A mosquito control truck passes through a neighborhood in Hillsborough County, Fla., Tuesday night, spraying insecticide. (Scott Audette/ Reuters)

Florida officials have declared a public health emergency in four counties with confirmed  Zika virus cases, underscoring the increasing concern in the United States. Meanwhile, U.S. health officials have added two more countries to the travel advisory for pregnant women.

Florida Gov. Rick Scott delivers his state of the state address during a joint session, Tuesday, Jan. 12, 2016, in Tallahassee, Fla. (AP Photo/Steve Cannon) Florida Gov. Rick Scott. (AP)

Gov. Rick Scott (R) said nine cases had been confirmed in Miami-Dade, Hillsborough, Lee and Santa Rosa counties and all appear to be "travel-associated." That means that officials believe the patients likely contracted the virus outside the state and most likely outside the country in one of the regions where the virus is spreading.

"We know that we must be prepared for the worst even as we hope for the best," Scott said in a statement.

Everything you ever wanted to know about the Zika virus and its spread across North and South America. (Daron Taylor,Claritza Jimenez/The Washington Post)

The Centers for Disease Control and Prevention has been reassuring Americans for days now that none of the cases seen so far have been due to mosquitoes that have made their way to the United States and that therefore Zika is not a major threat to public, yet. Scott appeared to acknowledge this in his executive order, but he also said that he was taking this action to "ensure Florida is prepared and stays ahead of the spread of Zika virus in our state."

Scott's directive gives the Health Department additional power in coordinating a response to Zika and directs the state's environmental unit to cooperate with the Agricultural Department in coming with additional mosquito control measures.

Florida already has one of the strongest mosquito control programs in the country, but has grappled with small outbreaks of two other mosquito-borne viruses—dengue and chikungunya--that worked their way up from Central America. Residents infected with those pathogens had not traveled outside the United States.

Tom Frieden, director of the Centers for Disease Control and Prevention, said aggressive mosquito control is key to stopping the spread of Zika as well as other mosquito-borne illnesses.

“How they decide to do that is up to the state,” he said.

Also Wednesday, the CDC added two more countries, Jamaica and Tonga, to its list of countries that pregnant women should avoid. The full list, which can be found here, now includes the lower half of the Americas.

The CDC recommends that women who are pregnant or trying to be take the following precautions:

  •  Pregnant women should consider postponing travel to the areas where Zika virus transmission is ongoing. Pregnant women who must travel to one of these areas should talk to their doctor or other healthcare professional first and strictly follow steps to avoid mosquito bites during the trip. Until we know more, if your male sexual partner has traveled to or lives in an area with active Zika virus transmission, you should abstain from sex or use condoms the right way every time you have vaginal, anal, and oral sex for the duration of the pregnancy.
  • Women trying to become pregnant should consult with their healthcare professional before traveling to these areas and strictly follow steps to prevent mosquito bites during the trip.

This post has been updated.

Read more:

Dallas reports case of Zika spread through sex; CDC urges condom use

Zika and sex: Seven key things you need to know about the case in Dallas

FAQ: What is Zika, and what are the risks as it spreads?

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