A study published today in the New England Journal of Medicine sheds more light on how long the Zika virus lives in semen and may change the current recommendations for precautions against sexual transmission of the flavivirus.
While it's been known that semen can transmit the virus, researchers have yet to determine how long semen remains infectious, but the study, by Centers for Disease Control and Prevention (CDC) researchers, shows that the window of time might be shorter than previously thought, usually within 1 month of the initial infection.
Study involved 184 men
To conduct the study, semen from 184 American men with confirmed, symptomatic Zika virus were subjected to two tests: one that detected infectious virus particles, and another that looked for the genetic material of Zika, which can be found even after the virus can no longer cause infection. Researchers sampled urine and semen at 2-week intervals between 14 days and almost 1 year (304 days) after infection during the prospective study.
"We found that shedding of Zika genetic material decreased substantially during the first 3 months after illness but could be detected for as long as 9 months in some men. In contrast, detection of infectious Zika virus particles was rare and limited to a few samples collected within 1 month after illness," Paul Mead, MD, medical officer with the CDC's Division of Vector-Borne Diseases, told CIDRAP News. Mead is the lead author of the study.
Of the 36 men whose semen was tested within 30 days of infection, 22 (61%) had Zika RNA in their specimen. Though Zika RNA detection decreased substantially after 1 month and was mostly undetectable by 3 months post-infection, one man had Zika viral RNA in semen at day 281. Older men, and men who reported ejaculating infrequently had longer periods of virus shedding than younger men.
The researchers detected infectious Zika virus particles—as opposed to genetic material—much less commonly in semen: Infectious Zika virus was found in 3 of 78 semen samples, all within 30 days of illness onset.
Data could change CDC recommendations
"CDC is re-evaluating its guidance for prevention of sexual transmission based on this new information; however, for now, the current recommendations remain in place," Mead said.
Sex, Mead said, is not considered one of the main modes of virus transmission for Zika, which is spread principally by mosquitoes. But the threat of a sexually transmitted infection, especially during pregnancy, is still real.
The current CDC recommendations suggest that any male-female couple practice abstinence or use barrier methods for at least 6 months after the male partner returns from an area with active Zika transmission, even if the male partner is asymptomatic.
"CDC and other public health partners continue to study Zika virus and how it is spread and will share new information as it becomes available." Mead said.
In an accompanying commentary, Heinz Feldmann, MD, from the National Institutes of Health, said the study highlights the limits of molecular testing when estimating a disease's infectivity. Viral isolation, more laborious and time-consuming, is the only way to definitely predict how likely a disease is to be transmitted, Feldmann said.
For public health recommendations, "the goal should be the determination of infectivity, which is probably best assessed by means of viral isolation, which is considered to be less sensitive than molecular detection. Thus, the diagnostic situation is far more complicated than it seems."
See also
Apr 11 N Engl J Med study
Apr 11 N Engl J Med commentary
