MERCED  (AP) — A Merced County woman has become the fourth person in the state to die of West Nile virus this year.

Health officials said Thursday that the 86-year-old woman died this month after becoming infected in August.

There have been three other West Nile virus-related deaths in the state in 2012: an elderly Fresno County woman, an 88-year-old Kern County woman and an 85-year-old Sacramento County man.

State officials say dozens of other people have been infected with the virus, but have survived. Ten horses and more than 1,000 dead birds have also tested positive for the infection.

The virus is spread by mosquitoes. One out of every 150 infected people develop severe symptoms, including neck stiffness, disorientation, coma and paralysis.