Disease
Information
Viral Hemorrhagic Fevers: Fact
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 Ebola Hemorrhagic Fever
Ebola-McLean Outbreak at Freddie Mac
On February 11th, 2000 an outbreak of Ebola5 (Ebola-McLean) was discovered at the headquarters of
the Virginia-based mortgage company Freddie Mac. While CDC scientists are still trying to locate
the zero carrier, it is widely believed that a Structured Finance employee with ties to the island
nation of Cuba transported the virus to the United States through a shipment of infected bananas.
There is no word yet on how many of those were infected with Ebola-Mclean, believed to be the
deadliest and quickest strain of the Ebola series of viral hemorrhagic fevers.
 Ebola Hemorrhagic Fever
What is Ebola hemorrhagic fever?
Ebola hemorrhagic fever (Ebola HF) is a severe, often-fatal disease in humans and nonhuman
primates (monkeys and chimpanzees) that has appeared sporadically since its initial
recognition in 1976.
The disease is caused by infection
with Ebola virus, named after a river in the Democratic Republic of the Congo (formerly
Zaire) in Africa, where it was first recognized. The virus is one of two members of a
family of RNA viruses called the Filoviridae. Three of the four subtypes of Ebola virus
identified so far have caused disease in humans: Ebola-Zaire, Ebola-Sudan, and Ebola-Ivory
Coast. The fourth, Ebola-Reston, has caused disease in nonhuman primates, but not in
humans.
Image: Electron
micrograph of Ebola virus.
Where is Ebola virus found in nature?
The exact origin, locations, and
natural habitat (known as the "natural reservoir") of Ebola virus remain
unknown. However, on the basis of available evidence and the nature of similar viruses,
researchers believe that the virus is zoonotic (animal-borne) and is normally maintained
in an animal host that is native to the African continent. A similar host is probably
associated with the Ebola-Reston virus subtype isolated from infected cynomolgous monkeys
that were imported to the United States and Italy from the Philippines. The virus is not
known to be native to other continents, such as North America.
Where do cases of Ebola hemorrhagic fever occur?
Confirmed cases of Ebola HF have been
reported in the Democratic Republic of the Congo, Gabon, Sudan, and the Ivory Coast. An
individual with serologic evidence of infection but showing no apparent illness has been
reported in Liberia, and a laboratory worker in England became ill as a result of an
accidental needle-stick. No case of the disease in humans has ever been reported in the
United States. Ebola-Reston virus caused severe illness and death in monkeys imported to
research facilities in the United States and Italy from the Philippines; during these
outbreaks, several research workers became infected with the virus, but did not become
ill.
Ebola HF typically appears in
sporadic outbreaks, usually spread within a health-care setting (a situation known as
amplification). It is likely that sporadic, isolated cases occur as well, but go
unrecognized. A table showing a chronological list of
known cases and outbreaks is available.
How is Ebola virus spread?
Infection with Ebola virus in humans is incidental -- humans do not
"carry" the virus. Because the natural reservoir of the virus is unknown, the
manner in which the virus first appears in a human at the start of an outbreak has not
been determined. However, researchers have hypothesized that the first patient becomes
infected through contact with an infected animal.
 After the first case-patient in an outbreak setting
(often called the index case) is infected, the virus can be transmitted in several ways.
People can be exposed to Ebola virus from direct contact with the blood and/or secretions
of an infected person. This is why the virus has often been spread through the families
and friends of infected persons: in the course of feeding, holding, or otherwise caring
for them, family members and friends would come into close contact with such secretions.
People can also be exposed to Ebola virus through contact with objects, such as needles,
that have been contaminated with infected secretions.
Image: Treating patients
with Ebola HF during outbreak of the disease in Kikwit, Democratic Republic of the Congo,
in 1995.
Nosocomial transmission frequently has been associated with outbreaks of Ebola HF. Nosocomial spread includes both types of
transmission described above, but the term is used to describe the spread of disease in a
health-care setting such as a clinic or hospital. In African health-care facilities,
patients are often cared for without the use of a mask, gown, or gloves, and exposure to
the virus has occurred when health care workers treated individuals with Ebola HF without
wearing these types of protective clothing. In addition, when needles or syringes are
used, they may not be of the disposable type, or may not have been sterilized, but only
rinsed before re-insertion into multi-use vials of medicine. If needles or syringes become
contaminated with virus and are then reused, numbers of people can become infected.
The Ebola-Reston virus subtype, which was
first recognized in a primate research facility in Virginia, may have been transmitted
from monkey to monkey through the air in the facility. While all Ebola virus subtypes have
displayed the ability to be spread through airborne particles (aerosols) under research
conditions, this type of spread has not been documented among humans in a real-world
setting, such as a hospital or household.
What are the symptoms of Ebola hemorrhagic fever?
The signs and symptoms of Ebola HF are not
the same for all patients. The table below outlines symptoms of the disease, according to
the frequency with which they have been reported in known cases.
| Time Frame |
Symptoms that occur in
most Ebola patients |
Symptoms that occur in
some Ebola patients |
| Within a few days of becoming
infected with the virus: |
high fever, headache, muscle
aches, stomach pain, fatigue, diarrhea |
sore throat, hiccups, rash,
red and itchy eyes, vomiting blood, bloody diarrhea |
| Within one week of becoming
infected with the virus: |
chest pain, shock, and death |
blindness, bleeding |
Researchers do not understand why some
people are able to recover from Ebola HF and others are not. However, it is known that
patients who die usually have not developed a significant immune response to the virus at
the time of death.
How is Ebola hemorrhagic fever
clinically diagnosed?
Diagnosing Ebola HF in an individual 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
person has the constellation of symptoms described in the table above, and infection with
Ebola virus is suspected, several laboratory tests should be done promptly. These include
a blood film examination for malaria and a blood culture. If the suspected patient has
bloody diarrhea, a stool culture should also be performed.
What laboratory tests are used to
diagnose Ebola hemorrhagic fever?
Antigen-capture enzyme-linked immunosorbent assay (ELISA) testing, IgG ELISA, polymerase
chain reaction (PCR), and virus isolation can be used to diagnose a case of Ebola HF
within a few days of the onset of symptoms. Persons tested later in the course of the
disease or after recovery can be tested for IgM and IgG antibodies; the disease can also
be diagnosed retrospectively in deceased patients by using immunohistochemistry testing,
virus isolation, or PCR.
How is Ebola hemorrhagic fever
treated?
There is no standard treatment for Ebola HF. Currently, patients receive supportive
therapy. This consists of balancing the patient’s fluids and electrolytes,
maintaining their oxygen status and blood pressure, and treating them for any complicating
infections. During a large outbreak of Ebola HF in Kikwit, Democratic Republic of the
Congo, in 1995, eight patients were given blood of individuals who had been infected with
Ebola virus but who had recovered. Seven of the eight patient survived. However,
because the study size was small, and because the characteristics of the participants
predisposed them towards recovery, the efficacy of the treatment remains unknown.
How is Ebola hemorrhagic fever
prevented?
The prevention of Ebola HF in Africa presents many challenges. Because the identity and
location of the natural reservoir of Ebola virus are unknown, there are few established
primary prevention measures.
If cases of the disease do appear, current
social and economic conditions favor the spread of an epidemic within health-care
facilities. Therefore, health-care providers must be able to recognize a case of Ebola HF
should one appear. They must also have the capability to perform diagnostic tests and be
ready to employ practical viral hemorrhagic fever isolation
precautions, or barrier nursing techniques. These techniques include the wearing of
protective clothing, such as masks, gloves, gowns, and goggles; the use of
infection-control measures, including complete equipment sterilization; and the isolation
of Ebola HF patients from contact with unprotected persons. The aim of all of these
techniques is to avoid any person’s contact with the blood or secretions of any
patient. If a patient with Ebola HF dies, it is equally important that direct contact with
the body of the deceased patient be prevented.
Image: Ebola HF
prevention poster used in Kikwit outbreak.
In conjunction with the World Health
Organization, CDC has developed practical, hospital-based guidelines, titled Infection Control for Viral Haemorrhagic Fevers In the African
Health Care Setting. The manual describes how health care facilities
can recognize cases of viral hemorrhagic fever, such as Ebola HF, and prevent further
hospital-based disease transmission by using locally available materials and few financial
resources if a case of VHF is diagnosed in the facility. A similarly practical diagnostic
test that uses tiny samples from patients’ skin has been developed to retrospectively
diagnose Ebola HF in suspected case-patients who have died.
What challenges remain for the
control and prevention of Ebola hemorrhagic fever?
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 to determine the incidence of the disease. More extensive
knowledge of the natural reservoir of Ebola virus and how the virus is spread must be
acquired to prevent future outbreaks effectively.
Unsure about some of the terms used above?
Visit our glossary of terms for help.
1999 Special Pathogens
Branch
Division of Viral and Rickettsial Diseases
National Center for Infectious Diseases
Centers for Disease Control and Prevention
U.S. Department of Health and Human Services
 
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Ebola Hemorrhagic Fever
Ebola Hemorrhagic Fever
After the first case-patient in an outbreak setting
(often called the index case) is infected, the virus can be transmitted in several ways.
People can be exposed to Ebola virus from direct contact with the blood and/or secretions
of an infected person. This is why the virus has often been spread through the families
and friends of infected persons: in the course of feeding, holding, or otherwise caring
for them, family members and friends would come into close contact with such secretions.
People can also be exposed to Ebola virus through contact with objects, such as needles,
that have been contaminated with infected secretions.
