Florida Gov. Rick Scott has declared a health emergency in four counties of the state because of the Zika virus.

At least nine cases of the mosquito-borne illness have been detected in Florida. Health officials believe all of the cases are from people who contracted the disease while traveling to affected countries.

Scott signed the order Wednesday to cover Miami-Dade, Lee, Hillsborough and Santa Rosa counties.

The Zika virus is linked to brain deformities in babies and is causing concern among public health officials worldwide. The virus is primarily spread through mosquito bites, but investigators had been exploring the possibility it could be sexually transmitted.

U.S. health officials say a person in Texas became infected with Zika through sex in the first case of the illness being transmitted within the United States.