By Gene Emery
Zika, the mosquito-borne virus that can cause birth defects in unborn babies, can also be spread to a woman through sexual contact. But a new study suggests the risk may be limited to the first few weeks after symptoms appear in her male partner
“We are going to be reevaluating our guidance on sexual transmission of Zika based on this,” lead author Dr. Paul Mead of the U.S. Centers for Disease Control and Prevention said in a telephone interview.
The CDC currently recommends that couples concerned about the virus use a condom every time or that they not have sex for six months, beginning when Zika symptoms first appeared. Pregnant women are told to use condoms or avoid sex throughout their pregnancy.
And while women seeking to have a child are currently told to wait at least two months before trying to get pregnant after traveling in a Zika-prone area, they are advised to wait at least six months if their male partner has been in a region with the Zika virus, known as ZIKV.
The new research “suggests that there is a short period during which ZIKA-infected men might transmit this virus through sexual contact,” writes Dr. Heinz Feldmann of the National Institutes of Health in an editorial in the New England Journal of Medicine, where the study appears.
“They were not able to find infectious virus at all in the semen after the first month. I think that’s very reassuring,” said Dr. Andrea Ciaranello, director of the Perinatal Infectious Disease Program at Massachusetts General Hospital in Boston, who was not involved in the study.
The researchers tested 184 Zika-infected men who gave semen and urine samples for up to 10 months after their illness
Bits of the RNA that make up the virus were seen in 61 percent of the semen samples taken within 30 days of the illness, then the percentage dropped off rapidly over the next two months, although in one man Zika RNA was seen in semen 281 days after he fell ill.
“But the presence of RNA in the semen doesn’t mean the person can transmit the virus,” said Mead, who is a medical officer in CDC’s Division of Vector-Borne Diseases.
The current recommendations are based on such RNA particles, and “probably what they were seeing before were pieces of dead virus that were lingering, but did not pose any risk,” Ciaranello said in a telephone interview.
In contrast, virus particles grown in the lab and potentially capable of causing an infection were found in only 3 of 78 semen samples, or about 4 percent. No sample older than 30 days showed evidence of being infectious.
“If we look at the epidemiology data,” Mead said, “we find that all documented cases of male to partner transmission have occurred within the first month of illness onset. That would seem to coordinate better with when we can find infectious virus” in the semen than when bits of RNA are present.
Since its discovery in Uganda, Zika has spread to more than 48 countries, producing babies with abnormally-small heads and other birth defects. Cases where the disease was probably acquired through unprotected sex have been reported in at least 13 countries.
While 61 percent of the men in the Mead study had RNA from the virus in their semen within 30 days, the rate dropped to 7 percent after 90 days.
Researchers found that the biggest determinant of how long traces of the virus stayed in the semen was how often the men ejaculated
“After controlling for age, we found that men who ejaculated four times per week during the study cleared ZIKV RNA 21 days earlier than did men who ejaculated once per week,” the study team writes.
They also found that men who had undergone a vasectomy tended to have less virus RNA in their semen than men who had not, and that the virus lingered 12 days longer in men age 50 than in men age 30.
Other factors associated with how long the virus was detectable included the finding that Zika sufferers who had conjunctivitis – better known as pink eye – as part of their illness also tended to have virus-related RNA in their semen 12 days longer.
And, among men who had no joint pain during the illness, Zika RNA was typically detected 27 days longer than in men who did.
In all the reported cases of Zika spread through sex, all have occurred within 41 days and most have been within 20 days, the Mead team notes.
SOURCE: The New England Journal of Medicine, online April 11, 2018
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