CDC Releases New Zika Virus Guidance as New Sexual Transmission Information Emerges

The Centers for Disease Control and Prevention (CDC) has updated its interim guidance for “pre-pregnancy counseling” for Zika virus, just as new information regarding sexual transmission of the infection has been made available.

Among other provisions, the revised CDC guidance suggests that men with possible Zika exposure but no virus symptoms wait at least 6 months after their last possible exposure before “attempting pregnancy with their partner.” It is also recommended that these men use condoms during this time to prevent sexual transmission of the virus. In a statement released with the guidance update, the CDC said it based its new recommendations on its “ongoing assessment of available data.”

Some of that data likely appears in a series of studies published in the October issue of The Lancet Infectious Diseases, much of which is devoted to Zika virus-related research. In fact, a model for reducing the risk for an outbreak of sexually transmitted Zika virus proposed by researchers from the London School of Hygiene and Tropical Medicine, essentially supports the CDC’s 6-month “window,” noting that earlier studies have found the presence of viral RNA in the semen of infected males for up to 93 days after symptom onset.

Another paper published in the same issue of The Lancet Infectious Diseases suggests that Zika virus RNA may be present in semen and spermatozoa even longer than previously thought. In a case of travel-related Zika monitored by physicians in France, viral RNA was present in multiple collected semen samples 141 days after initial exposure. In two earlier cases investigated by the authors, viral RNA was still detectable in semen 69 days and 115 days, respectively, after symptom onset; in three other cases, however, viral RNA was undetectable after 20 days.

“The viral persistence in semen is of major concern and could be related to a viral tropism for male sexual cells,” the authors write.

In a commentary published in the same issue, authors from the CDC suggest that future assessments of sexual transmission of Zika virus should take lessons from the Ebola outbreak of 2014. They write, “Is the virus associated with spermatozoids or present in the seminal plasma? Is the virus harbored in the testes, a well-known immune-privileged site, or in the prostate? If the virus replicates and persists in the seminiferous tubules, what is the impact on semen quality (eg, morphology, count, mobility)? Answers to these questions could improve diagnostic testing for Ebola virus in semen, elucidate risk factors for viral persistence, and lead to better understanding of possible reproductive sequela of infection. Unfortunately, at the end of the west Africa Ebola virus disease outbreak, these questions remain largely unanswered. These questions are also unanswered for Zika virus.” They go on to suggest that studies designed to address these issues with Zika virus should be conducted “urgently and concurrently” with other disease response activities.

Researchers at the Hospital Universitario La Paz in Madrid, meanwhile, described a case involving “probable” sexual transmission of Zika virus from a 53-year-old male to his 51-year-old wife. The couple had traveled to the Maldives, where the male sustained a mosquito bite, which resulted in infection. Some 18 days after their return home, his wife developed Zika symptoms. Of note, the male had undergone a vasectomy in 2007.

“Although the woman might have acquired Zika virus by mosquito bite, the incubation period if this is the case would be exceptionally long, so sexual transmission from her partner is definitely a possibility,” they write. “Sexual transmission of Zika virus infection from a vasectomized man has not previously been reported.”

As new information continues to emerge regarding sexual transmission of Zika virus and the disease’s effect on pregnant women and their babies, the CDC has focused renewed attention on prevention in pregnant women and women who plan to become pregnant. Of the more than 25,000 Zika cases in the United States and its territories, 2,300 have involved pregnant women, and 22 babies have been born with microcephaly, a birth defect associated with the virus, and have tested positive for Zika, the CDC reports.

CDC director Thomas R. Frieden, MD, MPH, said recently that the agency’s partnership with Colombia’s Instituto Nacional de Salud on a study designed to assess the effects of Zika on babies born to pregnant women infected with the virus should shed new light on how birth defects such as microcephaly develop and, ultimately, how they can be prevented. The study has, to date, enrolled more than 1,000 pregnant women.

“There’s a lot we still don’t know about the long-term problems caused by Zika congenital syndrome,” Dr. Frieden said on a recent conference call with reporters. The study, he added, will be supported with some of the $1.1 billion in Zika funds recently approved by Congress.

Brian P. Dunleavy is a medical writer and editor based in New York. His work has appeared in numerous healthcare-related publications. He is the former editor of Infectious Disease Special Edition.