CHICAGO/TAMPA, Fla. (Reuters) - Florida officials on Tuesday announced the first case of Zika transmitted by mosquitoes in Pinellas County, located some 265 miles (425 km) from Miami, where the first locally transmitted U.S. cases were reported.

Aedes aegypti mosquitoes are seen inside Oxitec laboratory in Campinas, Brazil, February 2, 2016. REUTERS/Paulo Whitaker/File Photo

Steve Huard, acting spokesman for Florida Department of Health in Pinellas County, said the case involves a woman without a significant travel history, indicating the virus was contracted locally.

He did not know the timeline on the case, only that it had been confirmed within the past day. He did not have any more details on the patient’s illness.

“At this point, it’s a single case. It’s a one-off,” Huard said. “We don’t know where it originated, and we are doing appropriate testing and medical surveillance.”

Florida Governor Rick Scott said the state department of health has begun door-to-door outreach in Pinellas County, testing individuals to find other cases.

Pinellas County is home to St. Petersburg, Clearwater and a number of Gulf Coast beaches that are popular tourist destinations.

Scott said the health department and Pinellas County Mosquito Control have begun “aggressive spraying and mosquito abatement efforts,” and he said any pregnant woman who wants a free Zika test or a Zika prevention kit should contact the health department.

The Zika virus was first detected in Brazil last year and has since spread across the Americas. The virus poses a risk to pregnant women because it can cause severe birth defects. It has been linked to more than 1,800 cases of microcephaly in Brazil.

Federal health officials on Friday warned pregnant women not to travel to Miami Beach after Florida confirmed that the mosquito-borne Zika virus was active in the popular tourist destination, becoming the second area in Miami to be affected after Wynwood.

Mara Gambineri, a spokeswoman for the Florida Department of Health said the department believes ongoing local transmission is only occurring in the small areas identified in Miami-Dade County.

On Tuesday, Florida announced four new cases of Zika in the Wynwood neighborhood, where officials have been aggressively spraying for the mosquitoes that carry the virus for weeks. Florida has so far reported 42 cases of locally transmitted Zika.

Gambineri said in an email the cases of individuals in Wynwood experienced Zika symptoms in mid-July, prior to the start of an aerial spraying campaign. Gambineri said the cases were only announced today because the individuals required antibody testing to rule out other mosquito-borne illness, such as dengue and Chikungunya.

CLOSELY MONITORING NEW CASES

In a conference call on Friday, Dr. Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention, said the CDC does expect to see occasional cases of local transmission, which is what experts have seen with outbreaks of dengue and Chikungunya.

In those outbreaks, for every 9 or so one-off cases, there was one new cluster of local mosquito-borne transmission, but he said, “The vast majority of local transmissions hit a dead end after one or two people in one household.”

Frieden said the CDC is closely monitoring new cases in the Wynwood neighborhood to see whether their mosquito control efforts - which have included aerial spraying of pesticides to kill adult mosquitoes and mosquito larvae - are working.

Mosquito control experts in Pinellas County are not planning the type of aerial spraying campaign underway in Miami-Dade County. Local officials said they believe ground-level efforts will be most effective against the type of mosquito that transmits Zika, which can breed in small containers.

Rob Krueger, an entomology and education support specialist with Pinellas County Mosquito Control, compared aerial spraying to dropping golf balls on a football field. While chemical droplets may get close to the mosquito habitat, there is no way to know that every possible breeding spot has been reached through a diffuse, overhead approach.

“Our method is strictly boots-on-the-ground, and going door to door to make sure that we can find every Aedes aegypti mosquito that is out there and eradicate it,” Krueger said.

He said mosquito control districts in Florida have flexibility to use the approach and chemical agents best suited for the local population and financial resources. Pinellas, which is Florida’s most densely developed county, does not typically use aerial spray products against this type of mosquito.

Krueger said there is no “magic bullet” for eradicating Aedes aegypti. What it is going to take is “going door to door, fixing it as we go.”

Dr. Amesh Adalja, an infectious diseases expert at the University of Pittsburgh Medical Center, said Florida needs to make it clear that “anywhere these mosquitoes are present is at risk.”

Adalja said while knowing the exact area of transmission is important for issuing travel warnings to pregnant women, he said the entire state needs to be vigilant.

Adalja expects multiple counties in Florida will be affected, as well as areas in Texas and Louisiana, though these outbreaks will be limited to discreet areas.