What does West Nile Virus do?

I know that the virus comes from Mosquito bites. But what does the virus do? Attack the brain? Also what does the West Nile Fever attack? Muscles? Brain?
Please Help

West Nile Virus is a flavivirus commonly found in Africa, West Asia, and the Middle East. It is closely related to St. Louis encephalitis virus which is also found in the United States. The virus can infect humans, birds, mosquitoes, horses and some other mammals.

The most severe type of disease due to a person being infected with West Nile virus is sometimes called 鈥渘euroinvasive disease鈥?because it affects a person鈥檚 nervous system. Specific types of neuroinvasive disease include: West Nile encephalitis, West Nile meningitis or West Nile meningoencephalitis. Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord, and meningoencephalitis refers to inflammation of the brain and the membrane surrounding it.
The symptoms of severe disease include; headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, muscle weakness, and paralysis. It is estimated that approximately 1 in 150 persons infected with the West Nile virus will develop a more severe form of disease. Serious illness can occur in people of any age, however people over age 50 and some immunocompromised persons (for example, transplant patients) are at the highest risk for getting severely ill when infected with WNV.
West Nile Fever is another type of illness that can occur in people who become infected with the virus. It is characterized by fever, headache, tiredness, aches and sometimes rash. Although the illness can be as short as a few days, even healthy people have been sick for several weeks.

Most people (about 4 out of 5) who are infected with West Nile virus will not develop any type of illness (an asymptomatic infection), however you cannot know ahead of time if you'll get sick or not when infected.