(Philadelphia) -- The number of people infected by the West Nile virus has increased sharply in Pennsylvania this week.
The state Department of Environmental Protection says four cases had been recorded in the Philadelphia region this week, bringing the total to 11 cases in the commonwealth this year.
The new cases involve a Philadelphia man and woman and two men from Montgomery County.
Earlier this month, a Bucks County man had died after becoming infected with the virus.
The virus is transmitted to humans by mosquitoes that can pick it up from infected birds. It can lead to encephalitis, a dangerous inflammation of the brain.
Older people and those with weakened immune systems are at greatest risk.
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