Zika Virus Remains in Bodily Fluids Longer Than Other Flaviviruses

Researchers and clinicians alike know that Zika virus remains in the bodily fluids of those infected for a significant amount of time, increasing the risk of transmission via sexual contact and other routes. Now, as mosquito season approaches in parts of North America, there is new understanding of exactly how long the mosquito-borne virus remains in blood, urine, and semen of infected humans.

In a study published February 14th in The New England Journal of Medicine (NEJM), a team from the Centers for Disease Control and Prevention (CDC), Emory University in Atlanta, Caduceus Healthcare in San Juan, Puerto Rico (PR), and Ponce (PR) University School of Medicine—Saint Luke’s Episcopal Hospital Consortium found that Zika is present in serum for a longer duration than other flaviviruses—namely, Dengue.

“It is not well understood how often Zika virus particles can be detected in semen and other body fluids and for how long they remain detectable,” study co-author Gabriela Paz-Bailey, MD, MSc, PhD, CDC Behavioral Surveillance Team Lead told Contagion^®. “Existing evidence is based on case reports and cross-sectional observations, primarily from returning travelers. This study is unique in that 92% of participants were enrolled within 1 week after symptoms of Zika began, providing a clearer understanding of virus detection early in the course of infection. It is also the first study to examine multiple body fluids for the presence of Zika virus in an ongoing fashion.”

For their research, Dr. Paz-Bailey and colleagues analyzed samples from 150 participants (55 of whom were male) with detectable Zika virus RNA (via reverse transcription polymerase chain reaction (RT-PCR)) in urine or blood in an enhanced arboviral clinical surveillance site. They collected serum, urine, saliva, semen, and vaginal secretions weekly for 1 month, and then subsequently at 2, 4, and 6 months, testing them via RT-PCR (anti-Zika virus IgM enzyme-linked immunosorbent assay was used to test serum). For study participants with detectable virus RNA in any specimen at week 4, samples were collected biweekly until all tested negative for Zika. The authors used parametric Weibull regression models to estimate the time detectable Zika RNA remained in each body fluid.

The researchers found that half of the study participants had detectable Zika RNA in serum for 14 days (median) after the start of symptoms and that 5% of the participants still had virus present in serum at 54 days (median) following symptom onset. In collected urine specimens, half the participants had detectable RNA at 8 days (median) following symptom onset, and it was still present in 5% of participants 39 days (median) after they fell ill. Finally, in collected semen, half of the samples were positive for Zika RNA 34 days (median) after symptom onset, and for 81 days (median) for 5% of study participants.

“The study found that Zika virus particles were more likely to be found in serum than in urine,” Dr. Paz-Bailey explained. “However, about 10% of participants only tested positive in urine and not in serum. Therefore, there is some modest benefit in testing both urine and serum in patients with suspected Zika virus infection. Outside this study, there have been only 2 case reports of men whose semen still had detectable Zika for more than 6 months after symptoms began. Based on our findings, such late detection seems unusual. It remains unclear whether those with detectable RNA pose an infection risk to partners at these time points.”

She added that because she and her colleagues have concluded that the risk of spreading the virus to others via sexual contact “is minimal at 6 months,” the CDC “will continue to recommend that men who have been exposed to Zika should use condoms or not have sex for at least 6 months from the start of symptoms or from their last exposure” to the virus.

“[The NEJM] results were part of an interim analysis and several participants still had detectable Zika virus particles at their most recent visit,” she said. “We will continue to follow up with participants until reaching the planned sample size and estimates on how long evidence of Zika stays detectable in the body will be updated once complete information is available.”

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.