5 deaths reported due to West Nile virus
Another 42 people fell ill due to the mosquito-borne illness, with the majority of cases reported on the Peloponnesian peninsula.
Post-mortem lab tests had confirmed the causes of death, with all five victims over the age of 70.
The number of infected patients could be even higher, as most reported no or only innocuous symptoms, such as headaches and sore limbs, doctors said in an interview on national radio.
Residents were advised to use plug-in repellents or ointments against insects.
According to the Centre for Travel Medicine in Dusseldorf, Germany, West Nile virus was first detected in Greece in 2010.
Infections have occurred regularly since, although there were no reported cases in 2015 or 2016.
West Nile virus is a viral infection similar to the flu, while it had long been localised to the tropics and subtropics, cases have been reported in North America since the 1990s.
Symptoms, which include muscle pain, swollen lymph nodes and fever, tend to appear three to six days after infection.
About a third of patients experience skin rashes on their chest, back and arms, however, in rare cases, the virus can lead to an inflammation of the brain, and can be fatal.
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