The US territory of Puerto Rico declared a health emergency Friday over the Zika virus as the number of cases on the Caribbean island rose to 22, including a pregnant woman.

"Our principal objective is to guarantee the security of Puerto Ricans and to give them advice on necessary preventive measures," Governor Alejandro Garcia Padilla said in announcing the action.

The virus has created alarm since being linked in Brazil to a surge in cases of babies born with abnormally small heads to women who became infected with Zika while pregnant.

Emergency measures being taken in Puerto Rico include freezing the price of condoms. Plans also are being drawn up to combat the Aedes aegypti mosquito that carries the virus.

Earlier this week, US officials confirmed the first case of sexually transmitted Zika, adding another dimension to the outbreak.

"This should be treated as a and rigorous precautions should be taken," the island's health secretary, Ana Rius, said.

Puerto Rican health authorities have reported three new cases of Zika, raising the total to 22. They include an unidentified woman who is pregnant.

Last month, Rius recommended that women avoid pregnancy and said that a quarantine had been established for blood donations.