West Nile encephalitis is a brain infection caused by West Nile Virus, previously only found in Africa, Eastern Europe, and West Asia. Encephalitis is an inflammation of the brain and can be caused by head injury, bacterial infections, or most commonly, viral infections. West Nile encephalitis cases occur primarily in the late summer or early fall. People can get infected from the bite of certain kinds of mosquitoes infected with the virus.
Mosquitoes get it when they bite, or take a blood meal, from birds infected with West Nile virus.
Those mosquitoes then transmit the virus to people and other animals when biting to take blood. People over 50 years of age have the highest risk of developing severe illness because as we age, our bodies have a harder time fighting off disease. Horses become infected with West Nile virus after being bitten by an infected mosquito. There is no evidence that horses can transmit the West Nile virus to other horses, birds or people. In horses that do become clinically ill, the virus infects the central nervous system and causes symptoms of encephalitis.