Contrasted Epidemiological Patterns of West Nile Virus Lineages 1 and 2 Infections in France from 2015 to 2019

Since 2015, annual West Nile virus (WNV) outbreaks of varying intensities have been reported in France. Recent intensification of enzootic WNV circulation was observed in the South of France with most horse cases detected in 2015 (n = 49), 2018 (n = 13), and 2019 (n = 13). A WNV lineage 1 strain was isolated from a horse suffering from West Nile neuro-invasive disease (WNND) during the 2015 episode in the Camargue area. A breaking point in WNV epidemiology was achieved in 2018, when WNV lineage 2 emerged in Southeastern areas. This virus most probably originated from WNV spread from Northern Italy and caused WNND in humans and the death of diurnal raptors. WNV lineage 2 emergence was associated with the most important human WNV epidemics identified so far in France (n = 26, including seven WNND cases and two infections in blood and organ donors). Two other major findings were the detection of WNV in areas with no or limited history of WNV circulation (Alpes-Maritimes in 2018, Corsica in 2018–2019, and Var in 2019) and distinct spatial distribution of human and horse WNV cases. These new data reinforce the necessity to enhance French WNV surveillance to better anticipate future WNV epidemics and epizootics and to improve the safety of blood and organ donations.

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Evidence of West Nile virus lineage 2 circulation in Northern Italy

Veterinary Microbiology ◽

10.1016/j.vetmic.2012.02.018 ◽

2012 ◽

Vol 158 (3-4) ◽

pp. 267-273 ◽

Cited By ~ 68

Author(s):

G. Savini ◽

G. Capelli ◽

F. Monaco ◽

A. Polci ◽

F. Russo ◽

...

Keyword(s):

West Nile Virus ◽

Northern Italy ◽

West Nile ◽

Lineage 2

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Evolutionary Dynamics of the Lineage 2 West Nile Virus That Caused the Largest European Epidemic: Italy 2011–2018

Viruses ◽

10.3390/v11090814 ◽

2019 ◽

Vol 11 (9) ◽

pp. 814 ◽

Cited By ~ 12

Author(s):

Carla Veo ◽

Carla della Ventura ◽

Ana Moreno ◽

Francesca Rovida ◽

Elena Percivalle ◽

...

Keyword(s):

West Nile Virus ◽

Evolutionary Dynamics ◽

Purifying Selection ◽

Genetic Distances ◽

Envelope Gene ◽

West Nile ◽

Clade B ◽

Sampling Locations ◽

History Of ◽

Lineage 2

Lineage 2 West Nile virus (WNV) caused a vast epidemic in Europe in 2018, with the highest incidence being recorded in Italy. To reconstruct the evolutionary dynamics and epidemiological history of the virus in Italy, 53 envelope gene and 26 complete genome sequences obtained from human and animal samples were characterised by means of next-generation sequencing. Phylogenetic analysis revealed two Italian strains originating between 2010 and 2012: clade A, which apparently became extinct in 2013–2014, and clade B, which was responsible for the 2018 epidemic. The mean genetic distances in clade B increased over time and with the distance between sampling locations. Bayesian birth-death and coalescent skyline plots of the clade B showed that the effective number of infections and the effective reproduction number (Re) increased between 2015 and 2018. Our data suggest that WNV-2 entered Italy in 2011 as a result of one or a few penetration events. Clade B differentiated mainly as a result of genetic drift and purifying selection, leading to the appearance of multiple locally circulating sub-clades for different times. Phylodynamic analysis showed a current expansion of the infection among reservoir birds and/or vectors.

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Whole genome sequencing and phylogenetic analysis of West Nile virus lineage 1 and lineage 2 from human cases of infection, Italy, August 2013

Eurosurveillance ◽

10.2807/1560-7917.es2013.18.38.20591 ◽

2013 ◽

Vol 18 (38) ◽

Cited By ~ 33

Author(s):

L Barzon ◽

M Pacenti ◽

E Franchin ◽

E Lavezzo ◽

G Masi ◽

...

Keyword(s):

West Nile Virus ◽

Northern Italy ◽

Viral Strain ◽

Genome Sequences ◽

West Nile ◽

Clinical Specimens ◽

North Eastern ◽

Large Outbreak ◽

Lineage 2 ◽

Unique Amino Acid

A human outbreak of West Nile virus (WNV) infection caused by WNV lineage 2 is ongoing in northern Italy. Analysis of six WNV genome sequences obtained from clinical specimens demonstrated similarities with strains circulating in central Europe and Greece and the presence of unique amino acid changes that identify a new viral strain. In addition, WNV lineage 1 Livenza, responsible for a large outbreak in north-eastern Italy in 2012, was fully sequenced from a blood donor during this 2013 outbreak.

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Faculty Opinions recommendation of Equine encephalomyelitis outbreak caused by a genetic lineage 2 West Nile virus in Hungary.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.10115956.10883054 ◽

2011 ◽

Author(s):

Lyle Petersen

Keyword(s):

West Nile Virus ◽

Genetic Lineage ◽

West Nile ◽

Lineage 2

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Epidemiology of West Nile Virus Infections in Humans, Italy, 2012–2020: A Summary of Available Evidences

Tropical Medicine and Infectious Disease ◽

10.3390/tropicalmed6020061 ◽

2021 ◽

Vol 6 (2) ◽

pp. 61

Author(s):

Matteo Riccò ◽

Simona Peruzzi ◽

Federica Balzarini

Keyword(s):

West Nile Virus ◽

Age Groups ◽

Invasive Disease ◽

Incidence Rates ◽

Annual Incidence ◽

Virus Infections ◽

West Nile ◽

Po River ◽

Air Temperatures ◽

Sex Risk

In Italy, human cases of West Nile virus (WNV) infection have been recorded since 2008, and seasonal outbreaks have occurred almost annually. In this study, we summarize available evidences on the epidemiology of WNV and West Nile neuro-invasive disease (WNND) in humans reported between 2012 and 2020. In total, 1145 WNV infection cases were diagnosed; of them 487 (42.5%) had WNND. A significant circulation of the pathogen was suggested by studies on blood donors, with annual incidence rates ranging from 1.353 (95% confidence intervals (95% CI) 0.279–3.953) to 19.069 cases per 100,000 specimens (95% CI 13.494–26.174). The annual incidence rates of WNND increased during the study period from 0.047 cases per 100,000 (95% CI 0.031–0.068) in 2012, to 0.074 cases per 100,000 (95% CI 0.054–0.099) in 2020, peaking to 0.377 cases per 100,000 (95% CI 0.330–0.429) in 2018. There were 60 deaths. Cases of WNND were clustered in Northern Italy, particularly in the Po River Valley, during the months of August (56.7%) and September (27.5%). Higher risk for WNND was reported in subjects of male sex (risk ratio (RR) 1.545, 95% CI 1.392–1.673 compared to females), and in older age groups (RR 24.46, 95% CI 15.61–38.32 for 65–74 y.o.; RR 43.7, 95% CI 28.33–67.41 for subjects older than 75 years), while main effectors were identified in average air temperatures (incidence rate ratio (IRR) 1.3219, 95% CI 1.0053–1.7383), population density (IRR 1.0004, 95% CI 1.0001–1.0008), and occurrence of cases in the nearby provinces (IRR 1.0442, 95% CI 1.0340–1.0545). In summary, an enhanced surveillance is vital for the early detection of human cases and the prompt implementation of response measures.

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