News

Biomedical Research Center SAS (BMC SAV) together with employees of 36 regional public health offices of the Slovak Republic, detected the West Nile virus and the Usutu virus in mosquitoes in several districts of Slovakia as part of the first nationwide monitoring, Thanks to this, it was possible to correctly diagnose patients infected with these viruses and test the donated blood.

“In the case of both mentioned viruses, we detected the most positive mosquitoes in August and September, and therefore, we have to expect cases of the disease especially in this period," explains Dr Viktória Čabanová from the BMC SAV Institute of Virology, who leads the project. "However, most infections are asymptomatic, and more serious forms occur only in a small percentage of those infected," she adds.

The Usutu virus was identified by scientists and experts from regional public health offices in mosquitoes in the districts of Košice, Dunajská Streda, Levice, Svidník, Prievidza, Nové Zámky, Veľký Krtíš, Senica and Humenné, and the West Nile virus in the districts of Nové Zámky and Košice.

Nationwide monitoring of the aforementioned viruses in mosquitoes was made possible by a new trapping method that saves time and money. Mosquito saliva was caught on specially designated cards. This large-scale method was used for the first time in Slovakia.

"Through monitoring, regional public health offices obtained information on whether there are mosquitoes infected with the given viruses in their territory, which can further transmit them to people. Subsequently, doctors have been warned to keep in mind these diseases when diagnosing. We diagnosed the disease caused by the Usutu virus in people in Slovakia for the first time in history,” explained Dr. Tatiana Červeňová, Chief Public Health Officer of the Slovak Republic.

A higher number of West Nile virus infections in Slovakia does not automatically mean that the number of infected people in the population is increasing. "However, we know that they are better diagnosed. This virus has been circulating here since the 1960s, but doctors need to know that it occurs in their district in order to take it into account when choosing a diagnosis," explains Dr Čabanová.

Both viruses are transmitted by transfusion, and because blood recipients are immunocompromised, infection with the more severe West Nile virus in particular often has a worse course than in the general population. In September, the National Transfusion Service of the Slovak Republic started testing the blood of donors for the presence of the West Nile virus in the Nové Zámky district based on the monitored data.

"We extended the testing to the entire Nitra region, Trnava and Bratislava regions, as soon as we received information about the first local transmission of the West Nile virus from a mosquito to a person in the Nitra region and the Dunajská Streda district. Thanks to the monitoring, we have time to procure tests and better prepare for the virus transmission from mosquito to human," said the medical director of the National Transfusion Service of the Slovak Republic, Dr Jana Rosochová.

Monitoring was carried out from July 1 to October 31, 2024, in 36 Slovak districts. The project will resume next year at the same time. In the future, this method can be used to track other viruses, and mosquito-borne parasites, as well as to monitor the presence of invasive mosquito species.

Basic information:

• West Nile virus - approximately 80 percent of WNV infections in humans are asymptomatic, others have flu-like symptoms. One to ten percent of those infected have more serious symptoms that may resemble encephalitis or meningitis. The problems mainly affect the elderly, children or people with impaired immunity.

• Usutu virus - the infection is in most cases asymptomatic or associated with mild symptoms, such as fever. Encephalitis or meningitis may rarely occur in immunocompromised and elderly patients.

• The Slovak Public Health Office has so far laboratory-confirmed eight cases of West Nile fever in Slovakia (2019, 2022, 2024). In five of them, local transmission on the territory of the Slovak Republic was confirmed, in the others import from abroad. As for diseases caused by the Usutu virus, two cases were confirmed in the laboratory in 2024, and the transmission took place on the territory of the Slovak Republic.

Text: Biomedical Research Center SAS, Slovak Public Health Office, Regional Public Health Office

Foto, mapa: Viktória Čabanová