The mosquito-borne Zika virus can be transmitted through sex between gay men, reported the US health authorities.
The case involved a man who traveled to Venezuela and infected his male partner -- who had not traveled -- upon his return to Texas in January.
The couple had been monogamous for more than 10 years, the US Centers for Disease Control and Prevention said.
At least five other cases of sexual transmission of Zika have been described in scientific literature, but those have involved males infecting females.
"Sexual transmission through both vaginal and anal sex is an emerging mode of Zika virus infection that might contribute to more illness than was anticipated when the outbreak was first recognized," said the CDC in its Morbidity and Mortality Weekly Report.
Earlier this week, the CDC said there is no longer any doubt that Zika can cause birth defects, making it the first known mosquito-borne virus with the ability to cause such harm to a developing fetus.