Richard Leman on Zika.jpg

Dr. Richard Leman, public health physician, says an Oregon woman was infected by the Zika virus while traveling abroad.

(Lynne Terry/Staff)

The Oregon Health Authority has identified the first sexually-transmitted case of Zika in Oregon, officials said Friday.

A woman was infected with the virus through her partner who had traveled to a Zika-affected country and developed symptoms shortly after he returned, according to a news release. The woman had not traveled, but she and her partner both tested positive for Zika after having unprotected sex.

During a Friday news conference Dr. Richard Leman, public health physician, declined to say where the woman lives for confidentiality reasons. He said officials learned of the case during the past week, but it took them some time to confirm it.

>>> Watch the Friday press conference with Dr. Richard Leman, public health physician

Oregon has recorded a total of five Zika cases in 2016, and the risk of contracting the virus in the state remains low, Leman said. Previously, the state had tracked three other cases - one in 2014 and two in 2015.

Health officials said Friday that sexual transmission of the virus could be more common than they initially believed. In addition to the Oregon case, the Centers for Disease Control and Prevention is investigating 13 other possible cases of sexually-transmitted Zika infections across the country, Leman said.

The virus is mainly carried by one species of mosquito, Aedes aegypti, that thrives in tropical and subtropical climates. It also can be carried by another species, Aedes albopictus, which can survive in cooler temperatures. Neither exists in Oregon. But there are Aedes aegypti in parts of the South and Hawaii. Unlike some other mosquitoes, both species bite during the day.

"Though mosquito bites appear to be the most common way Zika is spread, there is increasing evidence for sexual transmission as well," Leman, the public health physician, said in a news release.

It's not known whether asymptomatic men can transmit the virus. Leman said men who are tied to sexually transmitted cases all had exhibited symptoms.

Only about a fifth of those infected with Zika come down with mild symptoms, which include fever, rash, joint pain and conjunctivitis or red eye. But officials fear that the virus is linked to a birth defect in about 5,000 babies in Brazil. They were born with shrunken heads and brains, a condition known as microcephaly. Public health officials say that fetuses may be at the greatest threat during the first trimester.

The CDC recommends that men who've traveled to an affected area abstain from sex with a pregnant woman or use condoms. Health officials have advised women who are pregnant to avoid nonessential travel to Zika-affected areas. If traveling is necessary, pregnant women should cover up when outside, stay in places with screens or air conditioning and use insect repellents.

Leman said women who have traveled to affected areas and wish to become pregnant should wait six weeks after their trip.

Oregon officials have asked health care providers to have patients tested if they've been to an affected area and are pregnant or developed two of the four symptoms.

-- Rebecca Woolington and Lynne Terry

503-294-4049; @rwoolington