Ebola Transmission: Difference between revisions
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Revision as of 13:52, 18 April 2013
Introduction
The Ebola virus is a relatively recently described, severe disease-causing pathogen that poses a huge threat to human health mostly within central Africa. This is, in part, due to its high mortality4 and lack of affordable treatment options. Ebola is considered a Biosafety level 4 (BSL-4) agent; classifying it among the most threatening pathogens that exist in the world today. Agents within this category pose severe threats to human health and can be fatal due to the lack of available vaccines and/or treatment options. There are five known Ebola species within the family Filoviridae, four of them endemic to Africa[6], and all of the species within the family cause varying degrees of viral hemorrhagic fever illnesses.[4]
Virology
Structure
The Ebola virus has nonsegmented negative RNA strand genome, which codes for at least seven proteins, enclosed in a nucleocapsid[3]. Four of the virus’ proteins are thought to comprise the capsid that allows the virus to survive in environments while it is not infecting hosts. The capsid allows the transcription and the translation of the viral genome and is therefore the principle player in the virus’ pathogenicity[4].
The virus has many long rods and is much longer than it is wide and is often photographed in a hooked or curved form. The virus is around 80nm in diameter and can be of varying lengths ranging from 600-1400nm[1]. The virus has been known to infect many different cell types including monocytes, macrophages, dendritic cells, liver cells, and endothelial cells, making it a superior infectious agent.
Infection Method
Ebola seems to be spread through direct contact with individuals, dead or alive, who possess the pathogen. In recent study it has been indicated that the Ebola virus has developed several customized ways to enter host cells depending on the virus' size and what kind of cell the virus wants to gain access to[1]. However, it seems in most cases the virus prefers to use macropincytosis, a form of endocytosis, to gain preliminary access. The virus requires a special cholesterol transporter known as Niemann-Pick C1 (NPC1) to successfully enter a cell and seems to be tied to the release of the genome into the host cell[8]. Ebola infects a wide range of cells but the most common are mononuclear phagocytes, hepatocytes, and endothelial cells. The virus has been shown to impair the immune function of the body when it infects the phagocytic cells by way of interfering with the neutrophils of the body and thus contributing its high mortality rate9. Like most pathogenic agents, the functionality of a host cell is disrupted by the presence of Ebola and eventually the virus takes over all cell function to produce only more viral copies.
Exiting Strategy
Once inside of a cell Ebola does not produce its own cell membrane and instead steals some of its host membrane to survive. [4][2]The nucleocapsid and viral proteins move to new sites of infection and form themselves into virons where they can then go on to infect around the host body.
Pathogenesis
Transmission
In the past it was thought that the virus only infected and caused death
in humans and non-human primates mostly in the central African region.
The disease has been known to spread from human to human by way of
contaminated bodily fluids which happens to be more common in developing nations.
Additionally, the main reservoirs of infection was
thought to be the fruit bat[6]. But, in recent years, as more
study is being conducted on the virus, it seems that there is more to its
complex interactions among multiple species. It was found that Ebola can, and does, infect pigs and can pass on to nonhuman primates.[6] This is an early sign that pigs may play a role in human infection processes. However, in the pig the virus seems to be airborne, a dramatic change from what was previously known about the disease. This has far reaching consequences for treatment and containment.[6]
Containment
Due to its classification as a level four safety agent, studying
Ebola in the lab is no small feat. The virus is not only well adapted
to infect its hosts, but also excels at spreading from host to host.
Scientists who choose to work with
Ebola must use the utmost caution to prevent the virus' ability to infect
them while they conduct their experiments. Full hazard suits must be
worn at all times and each suit is throughly examined before entering
a containment space.
Conclusion
In today's world Ebola is still a huge problem that faces many developing nations within Africa. In 2012 alone there were 5 outbreaks of Hemorrhagic Fevers around the world and 3 of them were due to the Ebola virus.7 One of the factors that makes this disease so clinically challenging is the fact that it is indistinguishable from other agents that cause alternative forms of hemorrhagic fevers[3]. Because some of these diseases are treatable doctors in at risk areas must depend on detailed patient history accounts which can be a roadblock due to language barriers.
The best way to move forward from the pain caused by all of the species of Ebola is to continue research on promising single-step vaccines and begin to move them into human trial stages. The fact that some strains of Ebola can have up to an 88%[3][5] mortality rate should be enough of an incentive to push research forward. In addition, the world as a whole needs to start to get serious about ways to make affordable, life-saving vaccinations available to those who need them most.
References
3. "Ebola virus: from discovery to vaccine". Nature Reviews Immunology 3. 2003. p. 667- 85.
7.
Edited by (Victoria Rose Gawlik), a student of Nora Sullivan in BIOL187S (Microbial Life) in The Keck Science Department of the Claremont Colleges Spring 2013.
