While the main cause of Zika virus transmission is through mosquito bites, scientists have found a case in France, which seemed to indicate that a man traveling back from Rio de Janeiro had passed the virus to his girlfriend through oral sex.

The op-ed, published in the New England Journal of Medicine indicated that after the man presented a rash and muscle pain and it was gone, the same symptoms began appearing in his girlfriend a few days later. The couple tested positive for Zika virus but it was only found in the woman’s urine and saliva, but not in her vaginal fluid or blood, and it was different for the man. The virus was only found in his semen and urine, but not in his blood or his saliva. The woman had said that the only time she’d had contact with her boyfriend’s semen was during oral sex, which might explain this particular case.

Earlier this year, first case of Zika virus transmitted through sexual intercourse has been confirmed in the state of California. The California Department of Public Health (CDPH) revealed the alarming news earlier this month, announcing that a San Diego-based woman, who's neither pregnant nor traveled outside of the country, has been infected.

According to officials, the incident was detected in February after the woman had sexual intercourse with a Zika-infected man who had just returned from a trip to Colombia.

“This is the first confirmed case in California where Zika virus was transmitted sexually,” CDPH Director and State Public Health Officer Karen Smith said in a statement released ending March. “If your partner has traveled to an area where Zika is present, protecting yourself by abstaining from sex or using condoms during sex is the best way to prevent sexual transmission of the Zika virus.”