SEOUL -- The fourth case of a Zika virus in South Korea has been detected from a woman who recently came back from a trip to Vietnam, the Korea Centers for Disease Control and Prevention (KCDC) said Saturday.

The 25-year-old woman worked in Ho Chi Minh City from April 10 to April 30 and entered South Korea on May 1, said the KCDC.

She visited a hospital in the western port city of Incheon on May 4 to treat a chronic thyroid gland problem after having rash and joint pain and was diagnosed with the mosquito-borne virus.

The KCDC suspected that she might have been bitten by a mosquito while in the Southeast Asian nation, noting that the patient is currently in stable condition.

Health authorities are also examining a person who met with the woman in Vietnam between April 13 to April 17 for potential transmission of the virus.

The latest case raises the number of confirmed infections in South Korea to four.

The first South Korean Zika case was found from a 43-year-old man on March 22. The other two Zika cases were confirmed on April 27 and April 29 respectively, from two brothers who had travelled to the Philippines together.

Zika is a virus that is primarily spread by mosquito bites, particularly risky for pregnant women as it is thought to be linked to a rare birth defect- microcephaly that causes newborn babies to have unusually small heads and damaged brains.

The Zika virus is believed not to be spread by ordinary touches between humans, but it can be transmitted through sex and blood transfusion. Cases of sexual transmission from travelers to their sexual partners had been reported from the United States and Europe.

The KCDC advised pregnant women not to travel to Zika-infected countries, while recommending fertile women delay pregnancy for at least two months after returning from those countries.

Zika was first found in Africa and spread to Asia and Lain America. The virus is spreading rapidly in Latin America, while Thailand and the Philippines are the most Zika-infected countries in Asia.