Italy's West Nile Virus Outbreak Intensifies

A rapid increase in neuroinvasive West Nile virus (WNV) infections in humans have been reported in northern Italy, in contrast to other EU/EEA countries, during the summer of 2022. Strains of WNV lineage 1 and 2 are co-circulating

Italy records, on average, about 60 locally acquired human cases every year, mainly in the country's north. 

EuroSurveillance published a Rapid communication on September 8, 2022, confirming the first detection of WNV circulation in 2022 occurred in early June in mosquitoes and birds, with human cases detected beginning June 19 and rapidly increasing in July 2022.

A total of 182 confirmed human infections had onset or, if unavailable, diagnoses up to July 31, including 105 (57.7%) West Nile neuro-invasive disease (WNND) cases, of which 13 were fatal (case fatality rate (CFR): 12.4%), 54 West Nile fever cases, and 21 asymptomatic infections among blood donors and two patients with unspecified symptoms.

The male: female ratio of those infections was about 2:1.

For comparison, during the 2018 epidemic year, Italy reported 162 human confirmed cases with onset or diagnosis up to July 31.

Raising awareness among clinicians can also encourage considering WNV among differential diagnoses in people with fever and/or neuroinvasive disease living in or returning from endemic areas.

As of September 14, 2022, the U.S. FDA had not approved any West Nile virus vaccine.

And the U.S. CDC has not issued a related travel alert for Italy.