomic analysis is needed to elucidate the phylogenetic relationships with previously known BAGV strains.…”

“…perexiguus in United Arab Emirates (9) and Cx. univittatus in Namibia (10). In vertebrates, BAGV associated-deaths were first detected in red-legged partridges ( Alectoris rufa ) and ring-necked pheasants ( Phasianus colchicu ) in Spain in 2010 (2), and a few years later, in 2016, in Himalayan monal ( Lophophorus impejanus ) in South Africa (6).…”

Flavivirus Persistence in Wildlife Populations

“…USUV has also been shown to transmit between mosquitoes and canines, deer, and boars, as well as bats and rodents [ 37 ]. Moreover, for mosquito arboviruses, incredibly little is known about the nature of the vertebrate host [ 38 ]. Therefore, more work into the elucidation of host-species interactions is essential for the determination of flavivirus persistence in wildlife.…”