OKLAHOMA CITY (AP) -- The number of human cases of West Nile Virus has leveled off in Oklahoma while the number in horses has risen sharply in the past two months. The state Health Department on Thursday reported 176 cases and 12 deaths this year due to the virus -- an increase of one case since Tuesday and up by six from two weeks ago. State epidemiologist Dr. Kristy Bradley says a recent light freeze and cooler temperatures have slowed the activity of the mosquito that carries the virus. While the increase in human cases has slowed -- the number of cases in horses has jumped from two at the end of August to 39. State veterinarian Dr. Rod Hall says the cause isn't clear and encourages horse owners to vaccinate their animals.