Dallas County health officials on Tuesday confirmed a case of Zika infection through sexual transmission, the first confirmed case of locally acquired Zika in the U.S. during the current outbreak.
Authorities stressed, however, that transmission via mosquito bites still represents the greatest risk for the virus to spread widely in the United States.
According to Dallas County health officials, a person was infected after sexual contact with someone who had recently returned from Venezuela, which has reported more than 4,700 cases of Zika.
"Now that we know Zika virus can be transmitted through sex, this increases our awareness campaign in educating the public about protecting themselves and others," said Zachary Thompson, director of Dallas County Health and Human Services. "Next to abstinence, condoms are the best prevention method against any sexually transmitted infections."
Zika infections are generally mild, and many infected people experience no symptoms. The disease can cause fever, rash, muscle and joint aches and red eyes. It also has been linked to the birth defect microcephaly and to other poor birth outcomes in some women infected during their pregnancy.
Public health agencies have recommended that pregnant women should reconsider travel to affected areas of Latin America. If these women must go, they should take precautions against mosquito bites.
Safety measures
News of the sexually transmitted case in Dallas changes the public health message, said Dr. Kristy Murray, an epidemiologist at Baylor College of Medicine and Texas Children's Hospital."Now I think we can officially say they need to be concerned about potential spouses traveling from those areas as well," Murray said.
An infected traveler, she says, might feel perfectly healthy, yet still have the potential to pass on the virus.
"A lot of this is evolving and we don't know the risk to pregnant women," Murray said. "I think right now it's safe to say they also need to self-defer from sexual activity for a month or if they choose to engage, at least use condoms to prevent transmission."
Officials cautioned that sexual transmission of Zika is still unlikely to be common in the U.S., and that the greater risk will come from mosquitoes that bite infected people and pass the virus on to others.
"To date, of the almost two million cases of Zika globally, most of them in the Western Hemisphere, this case in Dallas is only the third documented instance of sexual transmission," said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine. "Therefore the overwhelming emphasis should remain focusing on Aedes mosquito prevention."
That includes removing standing water that can provide breeding sites around homes and urging travelers to Latin America to use mosquito protection during their travels and for up to four weeks after they return. Blood banks are asking travelers to refrain from donating blood for 28 days after returning.
'Prevent and present'
Little is known about the risk of sexual transmission of Zika virus."We do know that the virus is remaining in the semen, but the question is for how long?" said Dr. Nikos Vasilakis, assistant professor of pathology at the University of Texas Medical Branch at Galveston.
It's also unclear whether transmission only occurs through infected semen or whether infected women may pass the virus on as well. Authorities would not disclose the gender of the person infected in Dallas County.
Murray said it's likely that sexual contact would expose a victim to a larger amount of the virus than a mosquito bite. This could increase the risk of symptoms or shorten the incubation period before symptoms arise.
The best documented case of sexual transmission occurred in 2008. Brian Foy, a scientist with the Centers for Disease Control and Prevention, had been conducting research on mosquitoes and malaria in Senegal, and became ill once he returned to northern Colorado.
Four days later, his wife, Joy Chilson Foy, also became ill despite not having traveled. Blood tests later confirmed that both were infected with Zika. Foy had also reported a swollen prostate and blood in his semen.
During a 2013 Zika outbreak in French Polynesia, researchers documented the case of a Tahitian man who experienced blood in his semen, two weeks after an illness that involved a fever. Tests confirmed the presence of the virus in his semen as well.
Dr. Umair Shah, executive director of the Harris County Health Department, said local officials were monitoring the investigation into the Dallas County case, but for now, the message to residents to "prevent and present" remains unchanged.
"Prevent yourself from getting bit by a mosquito that has the potential to carry Zika virus, and if you develop symptoms, present yourself to your health care providers," he said.
(c)2016 the Houston Chronicle
