Two pensioners, both 80, from the Attica region in southern Greece, became the first fatalities on Wednesday, with 12 more people hospitalised on the same day.
All showed symptoms in the central nervous system, and four have been admitted into intensive care.
Symptoms can include encephalitis, meningitis, and acute relaxed paralysis.
At least 55 outbreaks have been reported in the EU between July 27 and August 3, according to the European Centre for Disease Prevention and Control (ECDPC).
West Nile Virus doesn’t show any symptoms in 80 percent of infected people, and if left untreated it can lead to West Nile fever or severe West Nile disease, according to the World Health Organisation.
Symptoms of the severe disease that include headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis.
People over the age of 50 are at the highest risk for getting severely ill when infected by the mosquito-borne virus.
Typically 20 percent of people report having mild symptoms and less than one percent suffer severe symptoms in the central nervous system, according to the the Hellenic Center for Disease Control and Prevention (HDCDP).
Earlier this month, a 79-year-old man died in Verona after contacting the virus.
Authorities in the northern Italian region of Veneto had diagnosed 19 with the mosquito-borne illness.
In the town of Fossalta di Piave, also in the Veneto region, the mayor has ordered a “massive disinfestation” of the area after a 53-year-old woman tested positive for the virus.
She sought medical help suffering from a headache and joint pains as well as a rash all over her body.
Announcing the decontamination operation, mayor Massimo Sensini said: “Weaker subjects, who could be more exposed to the problem, can rest assured. I still invite the population to protect themselves from mosquito bites, particularly outside houses, with suitable repellents and clothing.”
Since the beginning of the transmission season 111 human cases have been reported in EU Member States and surrounding states.
Outbreaks have been reported in Hungary, Romania and Serbia, according to the ECDPC.
The virus is transmitted when people are bit by infected mosquitos. The mosquitos get infected mainly by wild birds.
There is currently no vaccination available for humans for the West Nile virus.
Treatment for patients hospitalisation, intravenous fluids, respiratory support, and prevention of secondary infections.