This study will test whether plasma containing high levels of neturalizing antibodies against West Nile virus (WNV) can help people hospitalized with severe West Nile fever recover faster and avoid serious complications. West Nile virus is spread by mosquitoes and can cause mild flu-like symptoms or, in severe cases, brain infections. Currently, there is no specific medication to treat the infection, and doctors primarily provide supportive care. In this study, patients who are sick enough to require hospitalization will receive plasma donated by people who have recovered from West Nile virus and developed high titer neutralizing antibodies against the disease. Researchers will closely monitor these patients to see how quickly their symptoms improve and whether the plasma helps reduce the risk of death or shorten hospital stays. To evaluate how well the plasma works, researchers will compare these patients to others who were infected in the past for West Nile virus but did not receive plasma. The study will also examine whether the plasma is safe to use and whether it causes any side effects. Through this research, scientists hope to determine if antibody-rich plasma could become a helpful treatment option for people with severe West Nile virus infections.