Bas-Congo virus

Bas-Congo virus is a single-stranded negative-sense RNA virus. It is a member of the Rhabdoviridae family and is phylogenetically related to members of the Tibrovirus genus. Rhabdoviruses are a large and ecologically diverse family of viruses. They are capable of infecting plants, insects, fish, reptiles, birds, marsupials, and placental mammals, including humans. The majority of rhabdoviruses are transmitted by insects (i.e., arthropod-borne). Prototypical rhabdoviruses, such as Rabies and Vesicular Stomatitis virus, have simple genomes consisting of five genes. The morphology of Rabies and VSV resembles a bullet shape.

Bas-Congo virus was discovered in the plasma of a 32-year-old male who recovered from an illness with symptoms resembling hemorrhagic fever. The virus was discovered after testing was performed to exclude several viral agents suspected of causing hemorrhagic fever. RNA copies of BASV were found in the serum of the lone survivor using next-generation sequencing.

Two people, a surviving nurse and a close contact, developed antibodies highly specific for the BASV glycoprotein (BASV-G). Neutralization was observed only with BASV-G and not with pseudoviruses carrying the glycoprotein of the related rhabdovirus vesicular stomatitis virus (VSV-G) thus indicating that BASV was the actual cause of the outbreak.

The discovery of a rhabdovirus associated hemorrhagic fever in humans was unexpected because no rhabdovirus has ever been associated with hemorrhagic fever in humans. However, fish can suffer from viral hemorrhagic septicemia, a disease caused by a member of the genus Novirhabdovirus that leads to bleeding. The most relevant rhabdovirus genera to humans are: Lyssavirus causing rabies and Vesiculovirus causing an unpleasant but non-fatal flu-like disease.

Phylogenetic analysis of the polymerase protein (L) revealed indicated that the virus was most closely related to members of the tibrovirus genus. Tibroviruses are poorly characterized and not well-understood. There are eight known tibroviruses, including BASV [2]. Four tibroviruses have been isolated from biting midges (Culicoides), three from humans, and one from a healthy steer. With the exception of Bas-Congo, none of the other tibroviruses have been associated with any disease. Experimental infection of cattle with various tibroviruses does not produce any symptoms of disease[3].

The disease associated with Bas-Congo virus is a severe acute hemorrhagic fever characterized by rapid disease progression. However, there are clues to asymptomatic infections as well. The onset is sudden, symptoms include high fever, malaise, nausea, vomiting, diarrhea, abdominal pain, headache and fatigue. Blood loss appears very early in the course of the disease, including nose bleeds, mouth bleeding and hematemesis. In the 2009 outbreak, death occurred two or three days after the onset of symptoms, suggesting the virus to be more virulent than even the marburg virus.

The first patient in Mangala village was a 15-year-old boy attending the local school. He died two days after he became ill. A 13-year-old girl attending the same school developed symptoms a few days later and died three days thereafter. The two students were in different classes and had no evident personal contact in the weeks before the outbreak. The source of primary infection remains unknown. A male nurse working in the local health center visited by the first victims showed signs of the disease 9 days after the girl's death. This indicates human-to-human transmission of BASV through body fluids and close contact; transmission through aerosol would most likely result in more cases.

A fourth person directly caring for the nurse developed antibodies against BASV but remained asymptomatic.