Greece's health ministry said on Tuesday it was stepping up the fight against West Nile virus which has killed three people since the beginning of the month.
Some 47 people were diagnosed with the virus on Monday including 11 new cases discovered over the weekend, according to a statement from the Centre for the Control and Prevention of Diseases (KEELPNO).
Of this total, 45 patients have been diagnosed with encephalitis - an inflammation of the brain caused by the virus - of whom three elderly patients, also suffering from unrelated diseases, died.
According to KEELPO, seven of the 28 people hospitalised on Monday are in intensive care.
The virus, transmitted through infected mosquito bites, has so far affected populations in Macedonia, in a zone stretching from Larissa to the northern city of Salonica, in close proximity to lakes and rivers.
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The health ministry has ordered that efforts to spread insecticides in the region be intensified, targeting areas where contamination is highest. A campaign to inform the public will also be launched.
KEELPNO's Doctor Doritsa Bakka said the virus has been found in the past in Greece but had never before caused encephalitis.
She said the spread of the disease had been encouraged by a hot and wet summer, an ideal breeding ground for mosquitos.
