Ebola Hemorrhagic Fever
Edita Buinauskaitė
LSMU MA Infekcinių ligų clinic
Western Africa is a distant land for us, but people are traveling more and more frequently, so it is worth knowing more about the Ebola virus-induced fever, widely discussed in the press and on television. According to the World Health Organization (WHO), the latest outbreak of Ebola virus disease, which began at the end of 2013 and was confirmed by the WHO on April 3, 2014 in Guinea, has already spread to Sierra Leone, Liberia, and Nigeria in Western Africa. This outbreak of Ebola hemorrhagic fever is the largest ever. On August 12, the WHO reported the first confirmed case of Ebola virus infection in Europe: a missionary priest who returned from Liberia died in a hospital in Madrid after being treated for Ebola hemorrhagic fever for 5 days.
Etiology
The Ebola virus, one of the most virulent pathogens for humans, is named after the Ebola River in the Democratic Republic of the Congo, where the first outbreak of the disease was recorded in 1976. This virus belongs to the Filoviridae family, named after the filiform structure of the viruses derived from the word filum (translated from Latin as "thread-like"). The Ebola virus is a single-stranded RNA virus, with a genome structure and replication mechanisms similar to rhabdovirus and paramyxovirus [2, 3]. Clinically, the Ebola virus can be classified as a virus causing hemorrhagic fever, which clinically manifests as coagulation disorders, increased capillary permeability syndrome, and shock [4, 5]. Genetically, the Ebola virus is classified into 5 strains (Zaire, Sudan, Côte d'Ivoire, Bundibugyo, and Reston), which differ in virulence and mortality rates [6]. Since 1976, the Zaire strain has caused many disease outbreaks (from 30 to 300 cases) with a mortality rate of 57–88% [7–12]. The second strain, Sudan virus, resulted in an approximately 50% mortality rate during four known epidemics: two in Sudan in 1970, one in Uganda in 2000, and one in Sudan in 2004 [13–17]. The third strain, Côte d'Ivoire virus, was identified as the pathogen that caused the disease in only one survivor after infection, a scientist studying primate populations [18]. Observing a significant decrease in the great ape population, the scientist conducted an autopsy on a dead chimpanzee found in the forest and thus became infected with the virus. In 2007, the Bundibugyo virus, the fourth strain of the Ebola virus, caused outbreaks of hemorrhagic fever, but the mortality rate (approximately 30%) was lower than that of the most common Zaire and Sudan virus outbreaks. When comparing this strain with other Ebola virus strains, it was found to be most similar to the strain prevalent in Côte d'Ivoire [19]. The fifth strain, Reston virus, differs significantly from the others, as it is most commonly found in animal reservoirs in the Philippines and is not found in Africa [20, 21]. The virus was first discovered in the USA when infected macaques were imported in 1989, leading to fatal outbreaks of hemorrhagic fever. Until 2008, when a swine disease outbreak began in the Philippines, little was known about the Reston virus. Unexpectedly, it was found in studies that some of the pigs were infected with both viruses: the Arteriviridae family's porcine reproductive and respiratory syndrome virus (PRRSV) and the Ebola Reston virus [22].
Epidemiology
The spread of the Ebola virus among wild primates is considered a consequence of contact with an unidentified virus carrier [23–26]. The increase in epidemics in the human population and the frequency of disease outbreaks in recent decades may have been influenced by the consumption of possibly diseased or dead chimpanzees and gorillas as food, leading to a significant decrease in their population.[26, 27]. The Ebola virus circulates in small animal populations, which become a reservoir of infection and a source for both humans and wild primates. Bats have long been included in the list of suspected virus carriers due to several outbreaks of filovirus infections in areas densely populated by them. Bats are included in this list also because they can carry other pathogenic RNA viruses, such as the causative agents of rabies. Laboratory experiments with animals show that filoviruses can cause infection in various ways: alimentary, through the respiratory tract, or simply by direct contact when the skin is compromised [7]. The risk, depending on the nature of the contact, is presented in the table. Humans become infected with the Ebola virus through direct contact with a patient's blood or secretions (e.g., vomit, urine, feces, and possibly sweat). According to epidemiological studies, family members are at risk of infection if they have physical contact with sick relatives, their body fluids, or help prepare the deceased patient for burial [28]. Healthcare workers can become infected with an infection if they care for patients with undiagnosed Ebola hemorrhagic fever without using protective measures. For example, during the 2014 Ebola hemorrhagic fever outbreak, 170 healthcare workers were already infected [8]. Humans and primates can become infected with the virus by ingesting it or getting it into their eyes through virus-contaminated hands [29]. Although epidemiological data show that these pathogens are rarely transmitted from person to person through the respiratory tract, there have been cases where laboratory workers were infected with the virus while using aerosols during medical procedures. Literature provides data that medical procedures can sometimes increase the speed of infection spread. For example, in 1976 in Yambuku, Zaire, in a small missionary hospital where a patient infected with the Ebola virus was treated, medical staff administered antimalarial drugs to all febrile patients. Since all syringes were washed in the same water container and reused, the Ebola virus was transmitted to other patients - infecting another 100 people. They all contracted rapidly progressing Ebola hemorrhagic fever and died [30, 31]. There is no evidence that filoviruses can be transmitted by mosquitoes or other arthropods. If Ebola viruses were to spread in this way, epidemics in central Africa would be much larger and significantly more difficult to control. According to WHO data, the mortality rate from Ebola virus disease can reach up to 52% (according to the data provided by the Center for Infectious Diseases and AIDS (ULAC) on August 28, 2014 - 54%), and from the beginning of the last outbreak until August 28, 2014, there were 3069 suspected and confirmed cases of Ebola in Guinea, Liberia, Sierra Leone, and Nigeria, with 1552 deaths [1].
Since it is difficult to conduct clinical studies during an outbreak of the disease, almost all data on the pathogenesis of Ebola virus-induced hemorrhagic fever have been collected from laboratory experiments conducted with mice, guinea pigs, and small monkeys. It is believed that no matter how the virus enters the human body, the first infected cells are macrophages and dendritic cells [5, 32]. Filoviruses begin to multiply immediately upon entering cells - causing their necrosis and spreading a large amount of new virus particles into the intercellular space. Spreading through regional lymph nodes and creating further replication zones, the virus spreads to dendritic cells, fixes and immobilizes macrophages in the liver, spleen, thyroid, and lymphatic tissue. The rapid systemic spread is due to the virus-induced suppression of type I interferon [33]. As the disease progresses, hepatocytes, adrenal cortex cells, fibroblasts, and many other types of cells become infected, leading to extensive tissue necrosis. In addition to widespread tissue damage, filoviruses cause a systemic inflammatory syndrome. As a result, cytokines, chemokines, and other pro-inflammatory mediators are released from infected macrophages and other cells [32]. Infected with the Ebola Zaire virus Macrophages produce tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta, IL-6, monocyte chemoattractant protein (MCP)-1, and nitric oxide (NO) [34]. These and other mediators were detected in blood samples taken from Ebola virus-infected monkeys and acute Ebola hemorrhagic fever patients in Africa [36, 37]. Products released from necrotic cells stimulate the release of the same mediators and thus exacerbate the infectious response. Clinically, it manifests not as a toxic effect of the virus on the body, but as the body's response to the released mediators, causing fever, general weakness, vasodilation, increased vascular permeability, hypotension, and shock associated with filovirus hemorrhagic fever [38]. Coagulation disorders observed during Ebola hemorrhagic fever are indirectly caused. Macrophages infected with the virus synthesize tissue factor (TF) on the cell surface, acting through the extrinsic coagulation system. Pro-inflammatory cytokines also promote macrophages to produce TF [39]. The activation of these two systems simultaneously helps explain the early onset of the disease, rapid progression, and coagulation disorders in the case of filovirus infections. In blood samples taken from Ebola virus-infected monkeys, D-dimers were found to be produced within 24 hours after viral infection. Elevated D-dimer concentration is also detected in individuals with Ebola hemorrhagic fever [39, 40]. On the second day of the disease in monkeys, the level of C-reactive protein decreases, while the platelet count does not decrease until days 3-4 of the disease, with active platelet adhesion to endothelial cells occurring. As the disease progresses and the liver is affected, there may be insufficient levels of certain plasma coagulation factors. Immune system dysfunction, resulting from impaired dendritic cell function and lymphocyte apoptosis, helps explain the severe course of the disease and often poor outcomes [4]. Filoviruses disrupt the specific immune system response both directly and indirectly. Dendritic cells, responsible for shaping the primary acquired immune response, are the main site of filovirus replication. In vitro studies show that infected cells do not mature and cannot produce antigens for young lymphocytes, hence antibodies against the virus do not form in the blood of patients dying from Ebola hemorrhagic fever [35, 41]. The formation of acquired immunity is also disrupted due to the insufficient number of lymphocytes, contributing to the fatal outcome of Ebola virus infection. Lymphocytes remain uninfected but enter a "watcher" apoptotic state, likely triggered by the released inflammatory mediators and/or the lack of supportive signals from dendritic cells. A similar phenomenon occurs in cases of septic shock [42]. Studying mice infected with lethal Ebola virus infection, the response of M-DC8+ cells and T lymphocytes showed that specific virus-specific lymphocyte proliferation still occurs despite massive surrounding apoptosis. However, this happens too late to prevent death [42].
Clinical Features
The incubation period usually ranges from 2 to 21 days. There is no evidence that asymptomatic individuals in the incubation period can infect another person, but transmission is possible in symptomatic cases. When suspecting symptomatic filovirus infection, appropriate precautions should be taken due to the high concentration of the virus in the patients' blood and other body fluids [43]. Ebola hemorrhagic fever begins with sudden fever, chills, and general malaise. Other symptoms include: weakness, headache, lower back and lumbar pain, nausea, vomiting, watery diarrhea, and abdominal pain. High temperature may be accompanied by bradycardia. Unproductive cough and pharyngitis with a feeling of "lump" in the throat quickly develop. Symptoms last for several days, exhaustion begins and worsens, exhaustion, stupor, and hypotension occur. Although copious bleeding from all body cavities is described in the literature, the disorder of the coagulation system usually manifests as petechiae in the conjunctiva, easily occurring bruises on the body, and impaired clotting at the site of venipuncture. Signs of systemic bleeding are described only in dying patients: blood in the urine and stool is often found, intense bleeding from the gastrointestinal tract is possible. Upon examination of the patient, conjunctival redness and dark red soft palate can be seen [43–45]. A distinctive sign that this may be a filovirus infection is the appearance of a non-pustular maculopapular rash on the upper body during the first week of illness. Formation of antigen-antibody complexes can lead to acute arthralgia and other symptoms. As the disease progresses, kidney failure occurs. There is evidence that infected pregnant women may experience spontaneous abortion. Clinical signs predicting death include decreased intravascular pressure, metabolic disorders, impaired oxygen transport resulting in tachypnea, anuria, delirium, coma, and irreversible shock [47]. Clinical data improve in patients who survive as early as the second week of illness. Recovery from Ebola hemorrhagic fever is long and characterized by weakness, fatigue, and inability to regain weight lost during the illness. The most common phenomenon is the shedding of large areas of skin and hair loss, most likely a consequence of virus-induced necrosis in infected sweat glands and other skin structures [48].
Diagnosis
Early diagnosis of the infection is crucial to initiate supportive treatment, prevent refractory shock, stop the spread of the disease. Leukopenia is detected in the blood, later followed by neutrophilic leukocytosis, lymphopenia, significant thrombocytopenia, impaired platelet aggregation, increased liver enzyme activity. There is a lot of protein in the urine. Studying outbreaks of the disease in Africa, it has been observed that patients with a high concentration of Ebola virus in their blood samples had a higher mortality rate, and for surviving patients, viremia subsided in the second week of illness, presumably due to the lack of virus-specific antibodies [35,46]. Thus, inflammatory cytokines are associated with viremia, bleeding, and fatal disease outcome, while soluble CD40 ligands are associated with survival [49]. There is no data on specific radiological changes caused by viral hemorrhagic fevers. Autopsy studies in monkeys show that filovirus, when entering the respiratory tract, does not cause isolated lung tissue damage visible as focal changes on a chest X-ray [50]. Rapid diagnostic tests for diagnosing Ebola virus infection involve searching for viral antigens in blood or other body fluids using enzyme-linked immunosorbent assay (ELISA) or detecting specific RNA sequences by reverse transcription polymerase chain reaction (PCR) [51]. Data from outbreaks in Africa and experiments with laboratory animals indicate that all individuals infected with filovirus infection, the causative agent of the disease was identified using these methods, but it is not known whether these tests are sensitive enough during the incubation period. The diagnosis of Ebola hemorrhagic fever is confirmed by detecting the replication of the pathogen in cell culture or by electron microscopy identifying particles characteristic of the virus. Since the disease is highly dangerous, all specific tests are performed only in specialized fourth-level biosafety laboratories.
Treatment
There is no confirmed specific method for treating Ebola hemorrhagic fever. Experimental studies with infected primates [3–10] help in the search for effective treatment. Experimental post-exposure prophylaxis is attempted during the incubation period of the disease, the effectiveness of which has been established in laboratory animals. The antiviral drug ribavirin, which inhibits some other RNA viruses, is ineffective in treating this disease [52]. Patients are only given symptomatic supportive treatment [53, 54]. Since the clinical course of filovirus hemorrhagic fever is determined by the host's response to the infection, efforts are made to maintain normal blood circulation function, blood pressure, correct coagulation system disorders, i.e., to preserve the patient's life until the immune system forms a specific immune response to the causative agent. The goal of this immune response is to eliminate the pathogen [53]. A laboratory worker in Russia who worked with the Ebola virus Zaire strain accidentally got infected by a needle stick. He was treated with alpha interferon, immunoglobulin, and other necessary measures, but the worker could not be saved [55]. While there are no confirmed guidelines for post-exposure prophylaxis and treatment, experts should consult on the possibilities of experimental therapy. Many substances intended for post-exposure prophylaxis have been tested in a laboratory with animals infected with the Ebola virus Zaire strain. Excellent results were achieved in experiments with mice receiving alpha interferon before or after exposure to the virus, but treating monkeys with licensed human alpha-2b interferon only delayed the onset of the disease and death for a short time [56]. Treatment with beta interferon is currently under investigation. Polyvalent and monoclonal antibodies against the Ebola virus were effective in mice and guinea pigs, but unfortunately did not stop the progression of the disease in macaques [57]. Rhesus monkeys (or cynomolgus macaques) that were treated with recombinant anticoagulant C protein (rNAPC2) immediately or a day after infection with the Ebola virus had good results in a third of cases, significantly delaying the death of others [58]. rNAPC2 inhibitors, acting through the extrinsic coagulation system, block the interaction of tissue and factor VIIa, weaken the systemic inflammatory response in surviving macaques, and significantly reduce virus replication [59]. Recognizing the similarities between filovirus hemorrhagic fever and septic shock, the possibility of using activated recombinant human C protein (rhAPC) therapy was evaluated. According to preliminary study data, infusion therapy for Ebola virus-infected monkeys yielded positive results [60]. Prospective post-exposure prophylaxis is considered to be an experimental live virus vaccine developed using recombinant vesicular stomatitis virus (VSV) encoding Ebola surface glycoproteins. Effective protection against Ebola Sudan virus infection and partial protection against Ebola Zaire virus infection was achieved with one post-exposure injection administered shortly after mice and monkeys were exposed to the virus: these results indicate that by stimulating a faster specific response to the pathogen, filovirus glycoproteins are presented early to the immune system and neutralize the immunodeficiency caused by viral infection.
Infection Control
The Centers for Disease Control and Prevention and the World Health Organization have issued recommendations for the control of confirmed or suspected filovirus and other highly pathogenic agent infections. More information can be found in these documents: the 2005 Centers for Disease Control and Prevention document "Interim guidance for managing patients with suspected viral hemorrhagic fever in US hospitals" and the 2008 World Health Organization recommendations "Infection prevention and control guidance for care of patients with suspected or confirmed Filovirus haemorrhagic fever in health care settings, with focus on Ebola" [65]. Methods used for surfaces or objects contaminated with filovirus Infection caused by a patient (or suspected patient) body fluids, to neutralize and remove, are similar to those used in hospitals for other bloodborne pathogens. More information on this can be found in the "Temporary Guidelines for Ebola Outbreak Prevention and Management in Healthcare Facilities" released by ULAC on 2014-08-28, prepared according to WHO data (www.ulac.lt/uploads/downloads/Ebola%20 guidelines.pdf).
Role of the Community
With the use of modern technologies, outbreaks of infections are identified and patients are identified much more easily. However, the success of epidemic control largely depends on effective collaboration with the local community in explaining the importance of patient monitoring, sample collection and testing, isolation, and other infection control measures [66, 67]. For this reason, anthropologists and other individuals with specialized knowledge of local cultures are now included in the team responsible for outbreak control [68].