West Nile: ISS counts 312 confirmed cases and 13 deaths in the 2026 season
The fourth report of the integrated surveillance, updated to 19 August, records an increase compared with the previous week. For two other arboviral diseases, national data are no longer published on the Institute's online data dashboard.
Confirmed human West Nile virus infections in Italy number 312. The figure appears in the fourth seasonal bulletin on integrated West Nile and Usutu surveillance, with data updated to 19 August 2026. The document is produced by the Department of Infectious Diseases of the Istituto Superiore di Sanità and the Center for Exotic Disease Studies of the Istituto Zooprofilattico Sperimentale dell’Abruzzo e del Molise, in collaboration with the Ministry of Health; it is published on EpiCentro.
The composition of the data
The 312 confirmed cases are not all clinically equivalent, and this distinction is the first element to bear in mind when reading the total.
| Category | Cases |
|---|---|
| Neuroinvasive form (of which 1 imported) | 156 |
| Fever cases | 115 |
| Asymptomatic cases identified among blood donors | 40 |
| Deaths reported (of which 1 in an imported case) | 13 |
The proportion of asymptomatic cases emerging from blood donation screening indicates that the overall count also depends on the intensity of case-finding efforts, and not solely on virus circulation.
Comparison with the previous report, updated to 12 August 2026 and available in bulletin no. 3, shows the direction of the season: at that time confirmed cases stood at 226 and reported deaths at 7. Over one week of monitoring, the case count therefore rose by 86 and the death count by 6. Molecular analyses have confirmed the circulation of lineages 1 and 2 of the virus.
The data that are no longer visible
On the front of other arboviral diseases, the national source has reduced what it makes public. In the current version of the online arbovirus data dashboard, the Istituto Superiore di Sanità does not show figures relating to TBE and Toscana virus cases: the reason given concerns revisions required by compliance with personal data protection regulations. The methodological notes can be consulted in the arbovirus bulletins section.
For Toscana virus, transmitted by sandflies, the most recent picture available therefore comes from scientific literature. A study on Italian surveillance recorded 607 confirmed autochthonous neuro-invasive cases between 2016 and 2023, of which 276 were concentrated in the 2022-2023 two-year period, with an incidence roughly 2.6 times higher than in the 2016-2021 period. The limits of this measure must be stated: this is surveillance data, that is, only confirmed and reported cases, not an estimate of infections in the population; the figure concerns neuro-invasive forms and not the totality of infections, which in most cases are asymptomatic or present with fever, headache and general malaise; the available source does not report details of the collection method or any conflicts of interest declared by the authors. An increase in confirmed cases within a surveillance system may also depend on an increase in tests performed.
On seasonality, virologist Fabrizio Pregliasco, quoted in an article by Il Tirreno, states: “The peak in cases is recorded in August”.
What we do not know
The West Nile report does not allow one to derive from it the regional distribution of the 312 cases or the trend compared with previous seasons. For TBE and Toscana virus cases, no date is given for the resumption of national data publication on the online dashboard. National arbovirus surveillance remains coordinated by the ISS, with periodic bulletins dedicated to Chikungunya, Dengue, Zika, TBE and Toscana virus neuro-invasive infections.
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