Second case of sexual transmission raises new Zika concerns


A case of sexual transmission on U.S. soil of the tropical, mosquito-borne Zika virus, has stirred unease among ordinary people and experts alike.

The lone case, reported Tuesday, highlights how little we know about the virus circulating in Latin America and the Caribbean, where it is suspected of causing a surge in brain-damaged babies.

The infection of a Texan by a partner back from Venezuela is only the second reported case of sexual transmission since the Zika virus was discovered in 1947 and has raised many new questions about the infection, which is harmless to most people and often asymptomatic.

How long does the virus live in sperm? Can people without any symptoms pass it on? What is the level of risk from sex? Nobody quite knows.

Ed Wright, a senior lecturer in medical microbiology at the University of Westminster, said: “In 2008, an American scientist on a field trip to Senegal became infected with Zika virus and is thought to have transmitted it to his wife through sexual contact on his return home. Zika virus has also been found in semen from an individual who was infected during the 2013 outbreak in French Polynesia.

“Given the information we have, potentially over a million cases of Zika caused by mosquito transmission (in the current outbreak) versus two cases of sexual transmission, the additional risk appears small.”

Luis Cuevas of the Liverpool School of Tropical Medicine said, “There is no systematic information on the duration of excretion of the virus in sexual secretions and studies are needed to document whether it remains infectious beyond a few weeks. It is thus advisable adults exposed to Zika follow the recommendation of using condoms until more information becomes available.”