Brazil has reported 1,761 cases of babies born with unusually small brains, or microcephaly, the World Health Organization (WHO) said on Tuesday, as a mosquito-borne disease linked to the condition spread across Latin America.

Brazilian health authorities said last month there was a link between the mosquito-borne Zika virus and a surge in babies born with microcephaly, which can cause developmental and intellectual difficulties and limit intelligence and muscle coordination for life.

But the WHO said in a statement on microcephaly that the cause of the outbreak in Brazil had yet to be determined.

As of Dec. 5, the statement, said, 19 children had died out of the 1,761 suspected cases distributed across 422 municipalities in Brazil.

On Dec. 7, Brazil's Ministry of Health revised the definition of microcephaly to include babies with a head circumference of less than 32 cm, instead of 33 cm previously.

Babies in that category will be closely monitored, WHO said.

Indigenous circulation of the virus has been detected in the Americas since February 2014, when Chile confirmed the first non-imported transmission of the disease on Easter Island.

The zika virus has also been confirmed this year in Panama, Venezuela, El Salvador, Mexico, Suriname, Colombia, Guatemala and Paraguay. It is transmitted by the Aedes aegypti mosquito, also known to carry the yellow fever, dengue and chikungunya viruses.

"Because the Aedes species mosquitoes that spread Zika virus are found throughout the world, it is likely that outbreaks will spread to new countries," the U.S. Centers for Disease Control (CDC) says on its Zika webpage.

"Zika virus is not currently found in the United States. However, cases of Zika have been reported in returning travelers."

Between three and 12 days after being bitten by a mosquito carrying the virus, three out of four people come down with symptoms including mild fever, rash, conjunctivitis, headaches and joint pain.

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The WHO does not recommend any travel or trade restrictions due to the Zika outbreaks.

Zika is also found in Africa and Southeast Asia. There is no vaccine or medicine to prevent or treat it, and travelers are advised to protect themselves by avoiding mosquito bites.