Filoviridae
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 Marburg virus particles, ~100,000x magnification |
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Filoviruses are viruses belonging to the family Filoviridae, which is in the order Mononegavirales. These viruses are single stranded negative sense RNA viruses that target primates. There are two general viruses, the Ebola virus (Ebolavirus, with four species) [1] and the Marburg virus (Marburgvirus).
These viruses cause horrific viral hemorrhagic fevers, characterized by bleeding and coagulation abnormalities including diffuse bleeding. Ebola destroys the immune system in an explosive manner. Marburg virus typically has a mortality rate of at least 25%, while Ebola virus, depending on the species, has a mortality rate of anywhere from 50% to 90%. The virus is spread through bodily fluids. They are classified by the Centers for Disease Control and Prevention as Biosafety Level 4. This means that they are among the most lethal and destructive viruses known to man.
The virions (viral particles) are characteristically shaped as long, cylindrical, filamentous particles which may be straight, curved, coiled, or found in a "6" or "U" shaped configuration. They are occasionally branched and the particles vary greatly in length but the diameter (about 80nm) is consistent.
They are produced by budding from an infected cell, and consist of the viral RNA strand and proteins encapsulated in a lipid membrane formed from the host cell's plasma membrane.
The inability of the immune system to clear these viruses may, at least in part, be due to the complex synthesis of a viral glycoprotein which forms heterotrimeric spikes within the virions plasma membrane. The gene encoding this contains a stop codon and as such two forms of the precursor can be produced via a frame shift during translation. These precursors then undergo proteolytic cleavage to form GP1 and GP2 which are also glycosylated before forming the expressed trimer. This results in a variety of epitopes which may result in a less focused immune response that simply doesn't have the time to clear the infection before the organism succumbs. Another virally expressed protein recognised by the immune system is VP40 which is normally expressed on the membrane complexed to VP24.
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