First Sexually Transmitted Zika Virus Case Reported in Oregon

Oregon officials say the man had traveled to an area affected by the mosquito-borne virus, and then infected a woman after his return.

Officials say the virus, which is similar to West Nile or Yellow Fever, has previously only been known to be transmitted by mosquitoes.

Only about 1 in 5 people who are bitten or infected will actually show signs, including fever, rash, joint pain and conjunctivitis (watery, itchy eyes). The virus was first discovered near Uganda in 1947, but until recent years has largely been confined to the African continent.

The biggest concern is for pregnant women, and there is evidence to suggest those who are infected while being pregnant can experience some birth defects to their unborn child.

These include microcephaly, or the baby's head being too small.   Oregon officials say those who have traveled outside the U.S. to a potentially affected area should refrain from sexual activity for at least a month, or utilize condoms.

Generally, once someone has returned from an area known to be affected by the virus, if they show no signs within 3-4 weeks they are considered to not be infected.  People who do get the virus develop an immunity and usually don't get it again even if they are infected a second time.