Beatrice Hill Virus Represents a Novel Species in the Genus Tibrovirus (Mononegavirales: Rhabdoviridae)

Human Tibroviruses: Commensals or Lethal Pathogens?

Rhabdoviruses are a large and ecologically diverse family of negative-sense RNA viruses (Mononegavirales: Rhabdoviridae). These viruses are capable of infecting an unexpectedly wide variety of plants, vertebrates, and invertebrates distributed over all human-inhabited continents. However, only a few rhabdoviruses are known to infect humans: a ledantevirus (Le Dantec virus), several lyssaviruses (in particular, rabies virus), and several vesiculoviruses (e.g., Chandipura virus, vesicular stomatitis Indiana virus). Recently, several novel rhabdoviruses have been discovered in the blood of both healthy and severely ill individuals living in Central and Western Africa. These viruses—Bas-Congo virus, Ekpoma virus 1, and Ekpoma virus 2—are members of the little-understood rhabdoviral genus Tibrovirus. Other than the basic genomic architecture, tibroviruses bear little resemblance to well-studied rhabdoviruses such as rabies virus and vesicular stomatitis Indiana virus. These three human tibroviruses are quite divergent from each other, and each of them clusters closely with tibroviruses currently known only from biting midges or healthy cattle. Seroprevalence studies suggest that human tibrovirus infections may be common but are almost entirely unrecognized. The pathogenic potential of this diverse group of viruses remains unknown. Although certain tibroviruses may be benign and well-adapted to humans, others could be newly emerging and produce serious disease. Here, we review the current knowledge of tibroviruses and argue that assessing their impact on human health should be an urgent priority.

Human, Nonhuman Primate, and Bat Cells Are Broadly Susceptible to Tibrovirus Particle Cell Entry

In 2012, the genome of a novel rhabdovirus, Bas-Congo virus (BASV), was discovered in the acute-phase serum of a Congolese patient with presumed viral hemorrhagic fever. In the absence of a replicating virus isolate, fulfilling Koch's postulates to determine whether BASV is indeed a human virus and/or pathogen has been impossible. However, experiments with vesiculoviral particles pseudotyped with Bas-Congo glycoprotein suggested that BASV particles can enter cells from multiple animals, including humans. In 2015, genomes of two related viruses, Ekpoma virus 1 (EKV-1) and Ekpoma virus 2 (EKV-2), were detected in human sera in Nigeria. Isolates could not be obtained. Phylogenetic analyses led to the classification of BASV, EKV-1, and EKV-2 in the same genus, Tibrovirus, together with five biting midge-borne rhabdoviruses [i.e., Beatrice Hill virus (BHV), Bivens Arm virus (BAV), Coastal Plains virus (CPV), Sweetwater Branch virus (SWBV), and Tibrogargan virus (TIBV)] not known to infect humans. Using individual recombinant vesiculoviruses expressing the glycoproteins of all eight known tibroviruses and more than 75 cell lines representing different animal species, we demonstrate that the glycoproteins of all tibroviruses can mediate vesiculovirus particle entry into human, bat, nonhuman primate, cotton rat, boa constrictor, and Asian tiger mosquito cells. Using four of five isolated authentic tibroviruses (i.e., BAV, CPV, SWBV, and TIBV), our experiments indicate that many cell types may be partially resistant to tibrovirus replication after virion cell entry. Consequently, experimental data solely obtained from experiments using tibrovirus surrogate systems (e.g., vesiculoviral pseudotypes, recombinant vesiculoviruses) cannot be used to predict whether BASV, or any other tibrovirus, infects humans.

Taxonomy of the order Mononegavirales: update 2018

In 2018, the order Mononegavirales was expanded by inclusion of 1 new genus and 12 novel species. This article presents the updated taxonomy of the order Mononegavirales as now accepted by the International Committee on Taxonomy of Viruses (ICTV) and summarizes additional taxonomic proposals that may affect the order in the near future.