What is West Nile virus?
West Nile virus is a type of virus that is spread by mosquitoes. The infection it causes may be so mild that people don't even know they have it. But in rare cases, West Nile leads to severe illness that affects the brain or spinal cord. People older than 50 are at the highest risk for serious problems from West Nile.
Most people fully recover from West Nile. But some people who get a severe infection have permanent problems such as seizures, memory loss, and brain damage. A few people die from it.
How is West Nile virus spread?
Most often, mosquitoes spread the virus by biting birds infected with the virus and then biting people.
Mosquitoes can also spread the virus to other animals, such as horses. But you can't get West Nile from these animals or from touching or kissing an infected person.
West Nile can spread through an organ transplant or a blood transfusion. That rarely happens in the United States, though, because all donated blood is screened to see if the virus is present.
Some evidence suggests that West Nile can spread from a mom to her baby during pregnancy, at birth, or through breast milk. But the U.S. Centers for Disease Control and Prevention still recommends that women breast-feed. Breast-feeding has many benefits, and the risk of spreading the virus to babies seems to be very low.