An unvaccinated child has contracted the contagious measles virus in Pinellas County, according to the Florida Department of Health, which said Monday it is investigating the case.

It was unclear how the child contracted the virus, according to the health department. But local officials are working to identify and notify people who were potentially exposed. The child was diagnosed at Morton Plant Hospital in Clearwater.

The case is expected to be isolated, and no additional precautions are being taken in local schools or other public places. Meanwhile, the health department encouraged all residents and visitors who have not been immunized to get vaccinated.

Measles is a virus that spreads in the air when an infected person breathes, coughs or sneezes. The first symptoms are a fever that could spike to 105 degrees, a persistent cough, runny nose, and red, watery eyes. A blotchy rash can spread from the head to the feet, according to the health department.

Measles, if untreated, can become severe, especially in young children and people with compromised immune systems. It also is highly contagious — so much so that if one person has it, 90 percent of the unvaccinated people close to that person will get it.

The virus was once eradicated in the U.S., thanks to immunizations, but a recent shift in views against routine vaccinations by some parent groups has contributed to its return. The antivaccination movement is fueled by parents who believe there is a link between vaccines and autism, though no such link has been proven, or who see more harm than good resulting from having their children vaccinated.

While there are no outbreaks reported in Florida, two residents and one visitor were confirmed to have measles after trips to Brazil and France last month, according to the health department. So far this year, four Florida residents and three visitors were in the state while considered "infectious."

As of July, 404 people in Florida were identified as being exposed to measles. The Centers for Disease Control and Prevention reports 107 cases of measles nationwide so far this year. Officials reported 118 cases last year and 86 cases in 2016.

The Florida Department of Health and the CDC recommend vaccination as the best way to protect against measles. Two doses of the measles, mumps, rubella (MMR) vaccine is recommended for children, with the first dose at age 12-15 months and the second at four-to-six years. Adults should be vaccinated with at least one dose of the MMR vaccine, with a second dose recommended for those at higher risk, such as international travelers or health care workers.

"We are continuing to investigate, but we would like families to know that their children could be exposed to diseases like measles anywhere and unless they're protected with vaccination they are risking potentially serious health effects for their child," said Dr. Ulyee Choe, director of the health department in Pinellas County and an infectious disease specialist. "We encourage all parents to fully vaccinate their children to protect them from diseases like measles."

RELATED: Chicken pox cases spike at Clearwater's Plumb Elementary; unvaccinated kids told to stay home

In 2016, health department officials investigated an outbreak of chicken pox at Plumb Elementary in Clearwater, which kept 18 unvaccinated children home from school for 21 days. The chicken pox vaccine is required for all children who enroll in Florida public schools. Students can be exempted for medical or religious reasons.

Those who are not vaccinated but are exposed to measles should avoid public places, like school and work, for up to 21 days. The health department urges anyone experiencing symptoms of measles to see their health care provider and report suspected cases.

Contact Justine Griffin at jgriffin@tampabay.com or (727) 893-8467. Follow @SunBizGriffin.