The Ebola VirusA virus is an ultramicroscopic infectious organism that, having noindependent metabolic activity, can replicate only within a cell of another hostorganism. A virus consists of a core of nucleic acid, either RNA or DNA,surrounded by a coating of antigenic protein and sometimes a lipid layersurrounds it as well.
The virus provides the genetic code for replication, andthe host cell provides the necessary energy and raw materials. There are morethan 200 viruses that are know to cause disease in humans. The Ebola virus,which dates back to 1976, has four strains each from a different geographic area,but all give their victims the same painful, often lethal symptoms.The Ebola virus is a member of a family of RNA viruses known as Filoviriade’ and falling under one genus, Filovirus’. “The Ebola virus andMarburg virus are the two known members of the Filovirus family” (Journal of theAmerican Medical Association 273: 1748).
Marburg is a relative of the Ebolavirus. The four strains of Ebola are Ebola Zaire, Ebola Sudan, Ebola Reston,and Ebola Tai. Each is named after the geographical location in which it wasdiscovered.
These filoviruses cause hemorrhagic fever, which is actually whatkill victims of the Ebola virus. Hemorrhagic fever as defined in Mosby’sMedical, Nursing, and Allied Health Dictionary as, a group of viral aerosolinfections, characterized by fever, chills, headache, malaise, and respiratoryor GI symptoms, followed by capillary hemorrhages, and, in severe infection,oliguria, kidney failure, hypotension, and, possibly, death. The incubationperiod for Ebola Hemorrhagic Fever ranges from 2-21 days (JAMA 273: 1748).Theblood fails to clot and patients may bleed from injections sites and into thegastrointestinal tract, skin and internal organs (Ebola Info. from the CDC 2).The Ebola virus has a tropism for liver cells and macrophages, macrophages arecells that engulf bacteria and help the body defend against disease. Massivedestruction of the liver is a hallmark feature of Ebola virus infection.
Thisvirus does in ten days what it takes AIDS ten years to do. It also requiresbiosaftey level four containment, the highest and most dangerous level. HIV thevirus that causes AIDS requires only a biosaftey level of two. In reportedoutbreaks, 50%-90% of cases have been fatal (JAMA 273: 1748).Ebola can be spread in a number of ways, and replication of the virusoccurs at an alarming rate. Ebola replication in infected cells takes abouteight hours. Hundreds to thousands of new virus particles are then releasedduring periods of a few hours to a few days, before the cells die.
The severalcycles of replication occur in a primate before the onset of the fever and otherclinical manifestations (Ornstein, Matthews and Johnson 7). In most outbreaks,transmission from patient to patient within hospitals has been associated withinthe reuse of unsterile needles and syringes. High rates of transmission inoutbreaks have occurred from patients to heath-care workers and to familymembers who provide nursing care without appropriate precautions to preventexposure to blood, other body fluids, vomitus, urine and stool. Risk fortransmitting the infection appears to be highest during the later stages ofillness, which are often characterized by vomiting, diarrhea, shock, andfrequently hemorrhaging (JAMA 274: 374). Even a person who has recovered fromthe symptoms of the illness may have the virus present in the genital secretionsfor a brief period after.
This makes it possible for the virus to be spread bysexual contact. Complete recovery is reached only when no particles of thevirus are left in the body fluids, this however is rarely attained. The disease,for humans, is not airborne, capable to be passed on through air travel, but fornonhuman primates it has been a possibility in a few cases.Ebola Zaire was identified in 1976 in Northern Zaire and was the firstdocumented appearance of the virus. This strain of the virus effects humans andnonhuman primates.
Close contact and dirty needles spread the Ebola virus. Thecenter of the epidemic in Zaire involved a missionary hospital where they reusedneedles and syringes without sterilization. Most of the staff of the hospitalgot sick and died. This outbreak infected 318 with a death rate of 93% (LeGuenno et al. 1271). Another fatal case was reported one year later in Zairebut nothing major ever became of it. The most recent case recorded was theinfamous breakout in Kikwit, Zaire.
This breakout had the world in an uproarabout the possibility of this virus spreading out globally. This outbreakappeared to have started with a patient who had surgery in Kikwit on April 10,1995. Members of the surgical team then developed symptoms similar to those ofa viral hemorrhagic fever disease (Ebola Info. from the CDC 2). From there, thedisease spread to more than 300 others. The most frequent symptoms at the onsetwere fever (94%), diarrhea (80%), and server weakness (74%); other symptomsincluded dysphagia (41%) and hiccups (15%).
Clinical signs of bleeding occurredin 38% of cases (JAMA 274: 373). The World Heath Organization declared onAugust 24, 1995 that the outbreak of Ebola Zaire in Kikwit was officially overafter killing 244 of its 315 known victims (“Ebola Outbreak Officially Over” 1).This outbreak had a rate of death over 75%.Ebola Sudan also occurred in 1976 about the same time as Ebola Zaire.The number of cases was 284 with a death rate of 53% (Le Guenno et al 1271).The outbreak occurred in a hospital setting.
In 1979 a small epidemic wasacknowledged in the same town of Sudan. Of the thirty-four recorded cases therewere twenty-two fatalities (Ebola Info. from the CDC 1). Again the setting forthe small epidemic was a hospital setting with inadequate supplies andunsanitary conditions.
Ebola Reston was isolated in 1989 during an outbreak of cynomolgusmonkeys in a quarantine in Reston, Virginia (Le Guenno et al 1271). Thesemonkeys were imported to the U.S. from the Philippines. This was the onlyoutbreak of the virus to go outside the continent of Africa. This Reston strainof Ebola appears to be highly pathogenic for some monkey species but not forman (Le Guenno et al 1271). No humans fell victim or even contracted the virus.
This also is the only known strain to be able to be transferred through the air.Ebola Tai, which was named after the forest in which it was found, isthe newest stain of the Ebola family. A Swiss female zoologist, who performedan autopsy on a chimpanzee infected with the same virus in the wild, contractedit. This occurred in the Ivory Coast, West Africa in mid November of 1994. Thisis the only know case of Ebola Tai and is the first recorded case that infectionof a human has been linked to naturally infected monkeys anywhere on the Africancontinent. It is also not clear how the chimpanzee may have contracted thedisease.
The usual hosts for these types of hemorrhagic causing viruses arerodents, ticks or mosquitos.The natural reservoir for Ebola viruses has notbeen identified and …
because of the high mortality rate seen in apes they areunlikely to be the reservoir (Le Guenno et al 1271). Thousands of animalscaptured near outbreak areas, are tested for the virus, but efforts have alwaysbeen unsuccessful.The Ebola might never pose a problem to the world community but, thevirus itself is armed with several advantages. It has the ability to mutateinto new strains as we have seen over time.
The fact that there are no knowhosts, which means that there is no way to create a vaccine, coupled with thefact that poor sanitary conditions and lack of medical supplies worsen thespreading of the disease, meaning that there could be a slight chance that thevirus could probably become an international problem.Even if an international crisis were to occur, the virus has to manydownfalls that would over shadow the mass spread of the diseases. First thevirus is easily destroyed by disinfectants (Ebola Info. from the CDC 3). Also,under ultraviolet light the virus falls apart. This ultraviolet light smashestheir genetic material making them unable to replicate.
Ebola’s virulence mayalso serve to limit its speed: its victims die so quickly that they do not havea chance to spread the infection very far. In order for the virus to becomeairborne it would have to mutate in such a way that its outer protective coatingof proteins, the capsid, could resist the forces to which they are subjected inair, like dryness and heat. It would also probably need to change structure toallow infection through the respiratory system. There are no exact measures ofthe rate of Ebola mutation, but the probability of the required mutationshappening is very low (Ornstein, Matthews and Johnson 4).There is no cure or vaccine and it is still unclear if blood fromsurvivors that contain antibodies can be used to synthesize a serum to treat thedisease with.
Some patients have had symptoms subside with the transfusion ofsurvivors blood but not connection to the antibodies and the relief of theillness was proven. There is a good chance that a vaccine may never besynthesized. The kind of research needed to develop a modified live virusvaccine simply could not be done, given the scope of the problem. That is, onlya few people would be working in labs who would need to be vaccinated, and avaccine might want to stockpile in the event of an epidemic. Nevertheless,these are not the scale of circumstances under which the development of avaccine could be afforded (Dr. F.
A. Murphy 3).