History
of Ebola Virus Disease
Emergence
of Ebola in Humans
Ebola
virus disease (EVD), one of the deadliest viral diseases, was discovered in
1976 when two consecutive outbreaks of fatal hemorrhagic fever occurred in
different parts of Central Africa. The first outbreak occurred in the
Democratic Republic of Congo (formerly Zaire) in a village near the Ebola
River, which gave the virus its name. The second outbreak occurred in what is
now South Sudan, approximately 500 miles (850 km) away
Initially,
public health officials assumed these outbreaks were a single event associated
with an infected person who traveled between the two locations. However,
scientists later discovered that the two outbreaks were caused by two
genetically distinct viruses: Zaire ebolavirus and Sudan ebolavirus.
After this discovery, scientists concluded that the virus came from two
different sources and spread independently to people in each of the affected
areas
Viral
and epidemiologic data suggest that Ebola virus existed long before these
recorded outbreaks occurred. Factors like population growth, encroachment
into forested areas, and direct interaction with wildlife (such as bushmeat
consumption) may have contributed to the spread of the Ebola virus
Identifying
a Host
Following
the discovery of the virus, scientists studied thousands of animals, insects,
and plants in search of its source (called reservoir among virologists, people
who study viruses). Gorillas, chimpanzees, and other mammals may be implicated
when the first cases of an EVD outbreak in people occur. However, they – like
people – are “dead-end” hosts, meaning the organism dies following the
infection and does not survive and spread the virus to other animals. Like
other viruses of its kind, it is possible that the reservoir host animal of
Ebola virus does not experience acute illness despite the virus being present
in its organs, tissues, and blood. Thus, the virus is likely maintained in the
environment by spreading from host to host or through intermediate hosts or
vectors
African
fruit bats are likely involved in the spread of Ebola virus and may even be the
source animal (reservoir host). Scientists continue to search for conclusive
evidence of the bat’s role in transmission of Ebola
History
of Ebola Outbreaks
Since
its discovery in 1976, the majority of cases and outbreaks of Ebola
Virus Disease have occurred in Africa. The 2014-2016 Ebola outbreak in West
Africa began in a rural setting of southeastern Guinea, spread to urban areas
and across borders within weeks, and became a global epidemic within months.
Understanding
Pathways of Transmission
The
use of contaminated needles and syringes during the earliest outbreaks enabled
transmission and amplification of Ebola virus. During the first outbreak in
Zaire (now Democratic Republic of Congo – DRC), nurses in the Yambuku mission
hospital reportedly used five syringes for 300 to 600 patients a day. Close
contact with infected blood, reuse of contaminated needles, and improper nursing
techniques were the source for much of the human-to-human transmission during
early Ebola outbreaks.2
In
1989, Reston ebolavirus was discovered in research monkeys imported from
the Philippines into the U.S. Later, scientists confirmed that the virus spread
throughout the monkey population through droplets in the air (aerosolized
transmission) in the facility. However, such airborne transmission is not
proven to be a significant factor in human outbreaks of Ebola. The
discovery of the Reston virus in these monkeys from the Philippines revealed
that Ebola was no longer confined to African settings, but was present in Asia
as well.
By the
1994 Cote d’Ivoire outbreak, scientists and public health officials had a
better understanding of how Ebola virus spreads and progress was made to reduce
transmission through the use of face masks, gloves and gowns for healthcare
personnel. In addition, the use of disposable equipment, such as needles, was
introduced.
During
the 1995 Kikwit, Zaire (now DRC) outbreak, the international public health
community played a strong role, as it was now widely agreed that containment
and control of Ebola virus were paramount in ending outbreaks. The local
community was educated on how the disease spreads; the hospital was properly
staffed and stocked with necessary equipment; and healthcare personnel was
trained on disease reporting, patient case identification, and methods for
reducing transmission in the healthcare setting
In the
2014-2015 Ebola outbreak in West Africa, healthcare workers represented only
3.9% of all confirmed and probable cases of EVD in Sierra Leone, Liberia, and
Guinea combined.5
In comparison, healthcare workers accounted for 25% of all infections during
the 1995 outbreak in Kikwit.6 During the 2014-2015 West Africa outbreak,
the majority of transmission events were between family members (74%). Direct
contact with the bodies of those who died from EVD proved to be one of the most
dangerous – and effective – methods of transmission. Changes in behaviors
related to mourning and burial, along with the adoption of safe burial
practices, were critical in controlling that epidemic
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