Sep 28, 2012 (CIDRAP News) – Researchers have identified a new virus that can cause hemorrhagic fever in humans, based on their investigation of an unusual outbreak in the Democratic Republic of Congo (DRC) in 2009 that sickened three people, killing two.
The analysis of a virus from the surviving patient—a nurse who cared for the two children who died—revealed some unusual features. Named Bas-Congo virus after the remote tropical rain forest area of the DRC where the outbreak occurred, it is a rhabdovirus closely related to the rabies virus, a family that until now hasn't been known to cause hemorrhagic fever that can quickly kill infected humans.
An international research team described the findings yesterday in Public Library of Science (PLoS) Pathogens.
Though the outbreak bore some of the hallmarks of a hemorrhagic disease outbreak, including spread of the virus to a healthcare worker, the spread of the disease was limited and not accompanied by animal die-offs other unusual events.
The two children who died were from the same village, attended the same school, and lived in the same neighborhood. The first patient was a 15-year-old boy who started having hemorrhagic symptoms with watery diarrhea, but no fever or respiratory symptoms, on May 24. He died 2 days later.
The second patient was a 13-year-old girl who started having similar hemorrhagic symptoms on Jun 5 and was treated by a nurse for a possible malaria infection. Initially she seemed to improve but died 3 days after her symptoms first surfaced.
Patient three is a 32-year-old male health center nurse who treated the sick children. His hemorrhagic disease symptoms began on Jun 13, and a few days later he was transferred to a regional hospital in Boma. There his medical team obtained serum samples and gave him a transfusion, fluid resuscitation, and empiric antibiotic treatment.
Testing found that the virus in the nurse's serum sample was negative for all known to cause hemorrhagic fever in African countries. Genetic sequencing revealed a novel, highly divergent rhabdovirus, but researchers weren't able to culture the virus isolated from the patient's serum, according to the study. Serum samples weren't available for the two children.
Follow-up of patient contacts for 21 days revealed no other hemorrhagic infections.
To explore if the virus is infectious in humans, in early 2012 researchers conducted blood tests on the surviving patient along with five healthcare worker contacts. Not surprisingly, tests showed that the nurse who recovered had been exposed; however, they also found evidence of an asymptomatic infection had occurred in another nurse, suggesting along with the epidemiologic investigation limited human-to-human transmission.
Researchers didn't find the virus in other serum samples from unknown cases or outbreaks of hemorrhagic fever in the DRC from 2008 through 2010. A serum study of 50 random blood donors in Kasai-Orientale province in the central part of the DRC also didn't reveal any evidence of infection with the Bas-Congo virus.
Given the small size of the outbreak, researchers wrote that they doubted the source of the virus was waterborne or airborne, and they noted that there were no animal die-offs that would suggest a likely wild animal or livestock source. The observations suggest a possible arthropod source, such as biting midges.
More tests are under way in the region, including a seroprevalence survey in humans and investigations aimed at finding the source of the virus in arthropods or mammals.
Researchers from the University of California at San Francisco (UCSF) who were part of the study group said the virus could cause future outbreaks. It added that the team is working on new diagnostic tests to identify the disease quickly if it emerges again, according to a UCSF press release yesterday.
Grard G, Fair JN, Lee D, et al. A novel rhabdovirus associated with acute hemorrhagic fever in central Africa. PLoS Pathog 2012 Sep 27 [Full text]
Sep 27 UCSF press release