Five cases of West Nile virus have been reported since early July in a seaside suburb of Athens, the Greek centre for disease control and prevention (Keelpno) said Friday.
Since July 7, three 60 year-olds, one 40 year-old and an 18 year-old man have been diagnosed with the mosquito-borne disease, said the centre.
While the first victims were successfully treated, the latest three had been hospitalised for symptoms "affecting the central nervous system," Keelpno added.
The cases mark a reappearance of the virus in Greece after an outbreak in 2011 that killed nine people, having infected 101, said a statement on the Keelpno website. The average age of those infected was 70.
The virus had thus far mainly surfaced in the region of Macedonia, near rivers and lakes.
Cases also cropped up last year in the region of the capital, with infections in the eastern agricultural area and western industrial zone.
The virus can cause symptoms similar to those of the flu, but in extreme cases it can result in tremors, fever, comas and a lethal swelling of the brain tissue known as encephalitis. It can also cause meningitis.
First discovered in Uganda in 1937, the virus is carried by birds and spread to humans by mosquitoes. It is indigenous to Africa, Asia, Europe and Australia.