By Dennis Thompson

HealthDay Reporter

(HealthDay)

FRIDAY, Aug. 19, 2016 (HealthDay News) -- Federal health officials are urging pregnant women to avoid travel to Miami Beach, after Florida Gov. Rick Scott confirmed on Friday that five cases of locally transmitted Zika virus have occurred there.

Until now, local transmission of mosquito-borne Zika -- which can cause devastating birth defects in babies -- has been restricted to a neighborhood in north Miami known as Wynwood. The U.S. Centers for Disease Control and Prevention had already advised that pregnant women not travel to the Wynwood area, and on Friday the agency extended that advisory to include the Zika-affected area of Miami Beach.

"We believe we have a new area where local transmission is occurring in Miami Beach," Scott told reporters during a noon news conference.

The five cases include three men and two women, two of whom are local residents and three who were tourists visiting from New York, Texas and Taiwan.

The area involving this latest cluster of cases includes 1.5 square miles between 8th and 28th streets in Miami Beach, said Scott, who added that there are now 36 confirmed cases of local Zika infection statewide.

"Pregnant women should avoid travel to the designated area of Miami Beach, in addition to the designated area of Wynwood, because active local transmission of Zika has been confirmed," CDC director Dr. Tom Frieden said in a media briefing held Friday.

A broader travel advisory for pregnant women could threaten tourism and heighten fears for pregnant women living in the Miami area.

The Zika virus is typically transmitted via mosquitoes and can cause a transient illness. It is most dangerous to pregnant women, due to the virus' link to microcephaly, a devastating birth defect where babies are born with smaller than normal heads and underdeveloped brains.

Officials continue to struggle with controlling mosquitos in the Wynwood area of Miami, Frieden said.

"Although the state of Florida, with CDC's assistance, has mounted and continues to mount an aggressive response, the mosquitos are persistent and we won't know for at least another couple of weeks if these aggressive control measures have worked," Frieden said Friday.

Outside the Wynwood and Miami Beach areas, Florida health officials have investigated at least four other independent instances of mosquito-borne Zika transmission in Miami-Dade County, Frieden said.

"These are individual instances, and do not represent spread throughout the area," Frieden said.

Occasional individual cases of local transmission cropped up during earlier chikungunya and dengue outbreaks in Florida, but in most instances these did not amount to a new outbreak, Frieden explained.

"For every nine or so one-off cases, where there was a single case of transmission that was locally mosquito-borne, there was one cluster," he said. "The vast majority of local transmissions hit a dead end after one or two people in one household. That's what we would anticipate seeing here."

In other recent Zika news, experts have wondered if the virus might sometimes be transmitted through blood transfusions, and a cluster of infections in Brazil seems to support that notion.

Reporting Aug. 17 in the New England Journal of Medicine, doctors believe that a blood donor passed along the typically mosquito-borne virus in late January to two hospitalized patients who needed transfusions.

"These data show evidence for Zika virus transmission by means of [blood] platelet transfusion," reported a team led by Dr. Iara Motta, of the Jose Alencar Gomes da Silva National Cancer Institute in Rio de Janeiro, and Bryan Spencer of the American Red Cross in Dedham, Mass.

Health officials in the United States have already been preparing for the possibility of Zika transmission via blood transfusion. In March, the U.S. Food and Drug Administration approved an experimental test to check blood donations for the Zika virus.

The FDA also recommends that anyone who has traveled recently to an area where the Zika virus is active refrain from donating blood.

Elsewhere, Texas health officials on Monday reported what appears to be the first case of Zika infection traveling across state lines. A resident of that state who visited Miami recently has tested positive for the virus, state health officials said in a statement.

Things are much worse in the U.S. territory of Puerto Rico, where federal health officials have declared a public health emergency because Zika is spreading so rapidly among residents there. The number of Zika cases there now total 10,690, with 1,035 of those being pregnant women.

And on Thursday, Puerto Rican health officials reported that 30 people have been diagnosed with a rare paralyzing condition that can be caused by Zika infection.

The CDC's Frieden said Thursday he expects even more cases of Guillain-Barre syndrome in Puerto Rico because the Zika virus is infecting so much of the population there.

"We think there will be as many as 200 additional cases [of Guillain-Barre], given the overall number of infections there," Frieden told NBC News.

Health experts do stress that the vast majority of the more than 2,260 Zika infections so far reported in the continental United States have been linked to travel abroad -- to countries with Zika outbreaks in Latin America or the Caribbean.

Most of the thousands of Zika infections recorded globally have so far occurred in Latin America and the Caribbean. Brazil, especially, has reported the vast majority of cases of Zika-linked microcephaly.

U.S. officials said they don't expect to see a Zika epidemic in the United States similar to those in Latin America. The reason: better insect control as well as window screens and air conditioning that should help curtail any outbreaks.

In addition to mosquitoes, the Zika virus can be transmitted through sex. These infections in the United States are thought to have occurred because the patients' partners had traveled to countries where Zika is circulating, the CDC said.

The CDC advises pregnant women not to travel to an area where active Zika transmission is ongoing, and to use insect repellent and wear long pants and long-sleeved shirts if they are in those areas. Partners of pregnant women are advised to use a condom to guard against sexual transmission during pregnancy.

More information

The U.S. Centers for Disease Control and Prevention provides more information on mosquito-borne diseases.

This Q & A will tell you what you need to know about Zika.

To see the CDC list of sites where Zika virus is active and may pose a threat to pregnant women, click here.