Ebola Virus Infection

Practice Essentials

Ebola virus (see the image below) is one of at least 30 known viruses capable of causing viral hemorrhagic fever syndrome. The genus Ebolavirus is currently classified into 5 separate species: Sudan ebolavirus, Zaire ebolavirus, Tai Forest (Ivory Coast) ebolavirus, Reston ebolavirus, and Bundibugyo ebolavirus. The 2014 outbreak of Ebola virus disease in West Africa, involving Zaire ebolavirus, was the largest outbreak of Ebola virus disease in history.

As of April 10, 2019, an active outbreak of Ebola virus disease (EVD) in the Democratic Republic of the Congo has resulted in 1,206 confirmed and probable cases of Ebola virus disease. [1] An experimental vaccine has been credited with limiting the outbreak’s scope. [2]

Signs and symptoms

The following 2 types of exposure history are recognized:

Primary exposure – This typically involves travel to or work in an Ebola-endemic area
Secondary exposure – This refers to human-to-human exposure (eg, medical caregivers, family caregivers, or persons who prepared deceased patients for burial), primate-to-human exposure (eg, animal care workers who provide care for primates), or persons who collect or prepare bush meat for human consumption

Physical findings depend on the stage of disease at the time of presentation. With African-derived Ebolavirus infection, there is an incubation period (typically 3-8 days in primary cases and slightly longer in secondary cases).

Early findings may include the following:

Fever
Pharyngitis
Severe constitutional signs and symptoms
Maculopapular rash (best seen in white patients)
Bilateral conjunctival injection

Later findings may include the following:

Expressionless facies
Bleeding from intravenous (IV) puncture sites and mucous membranes
Myocarditis and pulmonary edema
In terminally ill patients, tachypnea, hypotension, anuria, and coma

Survivors of Ebola virus disease have developed the following late manifestations:

Myalgias
Asymmetric and migratory arthralgias
Headache
Fatigue
Bulimia
Amenorrhea
Hearing loss
Tinnitus
Unilateral orchitis
Suppurative parotitis

See Clinical Presentation for more detail.

Diagnosis

Diagnostic studies that may be helpful include the following:

Basic blood tests – Complete blood count (CBC) with differential, bilirubin, liver enzymes, blood urea nitrogen (BUN), creatinine, pH
Studies for isolating the virus – Tissue culture (only to be performed in one of a few high-containment laboratories throughout the world), reverse-transcription polymerase chain reaction (RT-PCR) assay
Serologic testing – Enzyme-linked immunosorbent assay (ELISA) for antigens or for immunoglobulin M (IgM) and immunoglobulin G (IgG) antibodies
Other studies – Immunochemical testing of postmortem skin, electron microscopy

See Workup for more detail.

Management

General principles of care are as follows:

Supportive therapy with attention to intravascular volume, electrolytes, nutrition, and comfort care is of benefit to the patient.
Such therapy must be administered with strict attention to barrier isolation; all body fluids contain infectious virions and should be handled with great care.
No specific therapy is available that has demonstrated efficacy in the treatment of Ebola hemorrhagic fever.
No commercially available Ebola vaccines are available, although preliminary data concerning an experimental vaccine have shown it to be 97.5% effective in preventing infection among 90,000 individuals in an active Ebola virus outbreak in the Democratic Republic of Congo. [1]

At present, no specific anti-Ebolavirus agents are available. Agents that have been studied for the treatment or prevention of Ebola virus disease include the following:

Ribavirin (possesses no demonstrable anti- Ebolavirus activity in vitro and has failed to protect Ebolavirus -infected primates)
Nucleoside analogue inhibitors of S-adenosylhomocysteine hydrolase (SAH)
Interferon beta
Horse- or goat-derived immune globulins
Human-derived convalescent immune globulin preparations
Recombinant human interferon alfa-2
Recombinant human monoclonal antibody against the envelope glycoprotein (GP) of Ebola virus
DNA vaccines expressing either envelope GP or nucleocapsid protein (NP) genes of Ebola virus
Activated protein C [3]
Recombinant inhibitor of factor VIIa/tissue factor [4]

In those patients who do recover, recovery often requires months, and delays may be expected before full resumption of normal activities. Weight gain and return of strength are slow. Ebola virus continues to be present for many weeks after resolution of the clinical illness.

See Treatment and Medication for more detail.

Background

Ebola virus is one of at least 30 known viruses capable of causing viral hemorrhagic fever syndrome. (See Pathophysiology and Etiology.) Although agents that cause viral hemorrhagic fever syndrome constitute a geographically diverse group of viruses, all of those identified to date are RNA viruses with a lipid envelope, all are considered zoonoses, all damage the microvasculature (resulting in increased vascular permeability), and all are members of 1 of the following 4 families:

Arenaviridae
Bunyaviridae
Flaviviridae
Filoviridae

Although some of the hemorrhagic fever viruses are normally spread by ticks or mosquitoes, all but one (ie, dengue hemorrhagic fever) are capable of being spread by aerosols, and this capability makes these viruses potential bioterrorism agents.

The family Filoviridae resides in the order Mononegavirales and contains the largest genome within the order. This family contains 2 genera: Ebolavirus(containing 5 species) and the antigenically distinct Marburgvirus (containing a single species).

In patients who have Ebola virus infection, exposure to the virus may be either primary (involving presence in an Ebolavirus -endemic area) or secondary (involving human-to-human or primate-to-human transmission). Physical findings depend on the stage of disease at the time of presentation. (See Presentation.)

Studies have demonstrated that patients who die of Ebola viral infection do not develop a humoral immune response. However, in survivors neutralizing antibody can be detected. It is likely that a broad humoral immune response can increase the likelihood of an infected patient surviving Ebola.

Currently, no specific therapy is available that has demonstrated efficacy in the treatment of Ebola hemorrhagic fever, and there are no commercially available Ebola virus vaccines. (See Treatment.) General medical support is critical. Care must be administered with strict attention to barrier isolation. Because the source of Ebola virus is unknown, education and prevention of primary cases is problematic. Education of communities at risk, especially healthcare workers, can greatly reduce the number of secondary person-to-person transmissions.

Pathophysiology and Etiology

Ultrastructure and pathogenesis

The known members of the family Filoviridae are the genera Ebolavirus (Ebola virus) and Marburgvirus (Marburg virus). According the 2012 virus taxonomy of the International Committee on Taxonomy of Viruses, Ebolavirus is classified into the following 5 separate species:

Sudan ebolavirus
Zaire ebolavirus
Tai Forest ebolavirus (formerly and perhaps still more commonly Ivory Coast ebolavirus or Côte d’Ivoire ebolavirus)
Reston ebolavirus
Bundibugyo ebolavirus

Filoviruses such as Ebola virus share a characteristic filamentous form, with a uniform diameter of approximately 80 nm but a highly variable length. Filaments may be straight, but they are often folded on themselves

Ebola virus has a nonsegmented negative-stranded RNA genome containing 7 structural and regulatory genes. The Ebola genome codes for 4 virion structural proteins (VP30, VP35, nucleoprotein, and a polymerase protein [L]) and 3 membrane-associated proteins (VP40, glycoprotein [GP], and VP24). The GP gene is positioned fourth from the 3′ end of the 7 linearly arranged genes.

After infection, human and nonhuman primates experience an early period of rapid viral multiplication that, in lethal cases, is associated with an ineffective immunologic response. Although a full understanding of Ebola virus disease must await further investigations, part of the pathogenesis has been elucidated.

Most filovirus proteins are encoded in single reading frames; the surface GP is encoded in 2 frames (open reading frame [ORF] I and ORF II). The ORF I (amino-terminal) of the gene encodes for a small (50-70 kd), soluble, nonstructural secretory glycoprotein (sGP) that is produced in large quantities early in Ebola virus infection. [5]

The sGP binds to neutrophil CD16b, a neutrophil-specific Fc g receptor III, and inhibits early neutrophil activation. The sGP also may be responsible for the profound lymphopenia that characterizes Ebola infection. Thus, sGP is believed to play pivotal roles in the ability of Ebola to prevent an early and effective host immune response. One hypothesis is that the lack of sGP production by Marburg virus may explain why this agent is less virulent than African-derived Ebola virus.

Leroy et al reported their observations of 24 close contacts of symptomatic patients actively infected with Ebola. [6] Eleven of the 24 contacts developed evidence of asymptomatic infection associated with viral replication. Viral replication was proven by the authors’ ability to amplify positive-stranded Ebola virus RNA from the blood of the asymptomatic contacts.

A detailed study of these infected but asymptomatic individuals revealed that they had an early (4-6 days after infection) and vigorous immunologic response with production of interleukin (IL)–1β, IL-6, and tumor necrosis factor (TNF), resulting in enhanced cell-mediated and humoral-mediated immunity. In patients who eventually died, proinflammatory cytokines were not detected even after 2-3 days of symptomatic infection.

A second, somewhat larger (120-150 kd) GP, transmembrane glycoprotein, is incorporated into the Ebola virion and binds to endothelial cells but not to neutrophils. Ebola virus is known to invade, replicate in, and destroy endothelial cells. Destruction of endothelial surfaces is associated with disseminated intravascular coagulation, and this may contribute to the hemorrhagic manifestations that characterize many, but not all, Ebola infections.

Clinical infection in human and nonhuman primates is associated with rapid and extensive viral replication in all tissues. Viral replication is accompanied by widespread and severe focal necrosis. The most severe necrosis occurs in the liver, and this is associated with the formation of Councilman-like bodies similar to those seen in yellow fever. In fatal infections, the host’s tissues and blood contain large numbers of Ebola virions, and the tissues and body fluids are highly infectious.

The 5 Ebolavirus species were named for the locations where they caused documented human or animal disease. Two African species, Sudan ebolavirusand Zaire ebolavirus, have been responsible for most of the reported deaths. Clinical disease due to African-derived Ebola virus is severe and, with the exception of a patient who survived infection with a third African species, Ivory Coast ebolavirus, is associated with a mortality ranging from 65% (Sudan, 1979) to 89% (Democratic Republic of the Congo [DRC], December 2002 to April 2003).

A fourth Ebolavirus species, Reston ebolavirus, was first isolated in 1989 in monkeys imported from a single Philippine exporter. A virtually identical isolate imported from the same Philippine exporter was detected in 1992 in Siena, Italy. To date, this species has not been documented to cause human disease.

The fifth Ebolavirus species, also of African lineage, is Bundibugyo ebolavirus, which caused an outbreak in Uganda in 2007-2008, with a mortality of 25%. [7]

Between 1994 and 1997, a stable strain of Ebola virus caused 3 successive outbreaks of hemorrhagic fever in Gabon (mortality, 60-74%). [8] Because the Gabon strain shares a greater than 99% homology of the nucleoprotein and GP gene regions with Zaire ebolavirus, it has not been considered a distinct species.

A likely reservoir for filoviruses has been identified. In 1996, members of the National Institute for Virology of South Africa went to Kikwit, DRC, and evaluated the infectivity of Ebola virus for 24 species of plants and 19 species of vertebrates and invertebrates. [9] Insectivorous bats and fruit bats were found to support Ebola virus replication without dying. Furthermore, serum Ebola titers in infected fruit bats reached as high as 106 fluorescent focus-forming units/mL, and feces contained viable Ebola virus.

Mechanisms of dispersion

African-derived filovirus infections are characterized by transmission from an unknown host (possibly bats) to humans or nonhuman primates, presumably via direct contact with body fluids such as saliva or blood or other infected tissues. Evidence in nonhuman primates indicates that Sudan ebolavirus and Zaire ebolavirus may be transmitted by contact with mucous membranes, conjunctiva, pharyngeal and gastrointestinal (GI) surfaces; through small breaks in the skin; and, at least experimentally, by aerosol. [10]

Dogs have been shown to acquire asymptomatic Ebola virus infections, possibly by contact with virus-laden droplets of urine, feces, or blood of unknown hosts.[11] Of epidemiologic significance was the observation that seroprevalence rates in dogs rose in a linear fashion as sampling approached areas of human cases, reaching as high as 31.8%. Thus, an increase in canine seroprevalence may serve as an indicator of increasing Ebola virus circulation in primary vectors within specific geographical areas.

Human infection with African-derived strains has often occurred in caregivers (either family or medical) and in family members who have prepared dead relatives for burial. Late stages of Ebola virus disease are associated with the presence of large numbers of virions in body fluids, tissues, and, especially, skin. Individuals who are exposed to patients infected with Ebola without proper barrier protection are at high risk of becoming infected.

A report from the DRC identified Ebola virus RNA in 100% of oral secretions from patients who had the viral RNA in their serum. Both serum and oral secretions were tested with reverse-transcriptase polymerase chain reaction (RT-PCR) assay. Thus, oral secretions may be capable of transmitting Ebola virus.

Among infection survivors, only males had been shown to transmit the virus, via semen, in which the virus can persist for up to two years. However, a 2018 study found that previously infected women may also harbor a reservoir of dormant virus, which is theorized to have reactivated upon immunosuppression (suspected to result from pregnancy in the study case). [12]

The first recorded outbreak occurred in 1976, in Yambuku, DRC, where 316 patients were infected. In the largest recorded urban outbreak to date (DRC, 1995; 318 cases), admission to a hospital greatly amplified the frequency of transmission. The lack of proper barrier protection and the use and reuse of contaminated medical equipment, especially needles and syringes, resulted in rapid nosocomial spread of infection. Only after adequate barrier protection and alteration in burial rituals were implemented was the outbreak contained.

Unlike Asian-derived Ebola virus (ie, Reston ebolavirus, traced to a Philippine supplier of primates), African-derived species appear to be spread more often by direct contact than via the respiratory route. However, the Reston species has repeatedly been demonstrated to spread among nonhuman primates and possibly from primates to humans via the respiratory route. Fortunately, although the Reston species has been documented to be capable of infecting in humans, it does not appear to be pathogenic to humans.

Epidemiology

Ebola virus is not endemic in the United States, although, during the 2014 Ebola outbreak, several US healthcare personnel were while in Africa and were transported to the United States for treatment, in addition to a traveller from Liberia who became ill and sought treatment while visiting Texas. The patient later died of the infection. One of his treating nurses then presented with a low-grade fever and tested positive for Ebola virus infection. In addition, individuals in several US states who recently travelled to West Africa have developed fever and other symptoms, prompting evaluation for Ebola virus infection at US hospitals. [13]

Before the 2014 outbreak, several human infections with the Reston strain of Ebola had been acquired by animal care workers at primate holding facilities within the United States. Fortunately, the Reston strain has not demonstrated pathogenic effects in humans. Others at potential risk are laboratory workers who work with infected animals or with the virus in tissue culture.

International statistics

On May 8, 2018, a new outbreak of Ebola virus disease (EVD) was declared in the Democratic Republic of the Congo following laboratory confirmation of two cases of EVD. [14] Before confirmation of the outbreak, 21 patients with signs of hemorrhagic fever had recently been reported in the country, 17 of whom died.[15] On June 20, 2018, the World Health Organization (WHO) announced that the outbreak had been largely contained, with the last known infected person having died on June 9, 2018, bringing the total number of reported deaths to 28. [16]

Ebola and Marburg viruses are responsible for well-documented outbreaks of severe human hemorrhagic fever, with resultant case mortalities ranging from 23% for Marburg virus to 89% for Ebola virus in which more than one case occurred (see Tables 1, 2, 3, 4, and 5 below).

The 2014 Ebola virus outbreak was significant and primarily involved 3 African countries—Guinea, Liberia, Sierra Leone. Localized transmission was been reported in Nigeria. As of October 17, 2014, 8993 total suspected or confirmed cases (5002 laboratory-confirmed) had been reported in these countries, resulting in 4492 deaths. Based on genetic analysis, the virus was 97% identical to the Zaire ebolavirus identified in cases in Gabon and the Democratic Republic of the Congo earlier in 2014. [17, 18] As of October 8, 2014, 401 healthcare personnel in West Africa had been infected with Ebola, 232 of whom had died. [13] Travel-associated cases have also been reported in Senegal and Spain. [17]

At least 3 Americans in Africa were infected with Ebola in the 2014 outbreak, one of whom died of the disease. [19]

Table 1. History of Sudan Ebola Virus Outbreaks

Individuals considered at risk for Ebola hemorrhagic fever include persons with a travel history to sub-Saharan Africa, persons who have recently cared for infected patients, and animal workers who have worked with primates infected with African-derived Ebola subtypes. In 2011, Uganda experienced a reemergence of the disease. [22]

Age-related demographics

In the 1995 outbreak in Kikwit, DRC, infection rates were significantly lower in children than in adults. During this outbreak, only 27 (8.6%) of the 315 patients diagnosed with Ebola virus infection were aged 17 years or younger. This apparent sparing of children occurs even though 50% of the population of the DRC is younger than 16 years. Although definitive evidence is lacking, epidemiologic evidence suggests that children are less likely to come into direct contact with ill patients than adults are.

Other viral hemorrhagic syndromes, such as Crimean-Congo hemorrhagic fever and hantavirus infections, also show a predominance of adult patients and a relative sparing of young children.

Sex-related demographics

Ebola virus infection has no sexual predilection, but men and women differ with respect to the manner in which direct exposure occurs.

Men, by the nature of their work exposure in forest and savanna regions, may be at increased risk of acquiring a primary infection from gathering “bush meat” (primate carcasses) for food, as well as an unknown vector or vectors. Evidence from Africa and the Philippines is compatible with bats being a principal vector of Ebola virus.

Because women provide much of the direct care for ill family members and are involved in the preparation of the bodies of the deceased, they may be at increased risk of acquiring Ebola virus infection through their participation in these activities. However, men and women who are medical healthcare providers seem to share a high and equal risk of infection.

Race-related demographics

Because most cases of Ebola virus infection have occurred in sub-Saharan Africa, most patients have been black. However, no evidence exists for a specific racial predilection.

Prognosis

The overall prognosis for patients with Ebola virus infection is poor. However, those who survive for 2 weeks often make a slow recovery.

With the exception of the Reston strain, Ebola virus is associated with very high morbidity and mortality among patients who present with clinical illness, though these vary according to the causative species. The most highly lethal Ebolavirusspecies is Zaire ebolavirus, which has been reported to have a mortality rate as high as 89%. Sudan ebolavirus also has high reported mortality, ranging from 41% to 65%.

History

In patients who have Ebola virus infection, 2 types of exposure history are recognized: primary and secondary.

A history of primary exposure usually involves travel to or work in an Ebola-endemic area, such as the Democratic Republic of Congo (DRC; formerly Zaire), Sudan, Gabon, or Côte d’Ivoire. A history of exposure to tropical African forests is more common in patients with primary exposure to Ebola than is a history of working within cities in the same region.

Because no natural reservoir of Ebola has been identified, the relation between specific exposure to potential arthropod, animal, or plant vectors and disease remains unproven. Bats are now considered a likely candidate species for a natural reservoir.

Secondary exposure refers to human-to-human or primate-to-human exposures. In each major outbreak, medical personnel or family members who cared for patients or those who prepared deceased patients for burial were at very high risk. Also at risk for infection are animal care workers who provide care for primates. This group includes patients who experienced infection with Reston ebolavirus, as evidenced by antibody production, but did not develop Ebola virus disease.

Physical Examination

Physical findings depend on the stage of disease at the time of presentation. Early in the disease, patients may present with fever, pharyngitis, and severe constitutional signs and symptoms. A maculopapular rash, more easily seen on white skin than on dark skin, may be present around day 5 of infection and is most evident on the trunk. Bilateral conjunctival injection is also common.

Late in the disease, patients often develop an expressionless facies. At this point, bleeding from intravenous (IV) puncture sites and mucous membranes is common. It is worth noting that in the 1976 Ebola outbreak, bleeding was seen in most cases, whereas in the 1995 Ebola outbreak, bleeding occurred in only half of the patients. Myocarditis and pulmonary edema also are seen in the later stages of the disease. Terminally ill patients often die tachypneic, hypotensive, anuric, and in a coma.

Clinical course

Human infections with African-derived Ebolavirus species are characterized by an incubation period that is typically 3-8 days in primary cases and slightly longer in secondary cases. However, cases with incubation periods of 19 and 21 days have been observed.

The onset of clinical symptoms is sudden. Severe headache (50%-74%), arthralgias or myalgias (50%-79%), fever with or without chills (95%), anorexia (45%), and asthenia (85%-95%) occur early in the disease.

Gastrointestinal (GI) symptoms, including abdominal pain (65%), nausea and vomiting (68%-73%), and diarrhea (85%), soon follow. Evidence of mucous membrane involvement includes conjunctivitis (45%), odynophagia or dysphagia (57%), and bleeding from multiple sites in the GI tract. Bleeding from mucous membranes and puncture sites is reported in 40%-50% of patients.

A rash, which in survivors desquamates during convalescence, is seen in approximately 15% of patients. Terminally ill patients often are obtunded, anuric, tachypneic, normothermic, and in shock.

Although the mechanism is unclear, hiccups were noted in fatal cases of Ebola virus disease in both the 1976 and the 1995 outbreaks in the DRC. In the 1995 Ebola virus outbreak in Kikwit, DRC, tachypnea was the single most discriminating sign that separated survivors (none of whom had tachypnea) from patients who died (37% of whom had tachypnea).

Complications

Ocular complications were reported in 3 (15%) of 20 survivors of the 1995 Ebola outbreak in the DRC. Patients reported ocular pain, photophobia, increased lacrimation, and decreased visual acuity. All had documented uveitis, and all improved with topical application of 1% atropine and steroids.

Survivors of Ebola virus disease have developed the following late manifestations:

Myalgias
Asymmetric and migratory arthralgias
Headache
Fatigue
Bulimia
Amenorrhea
Hearing loss
Tinnitus
Unilateral orchitis
Suppurative parotitis

Diagnostic Considerations

Ebola hemorrhagic fever should be considered in patients who have recently traveled to areas where Ebola has been reported or in patients who have been exposed to known cases and who exhibit signs and symptoms consistent with Ebola virus infection.

A main concern in dealing with Ebola virus infections is the potential for human-to-human spread of virus before the correct diagnosis is made. This risk includes all medical personnel in direct contact with the patient, the patient’s blood, or other body fluids or tissues. Family members who care for patients or who are involved in burial ceremonies and come into contact with the body, blood, or other body fluids are also at high risk for Ebola virus infection.

In addition to the conditions listed in the differential diagnosis, other problems to be considered include the following:

Acute surgical abdomen (as distinct from abdominal signs of Ebola hemorrhagic fever)
Crimean-Congo hemorrhagic fever
Marburg hemorrhagic fever
Other hemorrhagic fevers

Differential Diagnoses

Malaria
Typhoid Fever

Approach Considerations

The US Food and Drug Administration (FDA) has granted emergency authorization for two new tests for detecting Ebola in humans. The tests, which can detect Ebola in blood or urine samples in 1 hour, can be performed on-site in hospitals with the proper lab equipment from the tests’ manufacturer, BioFire Defense. In other tests, samples must be sent from hospitals to be run in specialized labs and require 24-48 hours to produce results. Emergency use authorizations by the FDA permit the use of unapproved medical products in dealing with life-threatening illnesses when no approved or available alternatives exist. [23]

Laboratory Studies

Basic blood tests

The early phase of infection is characterized by thrombocytopenia, leukopenia, and a pronounced lymphopenia. Neutrophilia develops after several days, as do elevations in aspartate aminotransferase and alanine aminotransferase. Bilirubin may be normal or slightly elevated.

With the onset of anuria, blood urea nitrogen and serum creatinine increase. Terminally ill patients may develop a metabolic acidosis that may contribute to the observation that these patients often have tachypnea, which may be an attempt at compensatory hyperventilation.

Studies for isolating virus

Definitive diagnosis rests on isolation of the virus by means of tissue culture or reverse-transcription polymerase chain reaction (RT-PCR) assay. However, isolation of Ebola virus in tissue culture is a high-risk procedure that can be performed safely only in a few high-containment laboratories throughout the world.

Serologic testing for antibody and antigen

The indirect fluorescence antibody test (IFAT) is associated with false-positive results. Concerns over the sensitivity and utility of this test have resulted in the development of confirmatory serologic tests. In infected patients who survive long enough to develop an immune response, the immunoglobulin M (IgM) and immunoglobulin G (IgG) enzyme-linked immunosorbent assay (ELISA) tests may be useful in the diagnosis of Ebola virus infection. Both ELISA tests have been demonstrated to be sensitive and specific.

IgM-capture ELISA uses Zaire ebolavirus antigens grown in Vero E6 cells to detect IgM antibodies to this strain. Results become positive in experimental primates within 6 days of infection but do not remain positive for extended periods. These qualities indicate that the IgM test may be used to document acute Ebola infection.

IgG-capture ELISA uses detergent-extracted viral antigens to detect IgG anti-Ebola antibodies. It is more specific than the IFAT, and it remains positive for long periods. Accordingly, this test appears to be superior for seroprevalence investigations.

An antigen detection ELISA test is available that identifies Ebola virus antigens.

Other studies

The risks in viral isolation have led to the development of various modalities that better lend themselves to laboratories with limited containment systems. Tests used to confirm the diagnosis of Ebola virus infection include an immunohistochemical test performed on formalin-fixed postmortem skin taken from patients who have died of Ebola hemorrhagic fever. This test is safe, sensitive, and specific, and it can be used for diagnosis and surveillance.

Electron microscopy has been used to identify filoviruses in tissue but has obvious limitations as a diagnostic modality in the areas where human outbreaks have occurred. [24] It is not readily available in areas where Ebola virus is endemic.

Histologic Findings

Although capable of involving many tissues, Ebola virus has a predilection for endothelial cells, hepatocytes, and mononuclear phagocytes. Viral replication is associated with extensive focal necrosis and is most severe in the liver, spleen, lymph nodes, kidney, lung, and gonads.

In the liver, eosinophilic globules derived from focal necrosis of hepatic cells (Councilman-like bodies), similar to those seen in yellow fever, are prevalent. However, the focal necrosis associated with Ebola virus replication results in a minimal effective inflammatory response. Late in the disease, the intestinal mucosa may separate from the lamina propria and slough.

Approach Considerations

General medical support is critical and should include replacement of coagulation factors and heparin if disseminated intravascular coagulation develops. Such care must be administered with strict attention to barrier isolation. All body fluids (blood, saliva, urine, and stool) contain infectious virions and should be handled with great care.

Currently, no specific therapy is available that has demonstrated efficacy in the treatment of Ebola hemorrhagic fever. Surgical intervention generally follows a mistaken diagnosis in which Ebola-associated abdominal signs are mistaken for a surgical abdominal emergency. Such a mistake may be fatal for the patient and for any surgical team members who become contaminated with the patient’s blood.

No commercially available Ebola vaccines are available, although preliminary data concerning an experimental vaccine have shown it to be 97.5% effective in preventing infection among 90,000 individuals in an active Ebola virus outbreak in the Democratic Republic of Congo. [1]

Supportive Care

Supportive therapy with attention to intravascular volume, electrolytes, nutrition, and comfort care is of benefit to the patient. Intravascular volume repletion is one of the most important supportive measures.

Survivors can produce infectious virions for prolonged periods. Therefore, strict barrier isolation in a private room away from traffic patterns must be maintained throughout the illness. Patient’s urine, stool, sputum, and blood, along with any objects that have come in contact with the patient or the patient’s body fluids (such as laboratory equipment), should be disinfected with a 0.5% sodium hypochlorite solution. Patients who have died of Ebola virus disease should be buried promptly and with as little contact as possible.

Pharmacologic Therapy

Nucleoside analogue inhibitors of the cell-encoded enzyme S-adenosylhomocysteine hydrolase (SAH) have been shown to inhibit Zaire Ebolavirus replication in adult BALB/c mice infected with mouse-adapted Ebola virus. [25] Inhibition of SAH indirectly inhibits transmethylation reactions required for viral replication. Treatment response was dose-dependent. When doses of 0.7 mg/kg or more every 8 hours were begun on day 0 or 1 of infection, mortality was completely prevented. Even when the drug was given on day 2, 90% survived.

Smith et al found that in rhesus macaques infected with a lethal dose of Ebola virus, treatment with interferon beta early after exposure led to a significant increase in survival time, though it did not reduce mortality significantly. [26]These findings suggest that early postexposure interferon-beta therapy may be a promising adjunct in the treatment of Ebola virus infection.

Passive immunity has been attempted by using equine-derived hyperimmune globulins and human-derived convalescent immune globulin preparations. In Ebolavirus -infected cynomolgus macaques, use of human recombinant interferon alfa-2b in conjunction with hyperimmune equine immunoglobulin G (IgG) delayed but did not prevent death.

Equine IgG containing high-titer neutralizing antibodies to Ebola virus protected guinea pigs and baboons but was not effective in protecting infected rhesus monkeys.

During the 1995 outbreak in Kikwit, DRC, human convalescent plasma was used to treat 8 patients with proven Ebola disease, and only 1 patient died. Subsequent studies could not demonstrate survival benefit conferred by convalescent plasma products. The survival of these patients suggests that passive immunity may be of benefit in some patients.

Four laboratory workers in Russia who had possible Ebola exposure were treated with a combination of a goat-derived anti-Ebola immunoglobulin plus recombinant human interferon alfa-2. One of these patients had a high-risk exposure and developed clinical evidence of Ebola virus infection. All 4 patients recovered.

A recombinant human monoclonal antibody directed against the envelope glycoprotein (GP) of Ebola virus has been demonstrated to possess neutralizing activity. This Ebola virus−neutralizing antibody may be useful in vaccine development or as a passive prophylactic agent.

DNA vaccines expressing either envelope GP or nucleocapsid protein (NP) genes of Ebola virus have been demonstrated to induce protection in adult mice exposed to the virus. These vaccines were administered by coating gold beads with DNA expressing the genes for either GP or NP, and they were delivered by skin particle bombardment using a PowderJect-XR gene gun. Both vaccines induced measurable antibody responses detected by enzyme-linked immunosorbent assay (ELISA) and induced cytotoxic T-cell immunity.

Other experimental therapies that use available drugs, though not approved by the US Food and Drug Administration (FDA) for treatment of Ebola virus infection, may be considered. Agents that may reduce mortality without directly effecting viral replication include activated protein C [3] and a recombinant nematode anticoagulant protein (NAP) that inhibits activated factor VII-tissue factor complex. [4] NAP resulted in attenuation of the coagulopathy associated with decreased fibrinolysis and fibrin deposition with a resultant decrease in the severity of the systemic inflammatory response syndrome.

In a rhesus macaque model of Ebola hemorrhagic fever, which carries a mortality approaching 100%, Geisbert et al administered recombinant nematode anticoagulant protein, a potent inhibitor of TF-initiated coagulation. [4] One third of the monkeys given the nematode anticoagulant protein survived a lethal dose of Ebola virus, whereas 16 of the 17 (94%) control animals died. This approach targeted the hemorrhagic disease component of the infection rather than the virus itself.

In April 2016, the FDA granted orphan designation to aphidicolin for the treatment of Ebola virus infection. Aphidicolin is an inhibitor of B-family DNA polymerases, which inhibit the cell cycle at the G1/S border. If the cell is exposed to aphidicolin during S-phase, DNA replication is interrupted. [27]

In a benchtop experiment analyzing the influence of cell cycle arrest on Ebola virus infection, cells in G1/S phase were exposed to aphidicolin, a potent cell cycle inhibitor. A dose-dependent decrease in Ebola-infected cells was noted. Cells exposed to aphidicolin were allowed to resume cell cycle and then exposed to Ebola virus, which showed a time-dependent increase in infected cells. [28]

Small interfering RNA

One approach to blocking Ebola virus replication involves the use of antisense nucleotides that are complementary to sequences in the RNA polymerase complex. Shortly after a lethal challenge of Zaire Ebola virus was given, the administration of small interfering RNAs (siRNAs) packaged in stable nucleic acid-lipid particles targeting the RNA polymerase L protein protected guinea pigs [29] and macaques [30] .

More recently, third-generation synthetic antisense oligonucleotides called phosphorodiamidate morpholino oligomers (PMOs) have been shown to sterically hinder mRNA processing. Positively charged Ebola virus–specific PMOs that target VP24 and VP35 mRNA sequences (AVI-6002, a combination of AVI-7537 and AVI-7539) protect rhesus monkeys after lethal viral challenge.[31, 32] In addition, a recently completed phase I study of AVI-6002 in human volunteers showed that the drug was safe and well-tolerated. [33]

Monoclonal antibodies

Postexposure prophylaxis

Preliminary studies in cynomolgus macaques given a cocktail of 3 different murine monoclonal antibodies (mAbs; ZMab) directed against Ebola virus envelope glycoprotein epitopes demonstrated postexposure prophylactic activity 1-2 days after an Ebola virus challenge. [34] That result was matched by a mixture of 3 chimerized anti–Ebola virus mAbs (MB-003) having human constant regions produced in genetically modified tobacco plants. When given as postexposure prophylaxis 2 days after viral challenge, MB-003 was active both in mice and rhesus macaques. [35, 36]

Therapy

The focus of mAb research is now shifting toward treatment of established infection. In that regard, 43% of rhesus macaques treated with MB-003 after onset of Ebola virus infection survived versus none of the untreated controls. [37]Established infection was defined as fever and positive Ebola virus reverse-transcription polymerase chain reaction (RT-PCR) result. Similarly, ZMab yielded a 50% survival rate in cynomolgus macaques when given starting on day 4 after viral challenge. [38]

Recently, an optimized combination of humanized mAbs produced in genetically modified tobacco plants and having specificity for 3 different Ebola virus glycoprotein epitopes rescued 100% of rhesus macaques even when given at advanced stages of disease 5 days after viral challenge (ZMapp; Mapp Biopharmaceutical, Inc., San Diego, CA, USA; and Defyrus, Inc., Toronto, Canada). [39, 40] In addition, two patients with Ebola virus disease in the United States who recently received ZMapp through emergency investigational new drug approval (US FDA) experienced declines in viral load and survived. [41]Subsequently, another 3 of 4 individuals treated with ZMapp survived. [42] These results suggest that ZMapp may prove useful for the treatment of established infection in humans.

Diet and Activity

Nutrition is complicated by the patient’s nausea, vomiting, and diarrhea.

Recovery often requires months, and delays may be expected before full resumption of normal activities. Weight gain and return of strength are slow. Ebola virus continues to be present for many weeks after resolution of the clinical illness. Semen from men recovering from Ebola infection has been shown to contain infectious virus, and Ebola has been transmitted by sexual intercourse involving recovering men and their sex partners. Any individuals who were exposed to infected patients should be watched closely for signs of early Ebola virus disease.

Prevention

Prevention in healthcare personnel

Guidance from the CDC recommends that healthcare personnel who care for patients infected with Ebola virus (ie, physicians, nurses, other clinicians) wear personal protective equipment (PPE) that does not expose any skin. This includes a surgical hood that covers the head and neck and a single-use full face shield (rather than goggles), in addition to either a N95 respirator or powered air-purifying respirator instead of a mask.

The CDC now recommends that clinicians train rigorously at donning and doffing PPE in a stepwise manner and demonstrate competency. A trained monitor should oversee each time a clinician puts on and takes off this gear.

During patient care, the PPE should not be adjusted, and the worker’s gloved hands should be disinfected frequently using an alcohol-based hand rub (ABHR), especially after body fluids are handled. [43]

Vaccination

rVSV-ZEBOV-GP, an experimental recombinant vesicular stomatitis virus (rVSV)–based vaccine candidate expressing the glycoprotein of a Zaire strain of Ebola virus (ZEBOV) has shown, in preliminary data, a 97.5% rate of preventing infection among recipients. The World Health Organization approved use of the rVSV-ZEBOV-GP vaccine during outbreaks as part of an Expanded Access/Compassionate Use protocol. From August 2018 to March 2019, 94,000 individuals, including 29,000 healthcare personnel and front-line responders, received the vaccine. Among recipients, only 71 developed Ebola virus disease, most of whom contracted the infection within 10 days of vaccination, before the vaccine is believed to confer full protection. [2]

Two vaccines have been studied in a randomized, placebo-controlled trial in Liberia—the chimpanzee adenovirus 3 vaccine and the recombinant vesicular stomatitis virus vaccine. Both vaccines elicited a sustained immune response in study participants. [44]

Work continues on a vaccine for Ebola virus infection in primates. Sullivan et al reported on the combination of naked DNA vaccine capable of encoding Ebola proteins followed by a booster vaccination with a recombinant adenoviral vector expressing Ebola GP(Z). [45]

In this study, cynomolgus macaques were injected with 3 doses of the DNA vaccine, 1 dose every 4 weeks. [45] Twelve weeks later, the macaques were vaccinated with the recombinant adenoviral vector. After another 12 weeks, unvaccinated macaques and vaccinated macaques were injected with a lethal dose of Ebola virus. All of the unvaccinated macaques died, whereas none of the vaccinated macaques died.

This work indicates that primates can be vaccinated against Ebola virus and can develop both a cell-mediated response (thought to be a result of the DNA vaccine) and a humoral antibody response (thought to be a result of the recombinant adenoviral vaccine).

Other efforts to design vaccines that work in primates used strategies that were successful in mice and guinea pigs. Geisbert et al studied a series of vaccines containing RNA replicon particles from an attenuated strain of Venezuelan equine encephalitis virus that expressed Ebola virus GP and NP, a recombinant vaccinia virus that expressed Ebola virus GP, liposomes containing lipid A and inactivated Ebola virus, and a concentrated, inactivated whole-virion Ebola preparation. [46]

Although these vaccines protected rodents against an Ebola virus challenge, they did not protect cynomolgus macaques or rhesus macaques against exposure to the virus.

Ebola is transmissible from person to person via direct contact with an infected patient’s blood or other body fluids. Airborne transmission of Reston ebolavirusis known to have occurred among primates; thus, although most cases in humans occur after direct contact with a patient or their blood or body fluids, transmission of Ebola virus via the airborne route cannot be dismissed.

Infection control inside and outside of medical facilities relies on barrier protection using double gloves, fluid-impermeable gowns, face shields with eye protection, and coverings for legs and shoes.

Consultations

Whenever the diagnosis of Ebola or any other viral hemorrhagic fever is considered, the Centers for Disease Control and Prevention (CDC), along with local and state health officials, should be contacted. A consultation with an infectious diseases physician should be promptly obtained, and strict barrier isolation should be instituted.

No attempt should be made to culture the virus, except when culture can be performed in a maximum-containment biosafety level 4 laboratory with laboratory personnel wearing positive-pressure suits equipped with high-efficiency particulate air filters and an umbilical-fed air supply.

Guidelines Summary

CDC Recommendations for Healthcare Personnel and Health Officials

An advisory from the CDC’s Health Alert Network on the evaluation of patients for Ebola by health-care personnel and health officials include the following [47] :

Ebola should be considered as a possibility in patients who present with fever, myalgia, severe headache, abdominal pain, vomiting, diarrhea, or unexplained bleeding or bruising
For any patient presenting with fever or other symptoms consistent with Ebola, inquiries should be made as to whether the patient traveled to an Ebola-affected country in the 21 days before the onset of illness
Patients who report having travelled to an Ebola-affected country and who are exhibiting Ebola symptoms should be isolated in a private room with a private bathroom, and standard, contact, and droplet precautions should be implemented
Local and state health departments should be notified immediately

According to the advisory, individuals at the highest risk for Ebola infection include the following [47] :

Anyone who has had direct contact with the blood and body fluids of an individual diagnosed with Ebola
Anyone who has had close physical contact with an individual diagnosed with Ebola
Anyone who lived with or visited an Ebola-diagnosed patient while the patient was ill

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