New viruses are popping up all over these days – Heartland virus in Missouri last month, a new virus in the same family as SARS in Saudi Arabia this month. And now, a never-before-seen hemorrhagic fever virus in central Africa.

It's called Bas-Congo virus after the province where it was found just west of Kinshasa, the teeming capital of the Democratic Republic of Congo. The discovery was announced today in the journal PLoS Pathogens.

So far only three people in the remote village of Mangala are known to have contracted Bas-Congo hemorrhagic fever, two of whom died. One was a health care worker who cared for the other two villagers, which means it can apparently be transmitted from person to person, although no one knows how easily.

But the small number of known cases is actually one of the important things about this finding.

It signifies that scientists may have found an emerging disease very soon after it made its jump from whatever species it came from into humans. We'll come back to its most likely origins a little later.

The reason for thinking Bas-Congo only recently began infecting humans is that researchers have run blood tests on people throughout the DRC and found no evidence of antibodies that would indicate any of them has been exposed to the new virus.

"It doesn't appear to be widespread throughout the Congo," study co-author Charles Chiu of the University of California San Francisco told Shots. He says the team is planning to do more blood tests on people in the DRC and neighboring countries, such as Congo-Brazzaville right next to Bas-Congo province.

"I would say we caught it fairly quickly," said another study author, Joseph Fair, in a telephone interview from the other side of the DRC, where he's helping to track down the origin of an ongoing outbreak of Ebola hemorrhagic fever that has so far afflicted 51 people and killed 20.

"This wasn't HIV, where we're 15 years into a pandemic before we actually find that we have a pandemic," says Fair, who's with a group called Metabiota that contracts with governments and health agencies to track disease outbreaks.

The three known cases of Bas-Congo fever actually occurred three years ago. But tissue samples from the victims languished in a laboratory freezer in Kinshasa until an astute doctor called the cases to Fair's attention.

That time lag, along with the inability to keep some tissue samples from thawing out, has hampered the researchers' ability to track the virus through other possible cases in Mangala village.

There are some other striking things about the new virus. It doesn't belong to any of the four families of previously known hemorrhagic viruses – Arenaviridae, Bunyaviridae, Filoviridae and Flaviviridae. These families harbor such notorious bugs as Ebola, Marburg, Lassa fever, Crimean-Congo hemorrhagic fever, dengue fever and Rift Valley Fever.

Instead, Bas-Congo belongs to the Rhabdovirus family, which has never been known to include human hemorrhagic fever viruses, although it does contain one that affects fish.

"That in itself is astonishing," Chiu says, "but even within the rhabdovirus family, it's very divergent." That is, it doesn't resemble any other rhabdovirus.

And where did it come from? That's still a mystery, but one clue is that its closest relatives are insect viruses. So researchers are trapping mosquitoes, sandflies, ticks and other insects to see if they can find where Bas-Congo virus hangs out when it's not threatening humans.

The discovery of Bas-Congo is only the latest instance of a powerful new-ish technology that is proving crucial in the identification and characterization of new infectious organisms. It's called deep sequencing, and it allows scientists to spell out the millions of nucleotide sequences in any new microbe without reference to those of known pathogens.

Deep sequencing was also used recently to characterize the new coronavirus that has infected two men in Saudi Arabia (and possibly others).

Once scientists have their hands on the complete genome of these new organisms, they can place it on the right family tree relative to known microbes, providing crucial clues on where it may have come from and what species it likes to infect.

They can also, as in the case of the Saudi virus and Bas-Congo, make diagnostic tests to see who else has been infected. "By knowing the genetic identity, now we will add this to our battery of tests for hemorrhagic fever cases that come in," Fair says.

"Up to 20 percent of hemorrhagic fever outbreaks in the Congo don't have a diagnosis," Chiu says. "They test negative for Ebola, Marburg and everything else. So I suspect there are several other viruses out there that have yet to be discovered."

Fair is confident they will be found, thanks to new technologies – from rapid-throughput gene sequencing to solar power to run freezers. He foresees a new chapter in the detection of emerging diseases "right when they start."

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