The Ebola Virus Essay, Research Paper
Ebola Hemorrhagic Fever
In the world today, there are many known deadly viruses, but few present as great a threat as Ebola, the virus that causes Ebola Hemorrhagic Fever. Key factors in understanding Ebola HF include: Its history, plan of attack, and the diagnosis and treatment of the disease.
The Ebola virus can, and usually does cause a disease called Ebola hemorrhagic fever, which is a Viral hemorrhagic fever. According to the proceedings of the 4th National Symposium on Biosafety, the clinical definition for Viral hemorrhagic fever is as follows. “Viral hemorrhagic fever is an acute infection that begins with fever, myalgia, malaise and progresses to prostration. It shows evidence of vascular dysregulation and increased vascular permeability and can include multisystem involvement. The hemorrhage indicates extent of small vessel involvement but not necessarily large in volume. Shock, encephalopathy, extensive hemorrhage, and poor prognosis should be expected” (4th National 2). The Ebola virus is named after a river in the Democratic Republic of the Congo (formerly Zaire) in Africa, where it was first recognized. The Ebola virus is closely related to the Marburg virus. Both are members of a relatively new family of viruses called Filoviradae. Ebola hemorrhagic fever is classified as a BSL-4 (biosafety level 4) agent, which is the most dangerous in the Centers for Disease Control and Prevention (CDC) classification system. BSL-4 agents are exotic agents that pose a high risk of life-threatening disease, and for which there is no vaccine or therapy. “Ebola hemorrhagic fever is a severe, often-fatal disease in humans and non human primates (monkeys and chimpanzees) that has appeared sporadically since its initial recognition in 1976″ (CDC 1).
Common human perceptions of this virus are, for the most part, accurate in that it is a highly contagious agent that can cause a fatal disease called Ebola hemorrhagic fever. Although, there are a few misconceptions such as the belief that the virus can be transmitted from person to person through the air, which is not known to be true, and later explained. Also, contrary to popular assumptions, humans are not carriers of the virus, as we are with the influenza virus,
for example. The initial patient in an outbreak must have somehow contracted the virus from an infected primate carrier, such as a monkey, which will also be explained.
Listed, are some of the more pertinent outbreaks of Ebola hemorrhagic fever. In 1976, the first and largest outbreak of the virus occurred in Yambuku, Zaire, killing 88% of 318 infected patients. This species was named respectively, Ebola-Zaire, and has appeared in four other outbreaks to date. The Ebola-Sudan species appeared, naturally in the cities of Nzara and Maridi, Sudan also in 1976. The death toll was much less than the Zaire outbreak at 53% of 284 infected persons. In 1995, the Ebola-Zaire species struck again, killing 81% of 315 reported cases. This time, the outbreak occurred in Kikwit, Democratic Republic of the Congo, which was the new name Zaire.
In the United States, to date, no case of the disease in humans has ever been reported, not to say the virus has never been here. In 1989, 1990, and 1996, Ebola, or at least a weaker species of the virus was brought into quarantined facilities in Virginia, Texas, and Pennsylvania by infected monkeys imported from the Philippines. In both 1989 and 1990, four humans were infected with the virus, but did not become ill. Obviously, the species of the virus, now called Ebola-Reston, that entered the United States was a much weaker species than those in Zaire and Sudan. “The Reston outbreak served as an important wake-up call for the U.S. Army and CDC research groups. Among other things, it demonstrated the need for better diagnostic tools” (4th National 10).
Transmission of the Ebola virus is highly dependent upon the initial infection of a human. It is hypothesized that the first infected human in an outbreak must have been infected by an animal. This first infected patient in an outbreak is called the index case. At this point, humans can transmit the virus from person to person in several ways. People can contract the Ebola virus through contact with the blood and/or secretions of an infected person. For this reason, this virus is commonly spread among family members in the course of feeding, holding, or otherwise caring for infected persons in any way that they would come in contact with such
secretions. Also, people can be exposed to the virus through contact with objects, such as needles, that have been contaminated with infected secretions.
The most common means of transmission of the Ebola virus is the spreading of the virus throughout a health-care setting, such as a clinic or hospital, this situation is known as amplification. In African hospitals, for example, where funds and supplies are scarce, patients are often cared for without the use of necessary protective equipment, such as masks, gowns, and gloves. Many cases of exposure to the virus has occurred when health care workers have treated infected persons without using this essential clothing. In addition, many of the needles used for injections to the ill were not of the disposable type. When health care workers used the needles in multiple vials and on multiple patients, they may not have been sterilized, but merely rinsed before reinsertion. If needles or syringes become contaminated with the virus and are then reused, numbers of people can become infected.
The Ebola-Reston Virus species , that appeared in a primate research facility in Virginia, may have been transmitted from monkey to monkey through the air in the facility (CDC 2). The Ebola virus has displayed the ability to be spread through airborne particles (aerosols) under research conditions, but this type of transmission has not been documented among humans in a real-world setting, such as a household or hospital.
“The Ebola virus appears to have an incubation period of four to sixteen days, after which time the impact is devastating” (Carson 1). “One of the few things known about Ebola was that during the initial stages of infection, the virus floods the bloodstream with a glycoprotein–a protein with sugars attached” (Glausiusz 1). This stage apparently occurs during the incubation period. Researchers have recently learned that the glycoprotein is part of a two-pronged attack that leaves the victim bleeding and defenseless. There are actually two forms of the glycoprotein. The first, is released into the bloodstream, and the second, a much larger version, stays attached to the virus. The free form has been found to attach itself to a type of white blood cell called a neutrophil. The neutrophils are the immune system’s front line troops.
They attack and destroy invading viruses and signal the other fighters for the immune system, such as the B cells that make antibodies, and the T cells that kill virus-infected cells. Experts suspect that by binding to the neutrophils, the glycoprotein cripples them so they cannot attack or signal other cells. This process opens the gateway for Ebola to attack the human body.
The virus now begins its assault on the body. It attacks the body’s blood vessels, using the attached, larger glycoprotein as a key to enter endothelial cells, the cells that line the interiors of our veins and arteries. Ebola invades and sabotages the cells’ genetic machinery in order to reproduce itself, it also damages endothelial cells, making blood vessels leaky and weak. The patient first bleeds and then goes into shock as falling blood pressure leaves the circulatory system unable to pump blood to vital organs. Long before the immune system can build up enough antibodies to retaliate, a process that can take weeks, most Ebola HF victims bleed to death.
The signs and symptoms of Ebola hemorrhagic fever are not the same for all patients, but some of the more common early and late symptoms are listed. Within a few days after the end of the incubation period, most Ebola patients experience: high fever, headache, muscle aches, stomach pain, fatigue and diarrhea. Some early Ebola patients have: sore throat, hiccups, rash, red and itchy eyes, bloody vomiting, and bloody diarrhea.
Within one week after the end of the virus’s incubation period, most patients encounter: chest pain, shock and finally death. Also, some late Ebola patients experience complete blindness, internal hemorrhaging, hemorrhaging through the skin, and bleeding from the ears, nose and mouth.
Diagnosing Ebola hemorrhagic fever in a person who has been infected only a few days is difficult because early symptoms, such as red and itchy eyes, and a skin rash, are nonspecific to the virus and are seen in other patients with diseases that occur much more frequently. If a patient has a combination of the symptoms described above, and Ebola virus is suspected, several laboratory test should be performed promptly. These include a blood film examination,
a blood culture, and if the patient has bloody diarrhea, a stool culture should also be performed.
Some of the more common and accurate diagnostic tools for the detection of the Ebola virus are the ELISA (enzyme-linked-immunosorbent serologic assay), PCR (polymerase chain reaction, and a virus isolation procedure can be used to diagnose a case of Ebola hemorrhagic fever within a few days of the onset of symptoms.
Currently, there is no standard treatment for Ebola hemorrhagic fever, although most patiens receive supportive therapy. This consists of balancing the patient’s fluids and electrolytes, maintaining their oxygen levels and blood pressure, and treating them for any complicating infections. It is now known that “The viruses [Ebola and Marburg] can be inactivated by heating at 60?C for 1 hour, by acid treatment at pH 4 or lower, and by organic solvents such as ether” (Johnson 1).
“Scientists and researchers are faced with the challenges of developing additional diagnostic tools to assist in early diagnosis of the disease and ecological investigations of Ebola virus and the disease it causes. In addition, one of the research goals is to monitor suspected areas in order to determine the incidence of the disease. More extensive knowledge of the nature of the virus’ reservoir and how it is spread must be acquired to prevent future outbreaks effectively” (CDC 3). “Filoviruses continue to provide a difficult area for virologists to develop strategies to protect the public and can be seen as the prototype of emerging viruses. We do not understand their natural maintenance strategy and thus cannot predict their emergence nor the factors that might reasonably be expected to increase the risk of their presenting problems to the world. Given our profound ignorance of these viruses, the limited number of episodes we have studied, and their lethal potential, it seems a safe bet that we have additional unpleasant surprises in store. The task now is to gamer [sic] continuing support to understand these elusive agents now that the epidemic has been controlled and public interest has faded” (Peters 3).
Biosafety and Emerging Infections: Key Issues in the Prevention and Control of Viral Hemorrhagic Fevers. Proc. of the 4th National Symposium on Biosafety. Atlanta: Centers for Disease Control and Prevention, 1997.
Carson, Cully C., and Tracy Irons-Georges “Ebola Virus.” Magill’s Medical Guide. 1 (1998): 511-512.
Centers for Disease Control and Prevention. “Ebola Hemorrhagic Fever.” Disease
Information:Viral Hemorrhagic Fevers: Fact Sheets. Atlanta: CDC, 1999.
Glausiusz, Josie. “Ebola’s Lethal Secrets.” Discover Jul. 1998: 24.
Johnson, Karl M. “Filoviradae: Ebola and Marburg Viruses.” Principles and Practice of
Infectious Diseases (1989): 1303-1305.
Peters, C.J. “Emerging Infections: Ebola and other Filoviruses (Emerging and Reemerging
Global Microbial Threats).” The Western Journal of Medicine 164 (1996): 36-39.
Комментариев на модерации: 2.