Florida's caseload of Zika spread by Miami mosquitoes has risen to 25, and U.S. health officials continue to warn pregnant women to avoid the infection zone despite the governor's assurances that the area of concern is shrinking.

Florida's Department of Health says active transmission has been only happening in a 1-square-mile area encompassing Miami's Wynwood arts district.

Scott's office also announced that the health department has declared four blocks in the southwest corner of Wynwood to be clear of infections as preventative measures continue, in addition to another 10-block section cleared last week.

The U.S. Centers for Disease Control and Prevention, however, still advises pregnant women to avoid the entire neighborhood. "All I can say is the travel advisory is still in effect," CDC spokesman Tom Skinner said.

Zika is a mosquito-borne virus that only causes mild, flu-like symptoms in most people. But it can cause severe brain-related defects, including disastrously small heads, if women are infected during pregnancy.

Back-to-school day is Aug. 22 in Miami, and while students returning to class in Wynwood will be allowed to wear pants and long-sleeved shirts that don't match their school uniforms, they still can't bring mosquito repellent to campus.

Miami-Dade County Public Schools Superintendent Alberto Carvalho said at a school board meeting Wednesday that "aggressive application" of repellent should be done at home, not at school where some students may be allergic to the spray. Some 4,000 students attend six schools in the Wynwood arts district.

The Miami Herald reports that state health workers will be stationed at each school to check for mosquito breeding sites and provide parents with repellent.

Aerial spraying of pesticides targeting adult mosquitoes was scheduled Friday over Wynwood as well as surrounding areas, and tablets of larvae-eating bacteria are being dropped into storm drains throughout Miami-Dade County.