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Am J Physiol Lung Cell Mol Physiol 308: L307–L313, 2015;
Translational Research in Acute Lung Injury and Pulmonary
Ebola: history, treatment, and lessons from a new emerging pathogen
Kevin S. Harrod
Department of Anesthesiology, School of Medicine, University of Alabama-Birmingham, Birmingham, Alabama
Submitted 19 November 2014; accepted in final form 12 December 2014
Address for reprint requests and other correspondence: K. S. Harrod, Dept.
of Anesthesiology, School of Medicine, Univ. of Alabama-Birmingham, BMR
II 324, 901 19th St. S, Birmingham, AL 35294 (e-mail: [email protected]).
The Zaire ebolavirus species is one of five in the Ebolavirus
genus formerly called Ebola hemorrhagic fever viruses. Ebolavirus is classified in the family Filoviridae, in the order
Mononegavirales of single-stranded negative-sense RNA viruses (9). Ebolavirus is made up of five known viral species,
four of which (Zaire ebolavirus, Sudan ebolavirus, Bundibugyo ebolavirus, and Taï Forest ebolavirus) lead to a viral
hemorrhagic fever (VHF) that is highly pathogenic and often
lethal in humans. A fifth ebolavirus, Reston ebolavirus, has
infected humans but has not been shown to cause disease (18).
Other genera of the Filoviridae family are the Marburg marburgvirus, consisting of the two members Marburg (MARV)
and Ravn (RAVV), both causing similar hemorrhagic fevers
with high lethality in humans, and the genus Lloviu cuevavirus
(LLOV), found in bats, with no reported infection in humans
known. The five members of the Ebolavirus genus are the most
highly studied of the Filoviridae, and the natural history of
viral replication of filoviruses is largely known from studies of
the Ebolavirus genus (Fig. 1). Filoviruses are enveloped RNA
viruses that attach to host cells through glycoproteins on the
viral outer membrane that appear to contain a fusion domain as
well, unlike other Mononegavirales, such as respiratory syncytial virus (RSV), that encode a distinct fusion (F) protein.
Following release of the genomic RNA-containing nucleocapsid from the endosome, viral replication takes place by a
RNA-dependent RNA polymerase (L) encoded by the viral
genome. Positive-stranded viral RNA (vRNA) species for each
encoded viral protein (NP, VP35, VP40, GP/sGP, VP30, VP24,
and L) are transcribed initially, followed by production of the
positive-stranded full-length viral antigenomes that serve as the
template for the transcription of negative-stranded viral genomes of progeny virions. Following genomic replication, the
viral genomes are packaged in the nucleocapsid. They traffic to
the cell membrane surface, where the envelope proteins embedded in the cell membrane await and where host envelope
budding around the nucleocapsid takes place, forming nascent
progeny virions that are released. Much of the detailed cell
biology and replication of Ebola virus just described, such as
the switch from viral transcription to viral RNA genomes or the
cell entry mechanisms, are largely unknown in filoviruses but
have been widely studied in a number of other negativestranded RNA viruses such as Paramyxoviridae and pneumoviruses such as the aforementioned RSV. This large body of
literature on similar viruses, while helpful, does not necessarily
indicate that investigations into other less pathogenic viruses
can supplant the study of Ebola virus. As an example, viruses
1040-0605/15 Copyright © 2015 the American Physiological Society
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“DOES IT EVER END?” That was what a neighbor said to me one
evening after hearing of the Guinea Ebola outbreak in West
Africa. We have watched other epidemics unfold before us,
thanks to our around-the-clock media access. The HIV problem developed more quietly owing to the lack of understanding
of human immunodeficiencies, social taboos, and the absence
of the Internet. The full experience of watching epidemics
develop is a more recent phenomenon. The first televised
outbreak was the Severe Acute Respiratory Syndrome (SARS)coronavirus (CoV) epidemic in 2003. This outbreak was
clearly aided by a lack of appreciation for the ability of CoVs
to cause severe disease and the escalation of global travel.
Then the 2009 pandemic H1N1 influenza was predicted and
occurred while an anxious public viewed. Highly pathogenic
avian influenza (HPAI) seems to be on the cusp of efficient
human transmission every year, first with H5N1 serotypes
and now the fearsome H7N9 with its lack of pathogenicity
in its preferred host, birds, thus rendering it difficult to
track. Middle Eastern Respiratory Virus (MERS) CoV has
emerged from its natural host, bats or camels, and is a cause
for concern despite its apparent lack of efficient human-tohuman transmission (40).
Now the emergence of yet another highly pathogenic virus
has taken the biomedical and public imagination in its grasp.
No virus has triggered fear in the general population more than
the filovirus Ebolavirus. This reflects in large part its frightening fatality rates that approach 80% in some outbreak regions.
Currently West Africa is dealing with an outbreak of Zaire
ebolavirus that is causing extraordinary numbers of cases and
deaths (1). The fear in the developed world has led to misguided proposals to lock down borders and halt global traffic.
More familiarity with the natural history of Ebola virus infections, experimental investigations, and knowledge of pathogenesis can help alleviate fears (Table 1). Such knowledge can
also allow us to consider possibilities that have not been widely
discussed beyond a few public health experts and researchers.
This editorial will focus on the aspects of Ebola virus disease
that are closest to the interests of the readership of AJP-Lung,
while providing perspectives and assurances that many of our
family, friends, and neighbors seek from us whether we study
pathogens or not.
Table 1. Ebola overview
䡠 Ebola disease is caused by a filovirus that leads to a viral hemorrhagic
䡠 Transmission among people typically occurs by exposure to body fluids
from infected individuals.
䡠 The incubation period is 3–14 days.
䡠 Human-to-human transmission occurs only after the onset of symptoms.
䡠 Currently, there are no approved vaccines or treatments.
of Paramyxoviridae often inhibit interferon (IFN)-mediated
viral host defense but do so by distinct mechanisms within their
own virus family. For this reason, we cannot rely on our
working knowledge of less pathogenic viruses to fully understand Ebola virus biology.
Ebola outbreaks are largely the result of zoonotic transmission from bats or primates, although the natural reservoir for
Ebola virus is not yet substantiated. Transmission to humans
typically comes from the preparation and consumption of
bushmeat from infected animals. Bats appear to be the most
likely natural reservoir, with several species of fruit bats
implicated despite the lack of apparent disease (31). Nonhuman primates (NHPs) including chimpanzees appear to become infected after eating fruit tainted by the body fluids of
infected fruit bats, although evidence for animal-to-animal
transmission is mostly lacking. Of domesticated animals, pigs
and dogs have been shown to become infected enough to elicit
seroconversion in West Africa despite any apparent disease
(36). The complexity of ecological studies of highly migratory
animals such as fruit bats and the lack of apparent disease in
most animals, primates being the exception, make tracking the
virus difficult and largely rely on seroprevalance studies that
have little informative value other than previous exposure. It
should be noted that bats continue to be prime suspects in the
zoonosis of emerging pathogens, including the CoVs SARSCoV (24), MERS-CoV (23), the highly lethal Nipah (NiV) and
Hendra (HeV) viruses, and the filovirus MARV, not to mention
others. Why bats continue to be central to the transmission of
new viruses into humans, either directly or through an intermediary animal, is of great debate. Clearly a better understanding of bat biology and ecology is warranted to determine
whether bats are opportunistic vectors for many zoonotic
viruses or whether bats are indeed preferred hosts.
The first known outbreak of Ebola occurred in Zaire [what is
now known as the Democratic Republic of the Congo (DRC)]
in 1976 (7). It was attributed to the prototype Ebola strain Zaire
ebolavirus and named for the Ebola River, where the Zaire
index case is thought to have contracted the virus. This outbreak produced the prototype virus upon which much of our
scientific understanding is based. A similar outbreak was
occurring at the same time in the Sudan, but at the time it was
unclear whether the outbreaks were related. A novel virus, first
thought to be the Marburg virus or malaria and then discovered
to be a related yet genetically distinct filovirus, was discovered
by investigators from the Zaire Ministry of Health and the US
Centers for Disease Control and Prevention (CDC). It was later
discovered the viruses in these outbreaks were distinct and
The Current Outbreak in West Africa
March 10, 2014, serves as the start of the chronological
events in the current Ebola outbreak in West Africa, when
public health officials in the villages of Gueckedou and Macenta in southern Guinea alerted the Guinea Ministry of Health
officials and subsequently Medecins sans Frontieres (Doctors
without Borders) regarding a cluster of mysterious diseases in
eight patients in Gueckedou (with three fatalities) and several
cases in Macenta including cases with fatalities of health care
workers (1). Patient samples from 20 cases were analyzed by
RT-PCR for filovirus-specific conserved polymerase L, glycoprotein (GP), and nucleocapsid (NP) genes and were found to
be positive, whereas a panel of other likely etiologic agents
such as Lassa fever and malaria was negative. Retrospective
analysis of cases in Gueckedou indicates that deaths from
Fig. 1. Colorized transmission electron micrograph of the Ebola virus virion.
Created by Cynthia Goldsmith, CDC.
AJP-Lung Cell Mol Physiol • doi:10.1152/ajplung.00354.2014 •
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provide two of the five ebolavirus species, Zaire ebolavirus
and Sudan ebolavirus, known today. High fatality rates were
observed in both outbreaks, with as much as an 88% fatality
rate observed in Zaire. It is these outbreaks that have fostered
much of the fear in the African communities that exists today
(31). Quarantine measures and increased practice of universal
precautions are thought to have contributed to quelling the
outbreak. A second outbreak occurred in 1995 in the DRC, an
outbreak in Uganda in 2000 (caused by the Sudan ebolavirus
species), and a third outbreak in the Congo in 2003. A subsequent outbreak in Uganda in 2007 yielded the Bundibugyo
ebolavirus species after confirmation that a distinct species was
identified by the CDC and the World Health Organization
(WHO) in Bundibugyo district in western Uganda. A second
outbreak caused by the Bundibugyo ebolavirus species was
identified in the Congo in 2012, infecting 57 confirmed cases
with 29 fatalities. Whereas recent Ebola outbreaks may be
news to the public in the West (save for a few cinematic
productions), the frequent recurrence of outbreaks in Africa
has created a much different atmosphere in the villages of
Africans. Fears and taboos run deep in these communities, and
a lack of knowledge regarding the disease and transmission
often necessitates substantial education by aid workers. The
recent outbreaks in Guinea have led to public distrust of
government and international officials, international aid workers, and medical groups providing care in stricken villages and
regions. It should be noted that Western aid workers are often
seen with suspicion by locals, since there is a history of social
imbalance in that, although past epidemics such as the yellow
fever outbreak in the 1920s have led to numerous biomedical
advances, very little benefit has been obtained by the local
communities that suffer the greatest loss (31).
Ebola Hemorrhagic Fever in Humans
Ebola virus infection causes a severe hemorrhagic syndrome
in humans with extraordinary high fatality rates (1). I will use
reports of human disease from the current Guinea outbreak to
highlight this syndrome in humans, because the release of
medical information in this event has been more reliable than
in previous Ebola outbreaks. Ebola disease initially presents
not unlike many other viral infections, i.e., nonspecific in
nature and consisting of fever, malaise, and myalgia. The
initial incubation period following infection can last up to 14
days, a lengthy period considering that most infections show a
typical 2- to 5-day incubation period. It is this lengthy incubation period that can make transmission difficult to halt and
outbreaks difficult to identify, since travel among villages in
indigenous regions is common and lack of a sophisticated
surveillance program or communication among local and regional health care enterprises impedes rapid dissemination of
information. Following the initial symptoms, the most common symptom of a progressing disease is severe gastrointestinal illness with vomiting and diarrhea. The most common signs
and symptoms reported from West Africa in descending order
include fever (87%), fatigue (76%), vomiting (68%), diarrhea
(66%), and loss of appetence (65%). A common sign of Ebola
hemorrhagic fever, and one seen conspicuously in the earlier
outbreaks, is the appearance of bleeding from mucous membranes, conjunctiva, or mouth, and profuse bleeding upon
venipuncture. This sign has been much less dependable as a
sign in patients of the Guinea Ebola outbreak, another reason
why the most recent outbreak may have been slow to identify.
Other internal signs of hemorrhage such as blood in the stools
or bruising are also common to previous outbreaks but less so
in West Africa. Progression of severe disease leads to hypovolemic shock, resultant metabolic disorders, and multiorgan
failure that may result from systemic vascular leak and coagulopathies. Fatality rates in the Guinea Ebola outbreak have
ranged from 70% in Guinea, Sierra Leone, and Liberia to 41%
in Nigeria. Fatality rates in cases of individuals that have
traveled to more developed parts of the globe appear to be
lower, but the death of a patient in Texas highlights that the
fatality rate is not simply a matter of the standard of care in
developing nations vs. those in the United States or Europe
(Table 2).
The Role of the Lung in Ebola Hemorrhagic Fever Illness
VHFs are commonly associated with multiple organ systems
owing to their propensity to infect either immune cells or the
resident cells of the vascular system (38). Ebola VHF is
associated with multiple organ systems, including the lungs,
liver, and renal organs. Little information exists regarding the
molecular pathogenesis of Ebola viruses specifically in the
lung, owing in part to the necessity of care given to the remains
of fatal cases and the fear of transmission from the remains.
For this reason I will limit my discussions here to VHF of
multiple etiologies and lung involvement. Five histological
observations in the lung can be made of VHFs: alveolar
hemorrhage, pulmonary edema, diffuse alveolar damage, interstitial pneumonitis, and, although much less common, bronchopneumonia (39). Although these pathologies can often be
observed in various VHFs, none are diagnostic of or consistent
with any particular etiologic cause of VHF or of VHF in
general. In Ebola VHF, alveolar edema, interstitial pneumonitis, and diffuse alveolar disease can be identified in Ebola
disease. Abundant viral antigen in necrotic debris in the alveolar interstitium and hyaline membranes are characteristic
observations of diffuse alveolar disease. Any of these pathological features can lead to the acute respiratory distress syndrome (ARDS) that occurs at the end of life in fatal Ebola cases
or to the cough that is often reported in severe infections (1).
The detection of viral antigen, indicating active infection of a
particular tissue, most commonly identifies alveolar macrophages and endothelial cells as being harbingers of Ebola in
humans, although widespread infection of any particular cell
type is not atypical. Studies in animal models have provided
more information on the effect of Ebola virus infection in the
Ebola Disease in Animal Models
Multiple animal models of Ebola infection have been utilized to varying degrees under high biocontainment practices
and in regulated facilities (32). The Zaire ebolavirus has been
largely used for most experimental studies, and little is known
about other genera. Mice are generally not permissive of Ebola
infection and are resistant to any disease save for mounting a
serological response with sufficient doses (21). Mouse-adapted
Ebola strains have been developed and show lethality with
similar characteristics of innate immune tropism and characTable 2. Ebola questions and answers
䡠 Is the ebolavirus a new virus that we have only recently discovered?
No, numerous ebolavirus outbreaks have occurred since the discovery of
the virus in 1976, primarily in Africa.
䡠 What are the origins of the virus?
The virus can be found in bats and nonhuman primates, but it is unclear
which is the primary source, or whether another animal is the source.
䡠 How do humans become infected?
It is not always clear, but it appears that the consumption of bushmeat or
fruits and vegetables tainted with the body fluids of infected animals
plays a role.
䡠 How deadly is the ebolavirus?
Fatality rates in Africa are often 50–70% but it is unclear what the fatality
rate would be in a more advanced health care setting.
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Ebola likely extend back to December 2013. Complete sequences of three Ebolavirus isolates indicate a separate Ebolavirus clade distinct from those viruses isolated in the DRC
and Gabon, and this suggests a single introduction from a
presumed animal reservoir sometime in December 2013. As of
this writing, nearly 14,000 cases have been reported in Guinea,
Sierra Leone, and Liberia with nearly 5,000 deaths. The current
status of the outbreak can be found on the CDC website This constitutes the largest Ebola outbreak to date. Molecular clock analysis of isolated genomes
estimates that the outbreak likely progressed undetected in a
number of individuals from the initial index case, thus making
containment by quarantine and standard health practices unable
to limit transmission. Although many lessons can hopefully be
learned from this tragedy, the importance of surveillance and
diagnostics of even small clusters in regions where zoonosis of
deadly pathogens can occur should not be the least of them,
particularly given the ease of nucleic acid-based detection
approaches even in resource-poor health care environments.
asymptomatic yet developed a serological response. The most
recent incident occurred in the Philippines in 2008, when
domesticated pigs were infected (29, 30). Several farmers and
slaughterhouse workers again were asymptomatic yet developed antibodies against the virus. The lack of disease in
humans by Reston virus may offer an opportunity to explore
underlying mechanisms of disease.
The vast majority of information regarding the hematologic
and immunologic pathogenesis in Ebola infection has been
gleaned from the study of infection in NHPs (13). Neutrophilia
and lymphopenia are characteristics of experimental infection
that have been observed in severe human infections. Lymphopenia appears to be the result of extensive lymphocyte
apoptosis in the vasculature and peripheral lymphoid tissues
leading to a sharp drop in CD8⫹ subsets, including natural
killer cells, that precedes the onset of severe disease and may
lead to expansion of the viremia despite a lack of evidence for
ebolavirus tropism for lymphocytes. Some evidence exists for
the role of monocytes, macrophages, and dendritic cells (DCs)
in the release of soluble factors such as nitric oxide and
cytokines such as IFN-␣ that may lead to the activation of
lymphocyte apoptosis. In regard to the coagulopathy that is
common in human Ebola disease, coagulopathies in Ebolainfected NHPs are triggered not by endothelial cytolysis of
Ebola virus but by viremia-induced proinflammatory cytokine
release, including IL-6, that triggers coagulation cascades that
confer fibrinogenic and fibrinolytic events and diffuse intravascular coagulation and hemorrhagic shock (8, 12, 17, 38).
Risk Factors for Transmission
Ebola infections in humans are acquired typically through
direct contact with the body fluids of symptomatic infected
individuals. It is important to reiterate that although the symptoms of early infection may be similar to those of many other
infections, the mucosal hemorrhage, diarrhea, and vomiting
that are characteristic of sustained, severe infections are the
greatest cause for alarm with regard to transmission between
humans. The CDC has established risk factors for determining
the exposure risk for monitoring and movement considerations
often used for travel and public health actions (http://www.cdc.
gov/vhf/ebola/exposure/risk-factors-when-evaluating-personfor-exposure.html). In general, individuals with direct contact
to body fluids of Ebola victims (without appropriate personal protective equipment), direct contact with deceased
Ebola individuals (without appropriate personal protective
equipment), or living in a household with and providing care
to a person with symptomatic Ebola constitute the highest
risk for infection. Having contact with an individual prior to
Ebola symptoms or having arrived from one of the stricken
regions and not shown symptoms for 21 days would classify one
as having no identifiable risk to others. “Low” and “some risk”
categories are also outlined. Many myths and misconceptions
exist with regard to individual risk, and efforts by our national
public health experts, at times, seem to be ignored by our
leadership. Unjustified actions and restrictions on travel
based on fear and not sound medical practice of Ebola risk
can lead to grave impositions, economic disruption, and
disregard for civil liberties.
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teristic disease in the liver leading to coagulopathies and death
(4, 5, 8). Mutations in the mouse-adapted ebolaviruses suggest
that amino acid changes in proteins that antagonize IFNinduced viral host defense are important in the adaptation to
permissive or lethal murine infection (3). Similar findings have
been made using mouse-adapted Ebola virus in guinea pigs and
Syrian hamsters, but the limited reagents available have made
these models less desirable (32).
Clearly, the most utilized animal model of Ebola disease is the
NHP. Rhesus macaques (Macaca mulatta), cynomolgus macaques (Macaca fascicularis), African green monkeys (AGMs)
(Chlorocebus aethiops), and Hamadryas baboons (Papio
hamadryas) have all been used with generally similar results.
The effectiveness of NHPs as a an experimental model should
not be surprising, since monkeys indigenous to West Africa
have been reported to be a common host or intermediary of
zoonotic transmission to humans (11). NHPs infected with
ebolavirus become febrile and exhibit behavior characteristic
of malaise and loss of appetite generally starting about 3 days
following infection (2, 4, 9, 11, 25). Disease progresses to
include anorexia, dehydration from an inability to take fluids,
diarrhea, and rectal bleeding. Some NHP species but not
AGMs developed a petechial rash that has become characteristic of filovirus infections, although the recent Guinea outbreak in humans has not shown this rash to be a common
outcome in severe cases. Viremia occurs generally around the
onset of signs of disease, remains elevated throughout disease,
and can reach viral loads of 106 pfu/ml in the blood (13, 20).
Viral antigen detection occurs predominantly in the liver,
spleen, and lung and to a lesser extent in other tissues. NHPs
typically succumb during days 5–7. It is noteworthy that
typically animal studies do not provide the level of support
given to patients in a critical care setting, particularly with
regard to fluid resuscitation, and these measures are clearly
more difficult at the biosafety level 4 requirement for handling
this pathogen. Thus some aspects of the experimental NHP
model of Ebola do not completely recapitulate that observed in
humans, particularly with the timing of signs of disease. For
instance, the use of needles and sharps for studies of highly
pathogenic organisms like Ebola is strongly curtailed in light of
the seriousness of accidental exposure in this experimental
setting. Nevertheless, the NHP model closely mimics the
disease course and signs of infection in Ebola patients and
provides a good model for the evaluation of vaccines and
An important distinction in the study of Ebola infection in
NHPs is the disparity of responses with different Ebolavirus
genera. Much of the information presented above and subsequently were studied by utilizing Zaire ebolavirus, the most
widely studied Ebola virus. Interestingly, studies in rhesus
macaques with Sudan ebolavirus produced much less disease
and fewer fatalities (4, 9, 11). This is in conflict with five
reported outbreaks of Sudan ebolavirus in Sudan or Uganda
that had case fatality rates of 53% (1976), 65% (1979), 53%
(2000 – 01), 41% (2004), and 41% (2011–13) (6). Another
important distinction is the lack of human infection by Reston
ebolavirus infection in humans (20). Three distinct instances of
Reston ebolavirus infection in NHP colonies have occurred,
including two instances in which infected NHPs were imported
to animal facilities in the US (6). In all cases, NHPs developed
signs of infection whereas humans exposed to the NHPs were
Potential Treatments
Ebola infections are not thought to occur by aerosol transmission, and contact with body fluids, blood, or deceased
individuals has been consistently reported in cases of Ebola
disease. However, two reports suggest that transmission by
aerosol may be possible and should be cautiously expressed to
the public when our health officials seek to alleviate fear of
transmission. Animal-to-animal and animal-to-human transmission is thought to occur when cynomolgus macaques were
imported into a US NHP quarantine facility infected with
Reston virus and became ill (19). Intercage infection of NHPs
was noted in the outbreak, and in some cases the distance
between cages supported the notion of aerosol droplet transmission. Viral antigen detection was heaviest in the lung,
suggesting the respiratory tract as the primary site of infection
and indicating that lung-resident cells, including alveolar epithelial cells, are capable of supporting Reston virus replication.
Seroconversion of workers both in the exporting facility in the
Philippines and in the receiving facility in the US suggest
asymptomatic infections (28). No evidence of direct contact
with NHPs or their body fluids could be established in several
cases, and the resultant conclusion was aerosol transmission. In
this scenario, both the ability to produce infectious droplets and
the ability to become infected by droplet transmission would be
required. Infection by aerosol can be experimentally supported
as well. In an experimental setting, rhesus macaques were
infected by mechanical aerosolization of Zaire ebolavirus with
particles of median mass diameter ranging from 0.8 to 1.2 ␮m
and flow rate of 16.6 l/min in a head-only exposure apparatus
(21). Exposure doses of as little as 400 pfu were able to cause
disease. Interstitial pneumonia centered around terminal bronchioles suggested distal lung exposure. Type I pneumocytes
were observed to have inclusion bodies, indicting a permissive
infection in alveolar epithelial cells. Fatal infections were a
common outcome. Studies to determine whether exhaled infectious particles could be detected were not performed.
Collectively, these findings suggest that aerosol transmission
is possible. A number of thoughts, though, should be considered. First, the ability to eliminate either aerosol or direct
contact as a means of transmission of many pathogens and not
just Ebola in humans is continually debated in public health
and few examples exist where either can be fully excluded.
Unfortunately, this is true of Ebola disease as well. Health care
workers are likely exposed to both. Evidence of Ebola in the
lung has been reported in both natural human infections and
experimental infections by multiple, nonpulmonary routes of
inoculation, although the viral load measured by antigen detection and the lung pathology was reported to be stronger in
the experimental aerosol transmission study (21). It should be
noted that any upper respiratory tract deposition would likely
result in capture by the mucociliary clearance mechanisms and
deposited in gastrointestinal tract, leading to a natural form of
infection, since the consumption of bushmeat is thought to be
the cause of zoonotic transmission of index cases in human
outbreaks (31). The findings from the Reston virus outbreak in
the NHP facility suggest that both release of infectious exhaled
particles and the permissiveness of the respiratory tract are
plausible. Clearly more investigation is needed.
Currently, no vaccines or treatments are licensed by the
Food and Drug Administration for Ebola prophylaxis or intervention within the US, or by any similar global authorities. The
recent widespread emergence of Ebola, the need for extraordinary biocontainment requirements, and the lack of good
small animal models for evaluation all likely contribute to the
dearth of interventions or preventions of disease. A few reports
exist showing efficacy, primarily in NHP models of disease.
IFN-␤ therapy has been shown to increase survival and time to
death in a lethal NHP model, consistent with many other viral
infection models in light of the central role of IFN-mediated
mechanisms in viral host defense (35). Pegylated IFN has not
been studied; however, it has shown to be successful in other
viral infections such as SARS-CoV and hepatitis C virus
infections (16, 26). Another approach has been the use of
coagulation inhibitors to address the coagulopathy associated
with Ebola VHF. Recombinant activated protein C (Xigris; Eli
Lilly), approved and then removed from the market for the
treatment of severe sepsis, has shown some efficacy and
highlights the similarities that exist between VHFs and bacterial sepsis (17). Furthermore, anticoagulation protein c2 derived from nematodes that inhibits Factor VIIa/tissue factor in
the coagulation cascade was able to increase survival and mean
time to death and to reduce intravascular thromboemboli in
Ebola-infected rhesus macaques (12). Despite some success of
anticoagulation end points, the overall survival experimentally
was minimal. The lack of efficacy was likely due to the
inability to directly mitigate the virus. Treatment of the cardiovascular component of the disease alone may be insufficient
as a therapeutic approach.
RNA interference has been investigated as well, and two
approaches using small interfering RNAs (siRNA) are currently in clinical trials (, keyword:
ebola). TKM-Ebola developed by Tekmira Pharmaceuticals is
a formulation of pooled siRNAs targeting the viral RNA
polymerase L, VP24, and VP35 proteins. When delivered at
the time of exposure and on subsequent days, it increased
survival and reduced plasma viral loads (14). Another siRNA
compound utilizing a different formulation, called AVI-6002
and developed by Sarepta Therapeutics (formerly AVI BioPharma),
targets the viral VP24 protein alone with two distinct siRNA
species based on morpholino oligomer design and likewise
increases survival in a lethal NHP model (18). Neither compound has yet been tested in humans.
A novel antiviral called brincidofovir (called CMX001 and
developed by Chimerix), a prodrug formulation of cidofovir
(Vistide, Gilead Sciences), has been proposed for use against
Ebola infection and is currently under Phase I investigation in
humans. Cidofovir has been shown effective against a number
of DNA viruses (particularly cytomegalovirus) as a DNA
polymerase inhibitor (27). The mechanism of action of brincidofovir or cidofovir against RNA viruses is only presumptively thought to be similar. In vitro studies have shown
cidofovir to have antiviral activity against Ebola infection (as
reported by the company in news releases); however, no
studies in experimental in vivo models have been performed. It
should be noted that brincidofovir was used under a compassionate use agreement for the treatment of two cases of Ebola
in the US, with one case surviving while the other did not. One
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Airborne Transmission
and ultimately protection in adulthood to varicella (chickenpox). Convalescent serum has been used in the US in cases in
which blood typing matches between surviving and infected
patients. Although emergency use of such measures may make
sense in outbreak scenarios, concerns exist with rampant use of
blood transfusions in settings with poor hygienic controls, and
the monetizing of convalescent serum in settings where resources are poor is plausible. Hemochromatosis, alloimmunization, and transfusion shock are not uncommon adverse outcomes in sickle cell disease therapy by blood transfusion.
The Guinea ebolavirus epidemic is yet another outbreak with
which we are becoming all too familiar. The high lethality of
Ebola disease coupled with the ease of transmission during
severe infection has created an anxious tension among the
populace that has spread to the public health sector. Just the
ease with which the Ebola has been transmitted in the US
health care settings with so few cases presenting has created a
very heightened sense of unease. The current Ebola epidemic
has exposed numerous fissures between practice and policy in
our health care settings that remind us that new pathogens
bring new challenges to the ongoing struggle of coordinating
the policy makers and practitioners, just as HIV has challenged
us for nearly 30 years now. Furthermore, it has exposed a
serious quandary in our research infrastructure: fewer resources are being funded for research of highly dangerous
pathogens, but yet the need grows more urgent to quickly
develop therapies and vaccines to these emerging pathogens.
At the beginning of this article, I asked you to consider the
question posed by my neighbor, in passing, “Does it ever end?”
The answer: Probably not. Zoonotic outbreaks and the emergence of new pathogens have occurred throughout time and
will continue as nature evolves new microbes to explore novel
niches. We now get to watch them unfold in front of us by a
media apparatus that covets our attention.
This work was supported by National Institute of Allergy and Infectious
Diseases Grant 1R01AI111475-01.
No conflicts of interest, financial or otherwise, are declared by the author(s).
K.S.H. prepared figures, drafted manuscript, edited and revised manuscript,
approved final version of manuscript.
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The treatment that has received the most attention has been
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