Ebola Virus Antigens

Ebola virus (EBOV) is one of five known viruses within the genus Ebolavirus, belongs to the family Filoviridae. Ebola virus is a highly pathogenic and highly lethal virus that can cause human and primate Ebola haemorrhagic fever, known as Ebola virus disease (EVD). The natural host for the virus is unknown, but fruit bats have been suggested as the natural reservoir. EBOV can be transmitted through body and body fluid contact. There are 4 subtypes of EBOV: EBV-Z, EBV-S, EBV-R and EBV-C. The lethality of Z type and S type to human and primate is very high while R type is more moderate. There is serological cross-reactivity between the four subtypes.

EBOV is a filamentous shape virus with dimensions of 800 nm long and 80 nm in diameter. There are three layers of the virus: the nucleocapsid, the matrix space and the envelope. EBOV has one molecule of linear, single-stranded, negative-sense RNA, 18,959 to 18,961 nucleotides in length. The genome of EBOV codes for seven structural proteins, including the nucleoprotein (NP), virion protein (VP) 35, VP40, glycoprotein (GP1,2), VP30, VP24, and the RNA-dependent RNA polymerase (L).

The role of structural proteins is summarized as follows:

• NP Essential for RNA encapsulation
• GP Essential for the attachment of the virus to the host cell membrane and entering the nucleocapsid of the virus into the host cytoplasm
• VP24 Essential for virus assembling and in transcription by being a part of the nucleocapsid structure
• VP30 Suppression of viral RNA silencing
• VP35 Binds to NP to remove the nucleocapsid to facilitate the transcriptional expression
• VP40 Required for virus localization out of the host cell membrane and gives filamentous shape to virus together with GP and helps maintain the structural integrity of the virion

Figure 1. Viral proteins implicated in the pathogenesis of EBOV. (Ndayambaje, 2024)

The life cycle of EBOV is thought to begin with a virion attaching to specific cell-surface receptors such as C-type lectins, DC-SIGN, or integrins, and the virus structural glycoprotein (known as GP1,2) is responsible for the virus' ability to bind to and infect targeted cells. After attachment to the plasma membrane, EBOV envelope and cell membrane fuse through micropinocytosis instead of classic clathrin or caveolin mediated endocytosis pathways. The virions taken up by the cell then travel to acidic endosomes and lysosomes where the viral envelope glycoprotein GP is cleaved and the viral nucleocapsid is released into the cytoplasm. Encapsidated, negative-sense genomic ssRNA is used as a template for the synthesis (3'-5') of polyadenylated, monocistronic mRNAs and, using the host cell's ribosomes, tRNA molecules, etc., the mRNA is translated into individual viral proteins. Newly synthesised structural proteins and genomes self-assemble and accumulate near the inside of the cell membrane. Mature progeny ribonucleoprotein complexes and viral proteins are transported to the plasma membrane, where particle budding occurs.

Fig 2. Life cycle of Ebola virus²

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