Zika virus RNA was detected in the blood of five pregnant women who had been exposed to the virus at least 2 weeks prior to PCR testing, case reports from the CDC's U.S. Zika Pregnancy Registry showed.

This adds to the evidence that Zika virus may be detectable in pregnant women for longer than previously thought, reported Dana Meaney-Delman, MD, of the CDC, and colleagues.

The CDC recently updated their guidance to providers treating pregnant women to expand the window where real-time PCR testing can be used -- from 7 days to up to 14 days following exposure, and these results seem to support these new recommendations.

Writing in a special fast-tracked study in Obstetrics and Gynecology, the authors examined five pregnant women who had traveled to or lived in countries with active Zika virus transmission -- four of whom were symptomatic, while one was asymptomatic. Zika virus RNA was detected via real-time RT-PCR in the serum of the four symptomatic pregnant women from a range of 17 to 46 days following exposure, and in the asymptomatic woman 53 days after exposure.



One symptomatic woman had evidence of Zika infection in the fetal tissue, and opted for pregnancy termination. Similar to prior fetal autopsies, Zika virus RNA was discovered in the skeletal, muscle, bone, and placenta, but not the umbilical cord, liver or lung tissue.

Two symptomatic and one asymptomatic woman went on to deliver healthy infants, while one symptomatic woman has an ongoing pregnancy. However, new research indicates that it is possible that the effects of congenital Zika virus infection may not manifest until later in a child's life.

With these new cases, there have now been a total of eight pregnant women with evidence of Zika virus detected in their blood for a prolonged exposure. These data seem to confirm animal studies that have discovered similar results when comparing pregnant subjects compared to non-pregnant subjects. Meaney-Delman and colleagues noted that other infectious diseases associated with adverse pregnancy outcomes, such as hepatitis E, follow similar patterns.

"Delayed immune clearance of viruses from the maternal circulation may reflect altered immunity during pregnancy," they wrote. "Alternately, fetal infection and ongoing viral replication in the fetus or placenta might result in the transfer of viral genetic material into the maternal circulation."

Further research is needed in a larger population of women to determine whether or not pregnancy status impacts how long Zika virus RNA stays in a patient's blood. If confirmed, the CDC has the potential to expand their real-time RT-PCR assay, the Tripolex test -- which detects Zika virus RNA in serum and cerebrospinal fluid, and can be used for urine and amniotic fluid, as well. This test also rules out similar flaviviruses, dengue and chikungunya.

"Expanding real-time RT-PCR testing may provide additional diagnostic information and increase the proportion of pregnant women with Zika virus infection who receive a definitive diagnosis," the authors conclude. "[This] may improve our understanding of the diagnostic, epidemiologic and clinical implications of prolonged detection of Zika virus RNA during pregnancy."