West Nile virus, spread by mosquitoes, has caused four people to take sick and five more suspected cases since late spring, the Health Ministry said on Tuesday. All are in good condition.Back in 2000, there were 417 confirmed cases in Israel, with 326 hospitalizations.Thirty-three of these people died.Researchers believe West Nile virus is spread when a mosquito bites an infected bird and then bites a person.This year, the number of cases has been smaller than usual, the ministry said, as June was among the coolest in 25 years and not hospitable to the insects. Therefore, the mosquito season may continue through the end of autumn this year, it said.The main types of mosquitoes to spread the virus are Culex Pipiens and Culex perexiguus.Symptoms of the infection are like those of a mild flu and include fever, headaches, weakness, joint and muscle pain, rashes, conjunctivitis around the eyes, and sometimes diarrhea and nausea. Rare complications include meningitis and encephalitis. Between the mosquito bite and the development of symptoms, anywhere from three to 21 days pass, but the average is three to 15.Prevention is the best way to cope with West Nile fever. There is no vaccine. Mosquitoes are most active in the evening and at night, so people with weak immune systems, including the elderly, should protect themselves during these hours. Install screens on windows; spraying can be effective but only when performed by a licensed professional.