Re-Introduction of West Nile Virus Lineage 1 in Senegal from Europe and Subsequent Circulation in Human and Mosquito Populations between 2012 and 2021

Abstract

West Nile virus (WNV) is a virus of the Japanese encephalitis antigenic complex and belongs to the family Flaviviridae of the genus flavivirus. The virus can cause infection in humans which in most cases is asymptomatic, however symptomatic cases exist and the disease can be severe causing encephalitis and meningoencephalitis. The virus is maintained in an enzootic cycle involving mosquitoes and birds, humans and other mammals such as horses can be accidental hosts. A mosquito-based arbovirus surveillance system and the sentinel syndromic surveillance network (4S) have been in place since 1988 and 2015 respectively, to better understand the transmission dynamics of arboviruses including WNV in Senegal. Arthropod and human samples have been collected from the field and analysed at Institut Pasteur de Dakar using different methods including RT-PCR, ELISA, plaque reduction neutralization test and viral isolation. RT-PCR positive samples have been analysed by Next Generation Sequencing. From 2012 to 2021, 7912 samples have been analysed and WNV positive cases have been detected, 20 human cases (19 IgM and 1 RT-PCR positive cases) and 41 mosquito pools. Phylogenetic analyzes of the sequences of complete genomes obtained showed the circulation of lineage 1a, with all these recent strains from Senegal identical to each other and very close to strains isolated from horse in France in 2015, Italy and Spain. Our data showed lineage 1a endemicity in Senegal as previously described, with circulation of WNV in humans and mosquitoes. Phylogenetic analyzes carried out with the genome sequences obtained also revealed exchanges of WNV strains between Europe and Senegal which could be possible via migratory birds. The surveillance systems that have enabled the detection of WNV in humans and arthropods should be extended to animals in a one-health approach to better prepare for global health threats.

Spatial and temporal dynamics of West Nile virus between Africa and Europe

“…1 ). This means that the first European introduction probably originated in Senegal around the 1990s, as previously reported by Ndione et al 15 . This hypothesis is further supported by our phylogeographic inference which not only confirms the middle of North and West Africa as the location of the common ancestor of all WNV L1 Clade 1A strains but also traces its origin back to the 19th/20th century.…”

“…This is the first time that such an evolutionary relationship has been disclosed. The genetic similarities observed between i) the 2012-2018 Senegalese and 2015 French strains 15 , all of which are closely related to the group of 2021-22 Italian sequences, and ii) the 2020-2022 Italian and 2012 Senegalese strains and those from Italy (2008 and 2011) and Spain (2020) (Fig. 1 ), further support this new reconstructive theory.…”

“…It appears that some European epidemics were the result of the introduction of WNV African strains. With regard to WNV L1, the first introduction probably occurred more than 25 years ago from Northern-Western African countries to Italy or France, where the strain was first detected in 1998 and 2000, respectively 10 , 15 . WNV L2, on the other hand, was first introduced into Hungary in 2004 14 , but its origin is still uncertain 10 , 16 .…”

Detection of Chikungunya virus in The Gambia through a newly implemented sentinel surveillance program

“…The dual challenge of climate change and pandemics necessitates a comprehensive surveillance approach for (re-)emerging infectious diseases. The syndromic sentinel surveillance system showed its efficiency as a early warning system and outbreak response in Senegal (12,13).…”

Genomic epidemiology of West Nile virus in Europe

“…4 , introduction 3) [ 70 ]. Most outbreaks within this clade have since occurred in Italy where viruses continued to persist through at least to 2022, but this clade has also spread to neighboring Spain and as far as Senegal [ [71] , [72] , [73] ].…”