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, 2 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 3 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. 4 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, 5 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).
Bibliography
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.