On Friday, Florida Governor Rick Scott announced that the Zika virus is now being spread locally by mosquitoes in Miami Beach, Florida. This is considered an expansion of the outbreak, and the Centers for Disease Control (CDC) have issued a new travel advisory, warning pregnant women not to visit the area. Pregnant women who already live in Miami Beach have been instructed to stay indoors and guard as best they can from the virus.

The Zika virus has been known for more than half a century, but little effort has been made until recently to develop a vaccine, largely due to it being an affliction of impoverished countries. That the same conditions prevail in many parts of the United States, however, including in Florida, mean that the virus has found fresh ground.

Zika has been linked to birth defects in fetuses where pregnant women are infected with the virus. Thousands of infants throughout the Americas have recently been born with microcephaly, a brain defect which has been linked to Zika. Many women have chosen to terminate their pregnancies rather than give birth.

The virus is transmitted by mosquitoes; if one bites an infected person, it can then pass Zika to another person it bites. Medical officials have also discovered this year that it can be transmitted sexually. Hundreds of cases have already been discovered in the United States in people who had traveled to areas where Zika had been found, or had sexual contact with such persons.

The first cases of mosquito-borne Zika in the continental United States were discovered by the Florida Department of Health (FDOH) earlier this month in what was initially a one-square-mile zone of Miami, just west across Biscayne Bay from Miami Beach.

The new area that has been added to the warning area is a 1.5-square-mile area in Miami Beach, between the beach itself and the Intracoastal Waterway—a space that contains the densely-packed South Beach tourist district. Within this warning area is the Miami Beach Convention Center, a 45,000-person capacity venue that holds a variety of sporting events and other happenings throughout the year.

As of Friday, health officials reported that at least five people have been infected with Zika by mosquitoes in this area, two of whom reside there. The other three were visiting from Texas, New York, and Taiwan, respectively.

The CDC issued a new travel advisory on Friday afternoon, saying pregnant women should avoid the new warning zone in Miami Beach. This is the first time since the CDC was founded in 1946 that it has issued such a warning within the United States. They also advised that pregnant women and their sexual partners living in the affected area should take extra precautions to protect themselves from mosquitoes, including wearing repellent.

Zika prevention kits that include repellant, condoms, and mosquito nets have been given to pregnant women in the affected areas. Obstetricians have been instructed to assess every pregnant patient at each prenatal visit for exposure to Zika.

Dr. Aaron Elkin, an obstetrician in the area, reported to the New York Times that every woman coming in for prenatal care wanted Zika testing. “You can’t say no to them,” he related. “They’re very frightened. I’m doing 15 tests a day.” Some patients are considering leaving the state, at least for the durations of their pregnancies.

One of the new concerns, now that the mosquitoes have been found in a popular tourist destination, is that people will bring the virus home with them. According to statistics, Miami Beach hosts 35 percent of the approximately 10 million tourists who visit Greater Miami every year. Nearly half of these come from outside of the United States. The three infected individuals visiting from Texas, New York, and Taiwan had already returned home.

Another possible channel for international exposure is through PortMiami, the leading cruise-line port in the world. Some cruise lines, as well as airlines like JetBlue, have begun offering refunds and rescheduling to customers who have concerns about visiting Zika-affected areas, including Miami.

Other barriers to controlling the spread of the virus are the presence of high-rise buildings that prevent low-flying planes from spraying specialized insecticide over the area, as they have done on the other side of the bay, as well as the prevalence of clothing used at the beach that does little to protect against mosquito bites.

Another important concern, especially for people like Governor Scott, is the negative economic impact the Zika outbreak will have on tourism in Florida.

“Tourism is a driving force of our economy,” he stated on Friday. “This industry has the full support of our state in the fight against the Zika virus. We want to do all we can to ensure Florida remains safe for businesses and our families.” On Thursday, Scott’s office denied the presence of Zika-carrying mosquitoes in Miami Beach, and he has since been accused of trying to obscure evidence in order to protect the state’s $82 billion tourism industry.

To date, Zika has officially spread to 70 countries. There have been a confirmed number of 2,200 cases in the United States and more than 8,000 in US territories, mostly in Puerto Rico. The CDC is currently tracking the health of 529 pregnant women within the US and nearly 700 within the territories who have been afflicted with the virus. The number of locally-acquired cases of Zika in Florida has now reached a total of 36.

CDC Director Tom Frieden has stated that “there are undoubtedly more infections that we are not aware of right now” because roughly 80 percent of those infected see no symptoms. “We can’t predict how long this will continue, but we do know that it will be difficult to control.” Frieden has stated that the mosquito, Aedes aegypti, is very difficult to kill, dubbing it “the cockroach of mosquitoes.”

The Obama administration has asked for $1.9 billion to help fight Zika, but Congress has not come to a decision, leaving for a summer recess without allocating any funds. The administration recently reallocated $81 million from other programs, but health officials say that there will be no money left by the end of September.