Zika virus may persist in semen for months, scientists say
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There’s more evidence that Zika may be transmissible through sex — and maybe for quite a while after infection.

British researchers have reported the case of a man whose semen tested positive for Zika virus 62 days after the onset of his illness. It is the second report of the virus being found in semen. In addition, there have been two cases where sexual transmission of Zika virus is thought to have occurred.

The Centers for Disease Control and Prevention have warned that men who return from places where Zika virus is spreading should use condoms or abstain from sex with pregnant partners. But it is thought that sexual transmission is rare. In general Zika is a virus that people acquire through the bite of an infected mosquito.

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The British scientists reported finding traces of Zika in the man’s semen sample but said they did not grow live virus from it. The difference is important: Seeing traces of virus does not indicate whether the semen could have infected a sexual partner. Live virus, on the other hand, would have been stronger evidence that the man might have been able to infect a sex partner even that long into his recovery.

The report, in the journal Emerging Infectious Diseases, was written by scientists from Public Health England, that country’s equivalent of the CDC. It is posted on the journal’s ahead-of-print page; it will be printed in the May issue.

This case may have informed the agency’s advice on avoiding sexual transmission of Zika virus. Last month Public Health England said that male travelers returning from places where Zika is spreading should use condoms during sex if their female partner was pregnant or might become pregnant.

Alex Hogan/STAT Are you at risk for contracting Zika virus? Your level of risk depends in part on your living conditions.

It advised condom use for men for six months if they had laboratory-confirmed Zika or symptoms compatible with Zika infection. Returning men with no symptoms should use condoms for 28 days, the agency said.

This case involves a man, 68 years old at the time, who returned to Britain from the Cook Islands in the South Pacific in 2014. A week after his return he had symptoms of Zika and tested positive for the virus.

Blood, urine, and semen samples were requested at intervals after he recovered; only the semen tested positive for Zika virus at 27 and 62 days. The letter to the journal does not state if later tests were conducted, so it is not clear whether 62 days represents the end of testing or the point after which no positive tests were recorded.

There are two suspected cases of sexual transmission of Zika virus. An American researcher reported having infected his wife after he contracted the virus in Senegal in 2008; his wife had remained in the United States. Earlier this month Dallas public health authorities reported an infection in a person who had not left the country but had had sex with a person who returned sick from a Zika-affected country.

An earlier report from French Polynesia, published last year in Emerging Infectious Diseases, revealed that traces of virus were found in the semen of a man infected there during an outbreak in 2013.

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