How does the Ebola Virus Overcome the Immune System?

With average fatality rates ranging from a terrifying 25-90%, the Ebola Virus is one of the deadliest viruses known to mankind. The key aspect focused on in this article is that of the complications of the Ebola Virus Disease, exploring the way in which the virus hijacks the body’s immune system. This article will also outline the transmission and symptoms of the disease and briefly illustrate the structure of the virus itself, shedding light on exactly how this disease is so detrimental to the body.

The Ebola Virus Disease (EVD), previously identified as Ebola haemorrhagic fever first appeared in 1976 in 2 simultaneous outbreaks: 1 in Nzara, South Sudan and 1 in Yambuku in the Democratic Republic of Congo. Since then, the 2014-2016 outbreak in West Africa has been the largest Ebola outbreak. The current 2018-2020 outbreak in eastern DRC is extraordinarily complex and has so far, a death rate of a tremendous 66%. These figures clearly show the severity of the EVD.

From the image shown, we can see the structure of the Ebola Virus. The outer envelope is covered in small spikes, made of virally encoded glycoproteins. These spikes allow it to attach itself to host cells. The virus consists of an antisense RNA virus (does not encode mRNA) enclosed in a capsid known as the nucleocapsid, creating a helical complex. It requires a polymerase transformation to reproduce. This leaves the virus subject to genetic code errors, thus creating many subtypes of Ebola.

The nucleocapsid is formed by viral proteins and the space between the outer viral envelope and the nucleocapsid is known as the matrix space. The Ebola matrix protein shapes the virus and drives the process of budding. In addition, there is another viral protein in the Ebola virus’ structure know as VP24. The function of the protein is to primarily inhibit a signaling pathway known as JAK-STAT. The JAK-STAT signaling pathway is a chain of interactions between proteins in a cell and is involved in processes such as orchestrating the immune system, cell division, cell death and tumour formation. By inhibiting this signaling pathway, several cellular activities are disrupted including transcription.

The Ebola Virus is from the virus family Filoviridae and the 3 types of Ebola virus strains known to cause fatality are Ebola-Zaire, Ebola-Sudan and Ebola-Cote’d Ivoire, affecting both human and non-human primates such as monkeys. The fruit bats of the Pteropodidae family are considered to be Ebola virus hosts and from them, Ebola is introduced into the human population through close contact with bodily fluids of infected animals. Ebola virus particles occupy an infected person’s blood and other bodily fluids, which can enter another person through the eyes, mucus membranes, scratches on the skin or from hypodermic needles (but not from the air or from insects). Moreover, bodies of people who have died of Ebola are highly infectious.

Upon entering the body, the virus targets many types of immune cells which represent the first line of defence against attack. These include dendritic cells, which normally display signals of an infection on their surfaces to activate T-lymphocytes. These white blood cells would normally destroy other infected cells before the virus replicates further. With defective dendritic cells failing to give the right signal, The T-cells don’t respond to the infection, and neither do the antibodies that depend on them for activation. As a result, the virus will start replicating rapidly. Furthermore, the virus attacks immune cells in the blood stream, which carry the infection to the liver, spleen and lymph nodes. Ebola also blocks the release of interferon, a protein made by immune cells used for fighting viruses.

As a result of the virus travelling through the blood to new sites, it creates a lot of trouble in the bloodstream. Macrophages eat up the virus and hence become infected. Consequently, they release proteins that cause small clots to form in the bloodstream, reducing and eventually blocking blood flow to vital organs such as the liver and kidneys. They also produce inflammatory signaling proteins and Nitric Oxide which damage the inner lining of blood vessels, causing their leakage. Due to this, RBCs will break apart when moving through small vessels filled with clots. The spleen, for example, will become overwhelmed with broken blood vessels. This demonstrates the haemorrhaging effect of the Ebola virus.

From the information above, we can vividly understand the way in which the Ebola Virus works to break down the body’s immune system. Now, we will consider the bodily effects of the virus, with regards to the symptoms and key details for survival.

The incubation period of the virus extends from 2-21 days, but usually takes 4-10 days before symptoms appear. Considering the strategic method of attack of the virus, we can link the symptoms observed. As we have seen, the Ebola virus damages many kinds of tissue in the body, either by direct infection of the virus or by the body’s extreme inflammatory response. The adrenal glands (above the kidneys) breakdown, leading to dangerously low blood pressure and a decreased ability to produce steroid hormones. Fluid accumulates in the brain and this can result in seizures and convulsions. Those people who die from EVD succumb to very low blood pressure, multiple organ failure and the shock of severe infection. We can understand from this how the Ebola Virus Disease can lead to a multiple system collapse.

In conclusion, we have looked at the Ebola Virus as one of the most lethal viruses known. We have seen how it manipulates the body’s immune system by disabling key signaling pathways and inhibiting the release of the very protein, which is made by immune cells, meant to fight off viruses. Despite its containment, in the absence of effective treatment, the Ebola virus still poses a significant threat to both humans and animals, therefore prevention of a worldwide outbreak lies in the hands of education with regards to the virus, gathering knowledge and acting effectively.

-Afrin Jubair Ali