Filovirus - Introduction, Characteristics, Morphology, Genome

Classification of Filovirus

Filovirus is classified as:

Realm: Riboviria

Kingdom: Orthornavirae

Phylum: Negarnaviricota

Class: Monjiviricetes

Order: Mononegavirales

Family: Filoviridae

The family Filoviridae includes several genera such as:

• Cuevavirus - Lioviu cuevavirus is the only species in this genera

• Dianlovirus - Mengla dianlovirus is the only species in this genera

• Ebolavirus - Ebola virus (EBOV)

• Marburgvirus - Marbury virus (MARV)

• Striavirus

• Thamnovirus

Species of Filovirus

Filoviruses cause severe hemorrhagic fever in human and non-human primates.

The genus Ebolavirus is subdivided into 4 species of filovirus on the basis of serological cross-reactivity and genetic differences. i.e.

• Zaire ebolavirus (ZEBOV)

• Sudan ebolavirus (SEBOV)

• Taï Forest ebolavirus / Cote d’Ivoire (CIEBOV)

• Reston ebolavirus (REBOV)

• Bombali ebolavirus

• Bundibugyo ebolavirus (BEBV) = previously BEBOV

The genus Marburgvirus contains three species:

• Lake Victoria Marburgvirus (MARV) previously known as Marburg marburgvirus = the case fatality rate is 90%

• Marburg virus

• Ravn virus

Morphology of Filovirus

Morphologically, Filoviruses are filamentous, enveloped particles a with non-segmented, negative-sense RNA genome of 19kb in length. They are uniformly 80nm in diameter while the length varies from 800-14,000 nm. As they are filamentous, can appear “U” or “6” shaped, circular, or branched.

Genome

In its genome, Filoviruses possess a central helical core known as ribonucleoprotein complex (RNP), composed of NP, VP35, VP30, L, and the viral RNA. The GP1 and GP2 project 10 nm from the surface (glycoprotein is secreted dimer). The matrix proteins VP40 and VP24 underlie the membrane

The gene order is:- 3’leader, NP, VP35, VP40, GP, VP30, VP24, L, 5’ trailer.

• NP = nucleoprotein

• GP = Glycoprotein

• VP = Virion protein

• L = Polymerase protein

NP- Nucleoprotein

• NP - nucleoprotein is the major structural phosphoprotein and only the phosphorylated form is incorporated into virions

• the major component of RNP

GP- Glycoprotein

• GP- Glycoprotein is directed into the endoplasmic reticulum by an N-terminal hydrophobic domain which is cleaved by signal peptidases

• It mediates binding to cellular receptors and subsequent fusion with cellular membranes

• It is a major viral Ag

L-Large protein/polymerase protein

• L-Large protein/polymerase protein is regarded as RNA-dependent RNA polymerase even though transcriptase and replicate activities have not been demonstrated

Virion proteins

VP35 and VP30 (structural proteins)

• They are components of RNP but the association of VP35 is weak compared with NP and VP30

• Ebola VP30 is a minor (2^nd) structural phosphoprotein of viruses where as VP 35 is not.

VP40 and VP24

• They are membrane-associated and not associated with RNP

• VP24 serves as 2^nd matrix protein and links other membrane proteins to RNP

• VP 40 is the driving force behind virus particle formation