The current outbreak of Ebola in Central Africa is the largest the world has ever seen. As of mid-August 2014, the death toll is nearing 1000 and the disease has spread more rapidly and widely through African nations than any previous outbreak. The disease has several strains which have fatality rates of between 50-90%. Yet the virus is fragile and is killed by disinfectants and even soaps – so why is it so deadly? The answer partially lies in the virus’s ability to evade the human immune system.
An example of the virus causing problems for human immunity is its ability to block the actions of interferons, chemical messengers which can block viral replication, thereby slowing or preventing them from infecting body cells. In the presence of interferons, transcription factors called STAT1 and 2 are usually transported to the cell nucleus to regulate transcription of antiviral proteins. But the Ebola virus produces a protein called VP24, which competes with the carrier proteins which the STAT proteins bind to. The STAT proteins are not transported to the nucleus, and essential virus-fighting proteins are not produced.
VP35, another protein produced by the Ebola virus, competes with interferons to bind to RIG-1, a sensor which alerts the rest of the cell that a virus is present in the body. By binding with RIG-1, VP35 stops interferons from signalling cells to produce more antiviral products. In these and many other ways, the Ebola virus prevents the body’s normal immune response, causing serious illness and death in a significant proportion of the humans it infects.
Development of drugs to combat Ebola is difficult because it is a viral disease which has originated from an animal, believed to be fruit bats. Experimental drug ZMapp – a serum of monoclonal antibodies harvested from mice infected with the virus – has shown promising results. However, developing treatments or vaccines for Ebola is not financially viable for drug companies; the disease is confined to the developing world and the vast majority of its sufferers do not have the means to pay for treatment. It is likely to be governments that will pick up the bill for the cost of developing and distributing new drugs, which could have the potential to stop this deadly disease in its tracks.