The U.S. Centers for Disease Control and Prevention issues a travel advisory on the Zika virus for 11 Southeast Asian countries, including the Philippines.

(Reuters) — U.S. health officials on Thursday recommended that pregnant women postpone travel to 11 Southeast Asian countries because of the risk of Zika virus infection, which has been shown to cause severe birth defects.

The latest countries singled out by the U.S. Centers for Disease Control and Prevention are Brunei, Myanmar, Cambodia, Indonesia, Laos, Malaysia, Maldives, Philippines, Thailand, Timor-Leste (East Timor), and Vietnam.

The CDC said Zika has been present in areas of Southeast Asia for many years, and several countries have reported occasional cases or small outbreaks. The agency said there have been recent variations in the number of cases reported in the area and, although many people who live there are likely immune, U.S. travelers may not be.

While the level of risk is unknown, Zika virus infection during pregnancy causes severe birth defects, including microcephaly and other severe brain abnormalities, the CDC said in a statement.

Zika, which is mainly a mosquito-borne disease, was first detected in Brazil last year and has been spreading globally.