A virus is an ultramicroscopic infectious organism that, having no independent metabolic activity, can replicate only within a cell of another host organism. A virus consists of a core of nucleic acid, either RNA or DNA, surrounded by a coating of antigenic protein and sometimes a lipid layer surrounds it as well. The virus provides the genetic code for replication, and the host cell provides the necessary energy and raw materials. There are more than 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 and Marburg virus are the two known members of the Filovirus family” (Journal of the American Medical Association 273: 1748). Marburg is a relative of the Ebola virus. 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 was discovered. These filoviruses cause hemorrhagic fever, which is actually what kill victims of the Ebola virus. Hemorrhagic fever as defined in Mosby’s Medical, Nursing, and Allied Health Dictionary as, a group of viral aerosol infections, characterized by fever, chills, headache, malaise, and respiratory or GI symptoms, followed by capillary hemorrhages, and, in severe infection, oliguria, kidney failure, hypotension, and, possibly, death. The incubation period for Ebola Hemorrhagic Fever ranges from 2-21 days (JAMA 273: 1748). The blood fails to clot and patients may bleed from injections sites and into the gastrointestinal tract, skin and internal organs (Ebola Info. from the CDC 2). The Ebola virus has a tropism for liver cells and macrophages, macrophages are cells that engulf bacteria and help the body defend against disease. Massive destruction of the liver is a hallmark feature of Ebola virus infection. This virus does in ten days what it takes AIDS ten years to do. It also requires biosaftey level four containment, the highest and most dangerous level. HIV the virus that causes AIDS requires only a biosaftey level of two. In reported outbreaks, 50%-90% of cases have been fatal (JAMA 273: 1748).
Ebola can be spread in a number of ways, and replication of the virus occurs at an alarming rate. Ebola replication in infected cells takes about eight hours. Hundreds to thousands of new virus particles are then released during periods of a few hours to a few days, before the cells die. The several cycles of replication occur in a primate before the onset of the fever and other clinical manifestations (Ornstein, Matthews and Johnson 7). In most outbreaks, transmission from patient to patient within hospitals has been associated within the reuse of unsterile needles and syringes. High rates of transmission in outbreaks have occurred from patients to heath-care workers and to family members who provide nursing care without appropriate precautions to prevent exposure to blood, other body fluids, vomitus, urine and stool. Risk for transmitting the infection appears to be highest during the later stages of illness, which are often characterized by vomiting, diarrhea, shock, and frequently hemorrhaging (JAMA 274: 374). Even a person who has recovered from the symptoms of the illness may have the virus present in the genital secretions for a brief period after. This makes it possible for the virus to be spread by sexual contact. Complete recovery is reached only when no particles of the virus 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 for nonhuman primates it has been a possibility in a few cases.
Ebola Zaire was identified in 1976 in Northern Zaire and was the first documented appearance of the virus. This strain of the virus effects humans and nonhuman primates. Close contact and dirty needles spread the Ebola virus. The center of the epidemic in Zaire involved a missionary hospital where they reused needles and syringes without sterilization. Most of the staff of the hospital got sick and died. This outbreak infected 318 with a death rate of 93% (Le Guenno et al. 1271). Another fatal case was reported one year later in Zaire but nothing major ever became of it. The most recent case recorded was the infamous breakout in Kikwit, Zaire. This breakout had the world in an uproar about the possibility of this virus spreading out globally. This outbreak appeared 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 of a viral hemorrhagic fever disease (Ebola Info. from the CDC 2). From there, the disease spread to more than 300 others. The most frequent symptoms at the onset were fever (94%), diarrhea (80%), and server weakness (74%); other symptoms included dysphagia (41%) and hiccups (15%). Clinical signs of bleeding occurred in 38% of cases (JAMA 274: 373). The World Heath Organization declared on August 24, 1995 that the outbreak of Ebola Zaire in Kikwit was officially over after 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 was acknowledged in the same town of Sudan. Of the thirty-four recorded cases there were twenty-two fatalities (Ebola Info. from the CDC 1). Again the setting for the small epidemic was a hospital setting with inadequate supplies and unsanitary conditions.
Ebola Reston was isolated in 1989 during an outbreak of cynomolgus monkeys in a quarantine in Reston, Virginia (Le Guenno et al 1271). These monkeys were imported to the U.S. from the Philippines. This was the only outbreak of the virus to go outside the continent of Africa. This Reston strain of Ebola appears to be highly pathogenic for some monkey species but not for man (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, is the newest stain of the Ebola family. A Swiss female zoologist, who performed an autopsy on a chimpanzee infected with the same virus in the wild, contracted it. This occurred in the Ivory Coast, West Africa in mid November of 1994. This is the only know case of Ebola Tai and is the first recorded case that infection of a human has been linked to naturally infected monkeys anywhere on the African continent. It is also not clear how the chimpanzee may have contracted the disease.
The usual hosts for these types of hemorrhagic causing viruses are rodents, ticks or mosquitos. The natural reservoir for Ebola viruses has not been identified and … because of the high mortality rate seen in apes they are unlikely to be the reservoir (Le Guenno et al 1271). Thousands of animals captured near outbreak areas, are tested for the virus, but efforts have always been unsuccessful.
The Ebola might never pose a problem to the world community but, the virus itself is armed with several advantages. It has the ability to mutate into new strains as we have seen over time. The fact that there are no know hosts, which means that there is no way to create a vaccine, coupled with the fact that poor sanitary conditions and lack of medical supplies worsen the spreading of the disease, meaning that there could be a slight chance that the virus could probably become an international problem.
Even if an international crisis were to occur, the virus has to many downfalls that would over shadow the mass spread of the diseases. First the virus is easily destroyed by disinfectants (Ebola Info. from the CDC 3). Also, under ultraviolet light the virus falls apart. This ultraviolet light smashes their genetic material making them unable to replicate. Ebola’s virulence may also serve to limit its speed: its victims die so quickly that they do not have a chance to spread the infection very far. In order for the virus to become airborne it would have to mutate in such a way that its outer protective coating of proteins, the capsid, could resist the forces to which they are subjected in air, like dryness and heat. It would also probably need to change structure to allow infection through the respiratory system. There are no exact measures of the rate of Ebola mutation, but the probability of the required mutations happening is very low (Ornstein, Matthews and Johnson 4).
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There is no cure or vaccine and it is still unclear if blood from survivors that contain antibodies can be used to synthesize a serum to treat the disease with. Some patients have had symptoms subside with the transfusion of survivors blood but not connection to the antibodies and the relief of the illness was proven. There is a good chance that a vaccine may never be synthesized. The kind of research needed to develop a modified live virus vaccine simply could not be done, given the scope of the problem. That is, only a few people would be working in labs who would need to be vaccinated, and a vaccine might want to stockpile in the event of an epidemic. Nevertheless, these are not the scale of circumstances under which the development of a vaccine could be afforded (Dr. F.A. Murphy 3).