In the ZIKV-019 study, a fetus infected with Zika virus died in utero. Subsequent analyses showed that Zika virus RNA was detected in many tissues, far more than we've detected at term in any pregnancy studied to date. A major outstanding question is whether this viral RNA indicates replication-competent virus. There is increasing evidence that not all tissues where viral RNA is detected contain replicating virus. To address this question, we sent tissues to Xiankun (Kevin) Zeng from USAMRIID who has developed an assay to detect negative sense RNA. Briefly, our viral RNA qRT-PCR assay detects positive-sense RNA which can exist in the presence or absence of replicating virus. Negative sense RNA, in contrast, is produced only as a replication intermediate, which means that its detection is evidence of active virus replication.
As shown in this PDF
from Dr. Zeng, negative sense RNA was detected in:
- fetal colon
- fetal amniotic/chorionic membrane
- fetal lung
Here is an example of the negative sense RNA staining:
While we were unable to examine all fetal tissues with this method, this data provides unequivocal support for a systemic, disseminated Zika virus infection in this fetus.
This method will also be extremely valuable for assessing whether the detection of Zika virus RNA in other tissues (e.g., lymph nodes, semen, red blood cells) correlates with the presence of actively replicating virus, which, at the present time, is not established.