Ebola virus disease or EVD is a severe illness caused by ebolaviruses affecting humans and other primates. Often fatal due to the presence of high-grade fever and severe hemorrhaging, EVD has caused numerous so-called Ebola outbreaks in remote villages in Central Africa, as well as major urban areas in Western Africa.
Also simply known as Ebola, the disease is curable but can still be very dangerous fatal. Note that deaths from influenza remain higher than Ebola. Furthermore, the influenza virus is transmitted airborne while ebolaviruses are transmitted only via direct contact with body fluids such as blood and other secretions.
Nonetheless, deaths from EVD have been regarded as horrific because of how the relevant virus attacks and destroys the human body. But why exactly Ebola is so deadly? How does the Ebola virus affect and destroy the body?
Major Reasons why Ebola can be Deadly
1. The Ebola Virus Attacks the Immune System
Upon direct contact with a body fluid from an infected person, the virus enters the human body via the eyes, nose, mouth, or broken skin and attacks the internal organs and bodily systems, including the immune system. The problem actually starts with the Ebola virus impairing the immune response.
Ebola virus attacks and replicates in different immune cells, including dendritic cells, which act as messengers between innate and adaptive immune responses. Furthermore, dendritic cells activate other immune cells such as Killer T cells and Helper T cells that are responsible for containing viral infections.
Infected dendritic cells also cause T cells to kill themselves prematurely by sending signal proteins to initiate programmed cell death. Nonetheless, an attack on the dendritic cells would leave the immune system unable to function properly due to lack of communication.
Remember that the Ebola virus also attacks other immune cells. For instance, it attacks and replicates on natural killer cells. These cells are also responsible for responding to viral infections. However, Ebola virus hurriedly attacks these cells even before they can react. The virus also attacks macrophages and monocytes.
2. Replication of the Ebola Virus is Rapid and Efficiently
One of the reasons why Ebola can be very deadly is that it replicates rapidly and efficiently. For starters, the virus is acellular. It uses virally-encoded and host-encoded enzymes and self-assembles host resources such as cell structures to replicate inside an infected cell. Because Ebola virus is part of the filovirus taxonomy, it replicates efficiently.
It is also worth noting that Ebola does not attack a single organ or system in the human body. Instead, it attacks multiple organs and systems at once, particularly the immune system and the liver, while also replicating relentlessly.
Remember that the virus impairs the immune response of the body by attacking immune cells. This impairment allows unmonitored replication and proliferation. Furthermore, when it attacks immune cells such as dendritic cells and natural killer cells, they replicate millions of copies for each infected cell.
The infected immune cells carry the virus further to the nearby lymph nodes in which further replication takes place. From the lymph nodes, the virus enters the bloodstream and lymphatic system, thus spreading further throughout the body. The virus also attacks and replicates in other organs such as the liver.
3. Ebola Virus Disease Can Cause Internal and External Hemorrhages
What makes EVD both deadly and horrifying is that it can cause internal and external hemorrhages or bleeding in some cases. Note that once it enters the body and starts attacking multiple organs and systems at once, the extent of hemorrhaging can be expansive across the body.
The root cause of excessive hemorrhaging remains unclear. One theory is that it stems from how the virus attacks macrophages and monocytes. Once infected, these cells signal the specific cells in the blood vessels to release fluids. Ebola virus and the infected macrophages and monocytes also activate specific immune cells called neutrophils. The activation signals further the blood vessels to release more fluid, thus resulting in internal bleeding.
Another theory of the hemorrhagic feature of some EVD cases states that internal and external bleeding result from how the virus disrupts the functioning of the immune systems. The entire system goes out of control as several types of immune cells become infected, thus triggering inflammatory responses that affect the clotting capabilities of the body.
It is still worth mentioning that bleeding is not a universal feature of this disease. Majority of documented people with EVD did not manifest hemorrhagic symptoms. In addition, bleeding transpires in the late stages of the disease, particularly about 24 to 48 hours before the body succumbs to death.
4. The Disease Triggers A Cytokine Storm Immune Response
Ebola causes a variety of painful symptoms to include grave diarrhea, vomiting, and of course bleeding from the inside and to the outside, on top of high-grade fever and bodily pains. Some patients die due to dehydration while others due to overall shock.
The body desperately strives to remain alive as the virus spreads across the body and attacks different organs and systems. As its last-ditch effort, the immune system activates a cytokine storm to kill the viruses and infected cells, and contain the infection.
A cytokine storm is characterized by the overproduction of different types of immune cells and the subsequent over-activation of these cells. It is specifically a form of systematic inflammatory response characterized by the release proteins called cytokines responsible for activating immune cells and signaling them to travel to the site of infection.
The problem with a cytokine storm is that it produces collateral damage. The large number of immune cells might be effective in containing the virus across the body, but these cells also attack other cells, thus damaging other organs in the process.
FURTHER READINGS AND REFERENCES
- Baseler, L., Chertow, D. S., Johnson, K. M., Feldman, H., Morens, D. M. 2017. The Pathogenesis of Ebola Virus Disease. Annual Review of Pathology: Mechanisms of Disease. 12: 387-418. DOI: 10.1146/annurev-pathol-052016-100506
- Bixter, S. L. and Goff, A. J. 2015. The Role of Cytokines and Chemokines in Filovirus Infection. Viruses. 7(10): 5489-5507. DOI: 10.3390/v7102892
- McElroy, A. 2015. Understanding Bleeding in Ebola Virus Disease. Clinical Advances in Hematology & Oncology. 13(1): 29-31. PMID: 25679971
- Rivera, A. and Messaoudi, I. 2015. Pathophysiology of Ebola Virus Infection: Current Challenges and Future Hopes. ACS Infectious Disease. 1(5): 186-197. DOI: 10.1021/id5000426