Heard about a virus that causes swelling of the brain, what is it?

More than one. A class of neurological infections by different viruses, known as viral encephalitides, exists. Cases in this category often induce cerebral edema, which is the medical term for brain swelling. Treatment may or may not be successful. Cerebral edema can result in permanent damage or death. Different viruses are variably infectious, some much more than others.