A fourth person has died after contracting West Nile virus, as the number of infections continues to rise, according to the Dutch National Institute for Public Health and the Environment (RIVM). The agency said this latest individual was infected through a blood transfusion by an infected donor. It is, however, unclear if the virus was the cause of the death or a contributing factor.

Additionally, 10 people have recently tested positive for the virus, bringing the total number of cases to 28. Almost all of them reportedly got the infection following mosquito bites in Overijssel, Utrecht, Gelderland, Noord-Holland, Noord-Brabant, and Zuid-Holland.

After the donor that infected the latest victim tested possible for the West Nile virus, Blood Bank Sanquin blocked the donation unit, so no one else received the infected blood.

West Nile virus originated in birds and can be passed along to humans by mosquitos. When infected, the people can develop flu-like symptoms. Encephalitis, meningitis, or a polio-like disease can also occur in rarer cases.

According to the RIVM, most people notice little or almost nothing after being infected. Apart from the humans, West Nile virus has also been confirmed in 61 wild birds and 30 horses. Overall, the agency estimates that several thousand people in the Netherlands have contracted the virus so far.