The already troubling spread of the Zika virus got a bit more menacing on Tuesday when health officials in Texas confirmed the first known transmission of the virus through sexual contact. Previously, the only known way the virus could be spread was through mosquito bites. Dallas County health officials said the infected patient had not been to an infected area, but the patient’s partner recently returned from Venezuela.
Concern over the virus has risen steadily across the Americas, where the latest spike in cases has taken place. The World Health Organization declared the outbreak an international public health emergency on Monday, warning as many as 4 million people could contract the virus. The symptoms of Zika can be pretty mild—fever, fatigue, headache, you know the drill—fatalities are rare, and most people who get infected (up to 80 percent) don’t have any symptoms at all. The virus, however, has been linked to birth defects in babies born to infected women, which has set off an alarm across Latin America.
There are still many, many unknowns about the virus and its link to birth defects in newborns. Worries over microcephaly, a condition where babies have underdeveloped brains and abnormally small heads at birth, however, have caused several countries to discourage women from getting pregnant until more is known about Zika’s impact on pregnant women. Brazil has been the hardest hit so far by microcephaly; it is investigating 3,670 suspected cases, according to the BBC. The cases of Zika have extended almost throughout the entirety of South and Central America, and as far away as Australia.