1. Mercedes's initial CSF sample was negative for WNV-specific IgM because it takes time for the body to produce antibodies in response to the infection. In the early stages of the infection, the body may not have produced sufficient levels of WNV-specific IgM antibodies to be detected in the CSF sample.
2. Mercedes must be monitored for changes in intracranial pressure and seizures because West Nile Virus can cause inflammation and damage to the brain. Increased intracranial pressure can be a result of inflammation and swelling in the brain, which can lead to detrimental effects if not managed properly. Seizures can also occur as a result of the infection's impact on the brain, and monitoring for them allows for prompt medical intervention if necessary.