(CNN) Three British travelers have been infected with the Zika virus, health officials revealed this week.

"As of January 2016, three cases associated with travel to Colombia, Suriname and Guyana have been diagnosed in UK travelers," Public Health England said on its website

The government agency did not provide further details about the cases but added that the virus "does not occur naturally in the UK."

Zika "is not spread directly from person to person," it said.

Travel warnings

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The announcement came on the heels of last week's travel alert from the U.S. Centers for Disease Control and Prevention (CDC) recommending pregnant women postpone travel to Brazil, Colombia, El Salvador, French Guiana, Guatemala, Haiti, Honduras, Martinique, Mexico, Panama, Paraguay, Suriname, Venezuela and Puerto Rico.

On Friday, the CDC expanded its travel warning to include Barbados, Bolivia, Ecuador, Guadeloupe, Saint Martin, Guyana, Cape Verde and Samoa.

The recommendations also call for women who have traveled to these places during their pregnancy be screened and monitored for the virus if their visit took place while the virus was present in the country they visited.

Pregnancy risks

Zika virus is a mosquito borne disease. An individual becomes infected by the bite of an infected mosquito. Symptoms of the virus include fever, rash, joint pain and red eyes and can last from a few days to about a week. But 80% of individuals infected have no symptoms.

The virus has been linked to an increase in cases of a rare neurological condition called microcephaly in babies. Microcephaly results in babies being born with abnormally small heads, and often serious, and sometimes deadly, developmental delays.

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It prompted the Salvadoran vice minister of health to tell women there not to get pregnant for two years, echoing similar warnings in Colombia and Jamaica.

"We're recommending that women who may get pregnant plan their pregnancies and try to avoid getting pregnant this year and the next," Eduardo Espinoza told CNNEspanol Thursday.

Women's rights groups have called on the government to lift El Salvador's total abortion ban in light of the news.

"I think the Zika situation puts the total abortion ban into the national arena," said Astrid Valencia of Amnesty International.

Since 1998, El Salvador has banned all abortion, even in cases of rape, incest, fetal deformation or where the mother's life is at stake.

A worker fumigates against Zika virus carrying mosquitoes in Peru.

No treatment

There is no prevention or treatment. Travelers to dangerous areas are urged to prevent mosquito bites by using mosquito repellant and covering exposed skin.

The aedis aegyptia mosquito, which transmits the disease, bites all day long, so individuals need to reapply that repellant and not let their guard down. Aedes albopictus mosquitoes, which are found throughout the U.S. and are known for transmitting dengue fever and chikungunya, may also transmit the virus, the CDC said Friday.

However, mosquito bites and mother to unborn baby aren't the only ways this virus is transmitted. The new CDC report notes documented cases of infection from sexual transmission, blood transfusion and laboratory exposure.

Stephen Higgs, president of the American Society of Tropical Medicine and Hygiene, told CNN that once a person is infected with the virus, it is likely that they will develop an immunity to future infection.