Florida health officials said Tuesday they are investigating a potential case of Zika infection that was not contracted by someone traveling to a region affected by the mosquito-borne virus.

Until now, there has been no sign that mosquitoes carrying Zika have arrived in the continental US, but officials have warned that the possibility was looming. The US territory of Puerto Rico has seen a spike in cases in recent months.

It was not immediately clear whether the Florida case involved mosquito bites or , since both are known routes of transmission.

The Florida Health Department "is conducting an investigation into a possible non-travel related case of Zika virus in Miami-Dade County," it said in a statement.

The US Centers for Disease Control and Prevention said Florida had confirmed a Zika infection, and that the CDC is "closely coordinating with Florida officials," according to a statement sent to AFP.

The CDC said federal authorities would, upon request, "conduct additional laboratory testing."

As of mid-July, there have been 1,306 cases of Zika in the continental United States, nearly all involving people who had traveled to areas in Latin America and the Caribbean basin that are affected by the current outbreak.

Fourteen of the cases were transmitted by sexual contact between those who had traveled and their US-based partners.

Earlier this week, a case emerged in Utah in which a caregiver appeared to have been infected by an elderly patient, though the exact route of transmission remains unknown.

Birth defects

Zika is a concern because if a pregnant woman is infected, she faces a higher risk of bearing a child with microcephaly, in which the skull and brain are malformed and smaller than normal.

The "CDC has been working with state, local, and territorial health officials to prepare for the possibility of locally acquired Zika infection in the United States," the agency said.

"To date, CDC has provided Florida more than $2 million in Zika-specific funding and about $27 million in emergency preparedness funding that can be used toward Zika response efforts."

The Florida Department of Health said Zika prevention kits and repellent would be available for pickup at the health department and distributed in the area being studied.

"Zika kits are intended for ," the health department said.

"Mosquito control has already conducted reduction and prevention activities in the area of investigation."

Zika virus can cause a variety of symptoms, including rash and joint and muscle pain, but often carries no symptoms at all.

Zika can also trigger Guillain-Barre Syndrome, which leads the immune system to attack the nerves and may lead to paralysis.

Zika virus was first identified in 1947 but is poorly understood, and there remains no vaccine to prevent it or medicine to treat it.

Officials urge pregnant women to avoid traveling to Zika-affected areas and to wear mosquito repellent to reduce the risk of being bitten.

Condoms or abstinence are also recommended to reduce the risk of infection by people traveling to or living in places where Zika is circulating.