West Nile encephalitis is caused by West Nile virus, a flavivirus previously only found in Africa, Eastern Europe and West Asia. Encephalitis means an inflammation of the brain and can be caused by either head injury, bacterial infections, or, most commonly, viral infections. People are infected from the bite of a Northern house mosquito that is infected with the virus.
Mosquitoes get it when they bite, or take a blood meal, from birds infected with West Nile.
Those mosquitoes then transmit the virus to people and animals when taking a blood meal. 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. Mild infections are common and include fever, headache, and body aches, often with skin rash and swollen lymph glands. Headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions, and paralysis mark more severe infection. There is no specific therapy.