New cases of the Zika virus, which is linked to birth defects, have been confirmed in the U.K., health officials said.

Three British travelers have been diagnosed with the mosquito-borne disease after visits to Colombia, Suriname and Guyana, according to Public Health England. The government agency did not provide further details about the cases but said the Zika virus “does not occur naturally in the U.K.”

The virus is typically found abroad and has become a growing threat in the U.S., where cases have been confirmed in Florida and Illinois. It’s also spreading in South America, Central America and the Caribbean.

Read More: 5 Things to Know About the Zika Virus

The U.S. Centers for Disease Control and Prevention has warned pregnant women to reconsider traveling to the areas where they would be at risk of contracting the virus, as federal health officials push to develop a vaccine for it.

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