Since the beginning of the year, confirmed cases of West Nile Virus (WNV) infection in humans in Italy have risen to 173, up from 89 on July 31, with 11 deaths.
Of the confirmed cases, 72 were neuroinvasive (2 in Piedmont, 2 in Lombardy, 4 in Veneto, 1 in Friuli-Venezia Giulia, 2 in Emilia-Romagna, 37 in Lazio, 21 in Campania, 1 in Basilicata, 1 in Sardinia), 14 asymptomatic cases were identified in blood donors, 85 cases of fever, 1 asymptomatic case, and 1 symptomatic case.
Of the confirmed cases, 11 deaths have been reported (1 in Piedmont, 4 in Lazio, 6 in Campania). The case fatality rate, calculated for the neuroinvasive forms reported to date, is 15% (20% in 2018, 14% in 2024).
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"The situation is being closely monitored by all relevant institutions, both centrally and locally. At the moment, no particular alarm signals are emerging," emphasizes Anna Teresa Palamara, director of the ISS's infectious diseases department. "We emphasize the importance of prevention measures, both those aimed at combating mosquito breeding and those aimed at protecting against bites. We also remind everyone, especially the frail or elderly, to contact their doctor if they develop a fever."
West Nile fever is a disease caused by the West Nile virus (WNV), a virus of the Flaviviridae family first isolated in 1937 in Uganda, in the West Nile district (hence its name). The virus is widespread in Africa, Western Asia, Europe, Australia, and the Americas.
The virus's reservoirs are wild birds and mosquitoes (most commonly of the Culex genus), whose bites are the primary means of transmission to humans. Other documented means of infection, although much rarer, are organ transplants, blood transfusions, and mother-to-child transmission during pregnancy. West Nile fever is not transmitted from person to person through contact with infected individuals. The virus also infects other mammals, especially horses, but in some cases also dogs, cats, rabbits, and others. In Italy, for several years now, several dozen cases of West Nile fever have been reported during the summer months (up to several hundred in the years with the highest incidence), transmitted by mosquito bites. No cases of transmission by transfusion or transplant have ever been documented, thanks in part to the specific measures implemented each year.
The incubation period from the moment of being bitten by an infected mosquito varies between 2 and 14 days, but can be up to 21 days in individuals with immune system deficiencies. Most infected people show no symptoms. Among symptomatic cases, approximately 20% present with symptoms such as fever, headache, nausea, vomiting, swollen lymph nodes, and skin reactions. These symptoms can last a few days, or in rare cases, a few weeks, and can vary greatly depending on the person's age. A mild fever is more common in children, while in young people, symptoms are characterized by a moderately high fever, red eyes, headache, and muscle aches. In the elderly and frail, for example due to previous illnesses, symptoms can be more severe. The most severe symptoms occur in an average of less than 1% of infected people (1 in 150) and include high fever, severe headache, muscle weakness, disorientation, tremors, vision changes, numbness, convulsions, and even paralysis and coma. Some neurological effects can be permanent. In the most severe cases (about 1 in 1,000), the virus can cause fatal encephalitis.