A piece of genetic detective work by an international team has uncovered a deadly virus not seen before that likely caused a small isolated outbreak of acute hemorrhagic fever in central Africa in the summer of 2009.
The outbreak, in the Democratic Republic of Congo (DRC), killed two people and left one person seriously ill. The researchers have given the deadly pathogen the name Bas-Congo virus (BASV), after the province where the three people lived.
They report their work in the 27 September issue of the online open access journal PLoS Pathogens.
The researchers were in an international consortium comprising the University of California, San Francisco (UCSF), the US company Microbiota, and other institutions and organizations in America and Africa.
The 2009 outbreak of acute hemorrhagic fever started when a 15-year-old boy from a village called Mangala in the DCR suddenly got ill and started bleeding from the nose and gums and vomiting blood. He got worse very quickly and died three days later.
A week later, a 13-year-old girl who went to the same school as the boy, started with the same symptoms, which also worsened rapidly, and she also died within three days.
Then, again, another week after the girl died, a male nurse who had cared for her started with the same symptoms. He was transferred to hospital and survived.
The UCSF team leader was Charles Chiu, assistant professor of laboratory medicine at UCSF and director of the university’s Abbott Viral Diagnostics and Discovery Center. He says in a press release:
“These are the only three cases known to have occurred, although there could be additional outbreaks from this virus in the future.”
Initial tests for known viruses on blood samples taken from the survivor revealed nothing. But eventually, after more members of the consortium got involved, further genetic tests uncovered a completely new virus.
These tests used a new approach called “deep sequencing” that generates millions of sequences of DNA from a clinical sample and then stitches them together using computer algorithms and human analysis.
Chiu says the new virus, BASV, is quite unlike other viruses in Africa known to be behind deadly outbreaks of acute hemorrhagic fever, such as Ebola virus, Lassa virus, and Crimean-Congo Hemorrhagic Fever virus.
Genetically, BASV bears more resemblance to rabies viruses, which cause a different type of infection, a neurological illness that can take months to develop but invariably kills, explains Chiu.
The virus belongs, like rabies, to a family called the rhabdoviruses.
“BASV was present in the blood of the lone survivor at a concentration of over a million copies per milliliter. The genome of BASV, assembled from over 140 million sequence reads, reveals that it is very different from any other rhabdovirus,” write the authors.
No other rhabdovirus is known to cause the acute, rapid and deadly hemorrhagic fever seen in the three cases in the Congo. For example, rabies can be deadly if untreated, but it doesn’t progress in the rapid and deadly fashion seen with BASV.
However, there is some precedent: in fish, where rhabdoviruses are known to cause hemorrhagic septicemia (acute bleeding and death).
When the researchers did an antibody test on the man who survived, and those who had come into contact with him, they concluded while the virus may spread from person to person, the likely source is not in humans, but in another species, such as an insect or rodent. The likely “reservoir” and how the virus spreads from it is still being sought.
Chiu’s team is still working on new ways to diagnose the new virus so that health officials in central Africa can identify it quickly should there be another outbreak.
Joseph Fair, co-author and vice president of Metabiota, says:
“Known viruses, such as Ebola, HIV and influenza, represent just the tip of the microbial iceberg.”
“Identifying deadly unknown viruses, such as Bas-Congo virus, gives us a leg up in controlling future outbreaks,” he adds.
Written by Catharine Paddock PhD