Don’t panic. That’s the emphatic message coming from researchers who have discovered a new virus in human blood. Though it’s unclear how common the pathogen is, there’s no evidence that it has caused anyone harm, and half of those infected appear to have cleared it.
The newfound virus’s genetic sequence shows that it has similarities to hepatitis C, which can cause serious liver damage, and to the harmless—and even helpful—human pegivirus (formerly dubbed hepatitis G). Amit Kapoor, a virologist at Columbia University led the team that identified the new virus—and which has named it human hepegivirus 1, or HHpgV-1—notes that many people understand that humans coexist with myriad bacteria that are not dangerous, but they don’t realize the same holds true for some viruses.
The team made the discovery thanks to new, sophisticated techniques for sequencing fragments of RNA and DNA. As part of a search for novel human viruses, the group scoured blood samples from a cohort of 46 people that were collected before and after they received a blood transfusion between 1974 and 1980. Today, stricter policies determine who can donate blood and the blood itself is screened more rigorously. “I thought if I want to know whatever is circulating and unknown these are the best samples,” Kapoor says.
Using what’s known as “deep sequencing” techniques, Kapoor’s team fished for nucleic acid sequences (the building blocks of DNA) of known viruses, and found two people who posttransfusion had what looked like a novel flavivirus, the family that includes hepatitis C and human pegivirus. Based on later blood samples that were analyzed, both of these people subsequently cleared the virus, the team reports online today in mBio. Kapoor and his colleagues then looked at 70 more people from that cohort but did not find the HHpgV-1 sequence again.
An analysis of a different batch of stored blood samples, from 106 people who had received many blood products because they had hemophilia, found two more people who harbored HHpgV-1 sequences. These people had persistent infections, one of which lasted at least 5.4 years, but no evidence of a related disease.
The researchers have yet to isolate the virus itself or produce it in cell cultures, but viral hunters are convinced it exists. Although contamination frequently upends the supposed discovery of a new virus, HHpgV-1 looks real, says Michael Houghton, a virologist at the University of Alberta in Edmonton who helped identify the viral cause of hepatitis C. Yet Houghton stresses that many unknowns remain. “While this elegant and valuable work serves to emphasize the power of modern deep sequencing technology in identifying new viruses, the role of this new virus in liver and other diseases remains to be elucidated,” he wrote in an email.
Still, it is far too early for blood banks to take any action against HHpgV-1, says Michael Busch, an experimental pathologist who co-directs the Blood Systems Research Institute in San Francisco (an arm of nonprofit blood banks) and former member of a U.S. government advisory group about blood safety. “Does it cause trouble that would justify any response with blood safety? I don’t think we’re at that level.” Many blood products today, such as plasma, go through filtering and inactivation procedures that likely eliminate HHpgV-1, he notes. Moreover, there’s a chance the virus could even be helpful. Busch co-authored studies that show that HIV-infected people benefit from co-infection with hepegivirus, which makes up a portion of HHpgV-1’s genetic sequence. “There was clear evidence that it reduced the pathogenesis of HIV,” he says.
Kapoor says the main challenge now is to develop an antibody test to determine who is or was infected with HHpgV-1 in a larger population. Researchers then can compare the health of people with HHpgV-1 antibodies with control groups and assess whether any links to disease exist.
Almost every year, scientists identify a new virus in humans, Busch says, and some undoubtedly were spread through transfusions. In the same study that found HHpgV-1, Kapoor’s team found 10-fold more anelloviruses, unknown until 1997, in posttransfusion blood samples. Yet no studies have convincingly linked these viruses to disease. “Anelloviruses are probably the most common human virus,” notes virologist Eric Delwart of the University of California, San Francisco, who was a postdoctoral adviser to Kapoor. “They’re very understudied.”
Delwart, who says his lab has already discovered a sequence that looks like one from HHpgV-1 in a stored blood sample, predicts that as researchers find more diverse variants of the virus, they can begin to address the intriguing questions of its origin. “Where are these viruses coming from?” Delwart asks. “Are they recently in the human population or have they been around for a long time?”