For the first time in nearly two decades, mosquitoes found in Southeast Texas have tested positive for the deadly St. Louis encephalitis virus. "The curious thing about St. Louis (encephalitis) is that it pops up in outbreaks and then it disappears," said Robert Tesh, a pathology professor at UTMB. A healthy young person diagnosed with the virus might experience a mild fever or a headache. "You probably wouldn't even go to the doctor," Tesh said. The elderly and those with immune system disorders are at higher risk and could suffer from more severe symptoms. "A sporadic case here and there shouldn't cause a public health problem," Tesh said.