U.S. health authorities are urging men to wait six months before trying to conceive a baby with their partner if they have traveled to an area with the Zika virus, which can cause devastating birth defects. The U.S. Centers for Disease Control and Prevention on Friday extended the time recommendation for men from eight weeks to six months, after researchers found the virus can linger in semen for months. The agency recommended men use condoms or refrain from sex for at least six months after returning from a Zika-hit area, even if they show no symptoms of the virus. Zika causes only mild symptoms in adults, including fever, rash and red eyes — and some people experience no symptoms. However, pregnant women who are infected with the virus risk giving birth to babies with microcephaly, a birth defect that leads to abnormally small heads. Earlier Friday, officials in Thailand confirmed two cases of babies with microcephaly that were caused by the Zika virus, the first confirmed causes of the condition linked to the virus in Southeast Asia. The World Health Organization urged countries in the region to take stronger measures to combat the virus. Mosquitoes are already a big concern in Thailand because they also transmit malaria and dengue fever. While the Zika virus has been present in Southeast Asia for years, health officials say there has been an increase in the number of cases in recent months. On Thursday, U.S. health officials recommended that pregnant women postpone non-essential travel to 11 Southeast Asian countries, including Thailand, because of the ZIka risk.