Mosquitoes carrying West Nile fever have been identified in the heavily populated Gush Dan area of central Israel for the first time this summer.
The Environmental Protection Ministry on Wednesday again warned coronavirus sufferers to take particular care.
The Tel Aviv and Ramat Gan municipalities have been instructed to increase monitoring and, where necessary, undertake pest control.
Diseased insects have already been found in the north of the country in and around the Kishon Stream in the Mount Gilboa area, and in the communities of Yotvata, Ketura, Eliphaz and Grofit in the Arava Desert in the south.
West Nile fever is a zoonotic disease, meaning that it originates in animals and is transmitted to humans. It is caused by a virus found mainly in birds, and is spread to humans through mosquito bites.
There is no vaccine against the disease.
In most cases, bites cause a mild, flu-like illness that goes away on its own. Symptoms include fever, headache, weakness, joint and muscle pain, conjunctivitis, rash and sometimes nausea and diarrhea.
But in 2018, three Israelis died from the disease.
Last year, according to Health Ministry figures, 32 human cases of West Nile fever were reported in 27 localities, infected animals were found in four locations, and infected mosquitoes were spotted in 34 places throughout the country.
The ministry has set out a list of steps the public should take to reduce exposure to West Nile fever.