Mosquitos become infected with the West Niles virus by feeding off of infected birds.
The West Nile virus is an arbovirus. This means that it is a virus that is transmitted via arthropods, such as mosquitos, ticks, fleas, lice, or sand flies.
People become infected with the West Niles virus by being bitten by infected mosquitos. Most people, 70-80%, do not develop symptoms. The West Nile virus causes febrile illness in about 1 out of every 5 people. This may result in fevers, body aches, joint pains, headaches, vomiting, or diarrhea. About 1% of people that become infected with the West Nile virus experience severe symptoms such as encephalitis or meningitis. Encephalitis causes the brain to inflame. Meningitis results in the inflammation of the spinal cord and/or brain.