More filoviruses in bats

The family of viruses known as the Filoviridae (filo, from the Latin for thread) is well known for the ebolaviruses, which cause the hemorrhagic disease that regularly erupts in Africa. As Earth€™s virome is slowly revealed, other filoviruses are discovered.

The first filovirus discovered was Marburg virus, first described in 1967 in Germany when grivet monkeys transmitted the virus to humans. Next came Ebola virus which infected humans in 1976. Other species of ebolaviruses have since been discovered, including Bundibugyo ebolavirus, Reston ebolavirus, Sudan ebolavirus, and Tai Forest ebolavirus. LLoviu virus (actually only the genome sequence, not infectious virus) was discovered in Spanish cave bats  in 2011. In 2018 filovirus sequences were identified in fish, in insectivorous bats in Sierra Leone, and in bats in China. One of the latter is called Mengla virus after its place of discovery. While no infectious Mengla virus has been isolated, near full length genome sequence was obtained from the liver of a bat, enabling a variety of experiments that shed light on the biology of this virus (link to paper).

Glycoproteins present in viral envelopes play many important roles in infection, including binding to cell receptors. Because no Mengla virus was available, instead the viral glycoprotein was inserted in the place of the vesicular stomatitis virus glycoprotein. Such viruses, called pseudotypes, allow the study of the Mengla virus glycoprotein without having infectious virus. The VSV pseudotyped virus with the Mengla virus glycoprotein required NPC1 to enter human cells, just like other filoviruses. NPC1 is an endosomal protein required for fusion of the viral and cell membranes.

These pseudotyped viruses could infect cells from a wide range of animals, including humans, monkeys, hamsters, and dogs, just like viruses harboring the glycoproteins of ebolaviruses or Marburg virus. This result means that Mengla virus might be able to cross species barriers as do ebolaviruses and Marburg virus.

Of course, the ability of a viral glycoprotein to mediate entry into cells does not mean that the entire viral reproduction cycle will take place. To partly address this question, Marburg virus and Ebola virus minigenomes were made, consisting only of the left and right ends of the viral genomes. These mini genomes could multiply in cells containing Mengla virus replication proteins. Again, the entire virus reproduction cycle was not examined, but the results are an indication that Mengla virus proteins can function in human cells and replicate the genomes of other ebolaviruses.

Epidemics of Ebola virus disease are thought to begin when humans contact bushmeat contaminated with the virus. Whether any of the other filoviruses recently discovered, including Mengla virus, pose similar threats is unknown.

Phylogenetic analysis of the Mengla virus genome reveals that it is a member of a new genus within the filovirus family, tentatively called Dianlovirus. At the moment, the filovirus family consists of the following genera: Marburgvirus, Ebolavirus, and Cuevavirus. There are likely to be more.