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Study Suggests Existing RT-PCR Assays Can Detect Ebola Virus in Semen

NEW YORK (GenomeWeb) – A study by investigators from the National Institute of Allergy and Infectious Diseases suggests that existing RT-PCR assays can pick up the presence of Ebola virus in semen samples from survivors who are otherwise deemed disease-free.

In the Journal of Infectious Diseases this week the researchers reported how they spiked half a dozen semen samples and half a dozen whole-blood samples with serial dilutions of EBOV. They then looked at whether the virus could be detected using RT-PCR-based assays that are already being using with Emergency Use Authorization for finding EBOV in whole-blood or plasma samples.

Indeed, the team found EBOV RNA in the semen samples using the TaqMan EZ-1 real-time RT-PCR assay — originally designed to detect the Ebola Zaire virus — and the Minor Groove Binding (MGB) quantitative RT-PCR assay, suggesting such tests may be useful for identifying individuals who may be at risk of unwittingly passing on the virus.

"The assumption that performance of these assays is the same for spiked versus authentic samples is reasonable but should be monitored in the field," corresponding author Peter Jahrling, who is with NIAID's integrated research facility division of clinical research, and his colleagues wrote.

"This study now opens the door to test semen from EBOV survivors for the presence of residual viral RNA," they explained, "as well as to facilitate epidemiological investigations to rapidly identify sources of new cases as well as potential at-risk contacts."

It has been known for some time that EBOV can make its way into semen and other body fluids in individuals with existing or recent EBOV infections, the researchers noted.

But sexual transmission of the disease was not described until earlier this year, when an individual from an apparently Ebola-free region in Liberia contracted the virus after having intercourse with someone who survived EBOV infection and had been released from the hospital more than five months earlier.

"[T]he potential for sexual transmission of Ebola in West Africa has become a critical concern," they wrote, "and the urgent need to screen survivors for the presence of EBOV RNA in semen has been realized."

Because existing PCR-based assays have only been approved for use in whole blood or plasma, though, the team set out to test their feasibility for Ebola detection in seminal fluid.

To do this, the researchers spiked serial dilutions of live EBOV into six semen and six blood samples. After extracting viral RNA with a Qiagen QIAamp kit, they tested the samples using reagents and protocols associated with the EZ-1 and MGB RT-PCR assays, which are used at Liberia's National Reference Laboratory and other sites in West Africa.

The team did not see significant differences in EBOV RNA detection when comparing the blood and semen samples.

The researchers saw hints that the MGB-1 assay may have slightly higher sensitivity for finding the so-called Makona version of EBOV compared with the EZ-1 assay, though they noted that more research is required to determine whether that difference is significant.

It also remains to be seen how well such assays pan out when applied to other sample types such as urine or saliva, the authors noted. In the meantime, they argued that the EZ-1 assay's performance in semen samples appears to be on par with that in blood, offering promise for real-world testing on these samples.