Texas health officials on Tuesday reported a sexually transmitted Zika virus case.
"The patient was infected with the virus after having sexual contact with an ill individual who returned from a country where Zika virus is present,” said a Dallas County Health and Human Services statement.
The finding confirms that the Zika virus can spread through sexual contact, suggested in earlier scientific reports of men infecting women after travel to African and Southeast Asian countries where the virus was endemic. But it's the first case in the U.S. that was spread locally, as opposed to coming from a mosquito in another country.
Zika has infected an estimated 1 million people in Brazil and has spread to 23 countries in South and Central America in the last year. The outbreak is linked (somewhat mysteriously) to an epidemic of microcephaly, an abnormally small head and brain, in thousands of Brazilian infants. These birth defects were declared a public health emergency by the World Health Organization on Monday.
The U.S. Centers for Disease Control and Prevention noted on Tuesday that the agency had only confirmed the Zika infections by genetic testing, not the sexual
transmission. County officials were the ones who reported the sexual transmission
from someone who had traveled from Venezuela to a patient in the United States who had not been overseas.
The Texas health officials also suggested that it’s important for people who recently traveled to Zika regions to use condoms to prevent transmission of the virus. The disease is largely spread through mosquitoes, but the confirmation of sexual transmission adds a new dimension to the outbreak.
“The real question is how long does the virus stay in semen after an infection?” infectious disease expert Nikos Vasilakis of University of Texas Medical Branch in Galveston told BuzzFeed News. “We just don’t know and we need to find out.”
Sexual transmission of Zika is not unprecedented: In 2011, researchers reported a Colorado scientist had infected his wife with Zika after he returned from Senegal recovered from an infection (both the husband and wife were authors on the paper). While the scientist tested positive for a number of tropical diseases, his wife tested positive only for the Zika virus.
Vasilakis also noted that recent evidence suggests the virus stays alive in saliva for some time after an infection, raising the risk of another way to transmit the disease.
Still, mosquitoes are and will remain the biggest threat, Andrew Haddow of the United States Army Medical Research Institute of Infectious Diseases told BuzzFeed News.
“Mosquitoes are a really effective way to spread a disease, especially in places that don’t have screened windows and air conditioning,” Haddow said.
Haddow and other experts recommended that travelers follow U.S. Centers for Disease Control and Prevention recommendations for visiting Zika-infected regions, which call for strong mosquito avoidance and postponed travel for pregnant women.