New Findings on Zika in Semen May Change Recommendations on Preventing Sexual Transmission

A recent study sheds light on how long Zika virus can be transmitted through semen following infection, while another study assessed the side effects of Zika infection on infants with post-natal exposure.

A recent study investigating how long Zika virus lives in semen may bring changes to guidance on preventing sexual transmission of the virus, while another research team has found that post-natal Zika infection in infants may lead to brain damage and behavioral problems.

Zika virus transmission primarily occurs through bites from the Aedes species of mosquitoes, the same mosquitoes that transmit dengue and chikungunya viruses. In addition, the virus can spread through sexual transmission, and from a mother to her unborn baby during pregnancy. While many individuals who catch Zika do not experience symptoms, signs of a Zika infection can include fever, rash, headache, and joint and muscle pain, and the virus has been linked to an increase in Guillain-Barré syndrome. Pregnant women can catch Zika from a mosquito bite or from the semen of an infected partner. Since Brazil’s Zika outbreak, which began in 2015, reported associated cases of microcephaly and other birth defects, public health officials have warned pregnant women of congenital Zika syndrome.

To prevent transmission of Zika during sexual intercourse, the Centers for Disease Control and Prevention (CDC) recommended that couples with a male partner who has the virus or traveled to an area with Zika use a condom or avoid having sex for at least 6 months. In a new study published in the New England Journal of Medicine, a CDC-led research team found that virus shedding in semen might occur within a much smaller time window. The researchers studied 184 American men with symptomatic Zika virus infection to examine the duration and frequency of virus shedding in urine and seminal fluid. They collected 2 specimens per month from each subject for 6 months and tested them by real-time reverse-transcriptase-polymerase-chain-reaction (RT-PCR) assay, for a total of 1327 semen samples from 184 men and 1038 urine samples from 183 men, all obtained 14 to 304 days after illness onset.

RNA from the virus (ZIKV RNA) was detected in 22 of the 36 (61%) men whose semen was tested within 30 days of infection. Overall, Zika RNA decreased substantially in semen after the first month following illness onset, and researchers detected the viral RNA in 1 man at 281 days. Longer periods of virus shedding occurred in older men and in those who reported infrequent ejaculation. Zika RNA in urine was rare.

“Among documented cases of male-to-partner sexual transmission, all have occurred within 41 days after illness onset in the source male partner, and most have occurred within 20 days," the authors wrote. "The absence of reported events occurring at later time points suggests that transmission events coincide with the period during which the virus can be cultured and that detection of ZIKV RNA by RT-PCR may overstate the duration and magnitude of the risk of sexual transmission.” The findings may change CDC recommendations on sexual transmission prevention.

While so much research has focused on prenatal Zika exposure and its prevention, another recent study by Emory University researchers has found that Zika exposure in the early months after birth also presents a risk to infants. In the study, published in the journal Science Translational Medicine, researchers hypothesized that Zika virus infection during the first year of life could cause long-lasting adverse neurological effects. They exposed 8 infant rhesus macaques with Zika virus 5 weeks after birth. To evaluate the impact of the Zika infection, the researchers conducted magnetic resonance imaging (MRI) brain scans on the monkeys at 3 and 6 months of age. They observed effects similar to those that occur in congenital infection, including Zika virus invasion of the nervous system, enlargement of lateral ventricles, alterations in the species-typical emotional reactivity to acute stress, and abnormal maturation of the hippocampus and other brain regions.

“The neurological, behavioral and emotional differences remained months after the virus cleared from the blood of the infants,” the study’s lead researcher Ann Chahroudi, MD, PhD, in a recent statement. The team noted that post-natal Zika infections had less severe effects on the brain than congenital infection and did not have an impact on vision similar to congenital Zika syndrome. “This is why our team now recommends more than just routine monitoring for pediatric patients known to be infected with Zika.”