Diagnosis

When the diagnosis of EVD is suspected, the travel and work history along with exposure to wildlife are important factors to consider. The diagnosis is confirmed by isolating the virus, detecting its RNA or proteins, or detecting antibodies against the virus in a person's blood. Isolating the virus by cell culture, detecting the viral RNA by polymerase chain reaction (PCR) and detecting proteins by enzyme-linked immunosorbent assay (ELISA) works best early and in those who have died from the disease. Detecting antibodies against the virus works best late in the disease and in those who recover.

During an outbreak, virus isolation is often not feasible. The most common diagnostic methods are therefore real-time PCR and ELISA detection of proteins, which can be performed in field or mobile hospitals. Filovirions can be seen and identified in cell culture by electron microscopy due to their unique filamentous shapes, but electron microscopy cannot tell the difference between the various filoviruses despite there being some length differences.


Laboratory Testing

Changes on laboratory tests as a result of Ebola virus disease include a low platelet count in the blood, an initially decreased white blood cell count followed by an increase in the white blood cell count, elevated levels of the liver enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and abnormalities in clotting often consistent with disseminated intravascular coagulation (DIC) such as a prolonged prothrombin time, partial thromboplastin time, and bleeding time.


Differential diagnosis

Early symptoms of EVD may be similar to those of other diseases common in Africa including malaria and dengue fever.[11] The symptoms are also similar to those of Marburg virus disease and other viral hemorrhagic fevers.


The complete differential diagnosis is long and includes many other infectious diseases such as typhoid fever, shigellosis, rickettsial diseases, cholera, sepsis, borreliosis, EHEC enteritis, leptospirosis, scrub typhus, plague, Q fever, candidiasis, histoplasmosis, trypanosomiasis, visceral leishmaniasis, measles, and viral hepatitis among others. Non-infectious diseases that can be confused with EVD include acute promyelocytic leukemia, hemolytic uremic syndrome, snake envenomation, clotting factor deficiencies/platelet disorders, thrombotic thrombocytopenic purpura, hereditary hemorrhagic telangiectasia, Kawasaki disease, and warfarin poisoning among others.

sources : wikipedia

Pathophysiology

Pathogenesis schematic

Cells lining the inside of blood vessels (endothelial cells), macrophages, monocytes, and liver cells are the main targets of infection. Macrophages are the first cells to be infected with the virus and this infection results in cellular death. Endothelial cells can be infected within three days after exposure to the virus. After infection, a secreted glycoprotein, known as small soluble glycoprotein (sGP) or as the Ebola virus glycoprotein (GP), is synthesized. Ebolavirus replication overwhelms protein synthesis of infected cells and host immune defenses. The GP forms a trimeric complex, which binds the virus to the endothelial cells. The sGP forms a dimeric protein that interferes with the signaling of neutrophils, a type of white blood cell, which allows the virus to evade the immune system by inhibiting early steps of neutrophil activation. These white blood cells also serve as carriers to transport the virus throughout the entire body to places such as the lymph nodes, liver, lungs, and spleen. The presence of viral particles and cell damage resulting from viruses budding out of the cell causes the release of chemical signals (such as TNF-α, IL-6, and IL-8), which are molecular signals for fever and inflammation. The damage to human cells, caused by infection of the endothelial cells, decreases blood vessel integrity. This loss of vascular integrity is furthered with the synthesis of GP, which reduces specific integrins responsible for cell adhesion to the intercellular structure, and damage to the liver, which leads to improper clotting.

Filoviral infection is also known to interfere with proper functioning of the innate immune system. Ebolavirus proteins blunt the human immune system's response to viral infections by interfering with cells' ability to produce and respond to interferon proteins such as interferon-alpha, interferon-beta, and interferon gamma. This interference is accomplished by the VP24 and VP35 ebolavirus structural proteins. When a cell is infected with ebolavirus, receptors located in the cell's cytosol (such as RIG-I and MDA5) or outside of the cytosol (such as Toll-like receptor 3, Toll-like receptor 7, Toll-like receptor 8, and Toll-like receptor 9), recognize infectious molecules associated with the virus. After these receptors are activated, proteins including interferon regulatory factor 3 and interferon regulatory factor 7 start a signaling cascade that leads to the expression of type 1 interferons. Type 1 interferons are then released and bind to the IFNAR1 and IFNAR2 receptors expressed on the surface of the neighboring cell. Once interferon has bound to its receptors on the neighboring cell, the signaling proteins STAT1 and STAT2 are activated and move to the cell's nucleus. This triggers the expression of interferon-stimulated genes, which code for proteins that have antiviral properties. Ebolavirus' V24 protein prevents the STAT1 signaling protein in the neighboring cell from entering the nucleus and therefore prevents the creation of these antiviral proteins. A separate ebolavirus protein, known as VP35, directly inhibits the production of interferon-beta. The ability to inhibit these immune responses creates an environment in which Ebolavirus can quickly spread throughout the body.

sources : wikipedia

Cause

Ebola virus disease in humans is caused by four of five viruses in the genus Ebolavirus. The four are Bundibugyo virus (BDBV), Sudan virus (SUDV), Taï Forest virus (TAFV), and one called, simply, Ebola virus (EBOV, formerly Zaire Ebola virus). Ebola virus is the only member of the Zaire ebolavirus species and the most dangerous of the known EVD-causing viruses, as well as being responsible for the largest number of outbreaks.[20] The fifth virus, Reston virus (RESTV), is not thought to cause disease in humans, but has caused disease in other primates. These five viruses are closely related to marburgviruses.

Transmission

Life cycles of the Ebolavirus

The spread of Ebola between people occurs only by direct contact with the blood or body fluids of a person after symptoms have developed. Body fluids that may contain ebolaviruses include saliva, mucus, vomit, feces, sweat, tears, breast milk, urine, and semen. Entry points include the nose, mouth, eyes, or open wounds, cuts and abrasions. Contact with objects contaminated by the virus, particularly needles and syringes may also transmit the infection. The virus is able to survive on objects for a few hours in a dried state and can survive for a few days within body fluids.[23] Ebola virus may be able to persist in the semen of survivors for up to seven weeks after recovery, which could give rise to infections via sexual intercourse. Otherwise, people who have recovered are not infectious. The potential for widespread infections in countries with medical systems capable of observing correct medical isolation procedures is considered low. Usually when someone has symptoms, they are sufficiently unwell that they are unable to travel without assistance.

Handling infected dead bodies is a risk, including embalming. Because dead bodies are still infectious, traditional burial rituals may spread the disease. Nearly two thirds of the cases of Ebola infections in Guinea during the 2014 outbreak are believed to have been contracted via unprotected (or unsuitably protected) contact with infected corpses during certain Guinean burial rituals.

Healthcare workers treating those who are infected are at greatest risk of disease. This occurs when they do not wear appropriate protective clothing such as masks, gowns, gloves and eye protection. This is particularly common in parts of Africa where the health systems function poorly and where the disease mostly occurs. Hospital-acquired transmission has also occurred in African countries due to the reuse of needles. Some healthcare centers caring for people with the disease do not have running water. In the United States, spread has occurred due to inadequate isolation.

Airborne transmission has not been documented during EVD outbreaks. Transmission among rhesus monkeys via breathable 0.8–1.2 μm aerosolized droplets has been demonstrated in the laboratory. That airborne transmission does not appear to occur in humans may be due to there not being high enough levels of the virus in the lungs. Spread by water or food other than bushmeat has also not been observed, nor has spread by mosquitos or other insects.

Initial case

Bushmeat being prepared
for cooking in Ghana,  2013. Human
consumption of equatorial animals
in Africa in the form of bushmeat
has been linked to the transmission
of diseases to people, including Ebola.

While it is not entirely clear how Ebola initially spreads from animals to human, it is believed to involve direct contact with an infected wild animal or fruit bat. Wild animals other than bats capable of being infected include: a number of monkey, chimpanzees, gorillas, baboons and duikers. In Africa wild animals, including fruit bats are hunted to eat, being known as bushmeat.

Animals may become infected when they eat fruit already partially eaten by bats carrying the virus. Fruit production, animal behavior, and other factors may trigger outbreaks among animal populations.

It does appear that both domestic dog and pigs can also be infected with ebola viruses. Dogs when they carry the virus do not appear to develop symptoms, while pigs appear to be able to transmit the virus to at least some primates.

Reservoir

The natural reservoir for Ebola has yet to be confirmed; however, bats are considered to be the most likely candidate. Three types of fruit bats (Hypsignathus monstrosus, Epomops franqueti, and Myonycteris torquata) have been found to possibly carry the virus without getting sick. Whether or not other animals are involved in its spread is not known as of 2013. Plants, arthropods, and birds have also been considered as possible reservoirs as well.

Bats were known to reside in the cotton factory in which the first cases of the 1976 and 1979 outbreaks were observed, and they have also been implicated in Marburg virus infections in 1975 and 1980. Of 24 plant species and 19 vertebrate species experimentally inoculated with EBOV, only bats became infected. The bats displayed no clinical signs and is evidence that these bats are a reservoir species of the virus. In a 2002–2003 survey of 1,030 animals including 679 bats from Gabon and the Republic of the Congo, 13 fruit bats were found to contain EBOV RNA fragments.Antibodies against Zaire and Reston viruses have been found in fruit bats in Bangladesh, thus identifying potential virus hosts and signs of the filoviruses in Asia.

Between 1976 and 1998, in 30,000 mammals, birds, reptiles, amphibians and arthropods sampled from outbreak regions, no Ebola virus was detected apart from some genetic traces found in six rodents (Mus setulosus and Praomys) and one shrew (Sylvisorex ollula) collected from the Central African Republic. Further efforts; however, have not confirmed rodents as a reservoir. Traces of EBOV were detected in the carcasses of gorillas and chimpanzees during outbreaks in 2001 and 2003, which later became the source of human infections. However, the high lethality from infection in these species makes them unlikely as a natural reservoir.

Virology

Electron micrograph of an Ebola virus virion

Ebolaviruses contain single-strand, non-infectious RNA genomes. Ebolavirus genomes are approximately 19 kilobase pairs long and contain seven genes in the order 3'-UTR-NP-VP35-VP40-GP-VP30-VP24-L-5'-UTR. The genomes of the five different ebolaviruses (BDBV, EBOV, RESTV, SUDV, and TAFV) differ in sequence and the number and location of gene overlaps. Like all filoviruses, ebolavirions are filamentous particles that may appear in the shape of a shepherd's crook or in the shape of a "U" or a "6", and they may be coiled, toroid, or branched. In general, ebolavirions are 80 nanometers (nm) in width and may be as long as 14,000 nm. In general, the median particle length of ebolaviruses ranges from 974 to 1,086 nm (in contrast to marburgvirions, whose median particle length was measured at 795–828 nm), but particles as long as 14,000 nm have been detected in tissue culture.

Their life cycle begins with virion attachment to specific cell-surface receptors, followed by fusion of the virion envelope with cellular membranes and the concomitant release of the virus nucleocapsid into the cytosol. Ebolavirus' structural glycoprotein (known as GP1,2) is responsible for the virus' ability to bind to and infect targeted cells. The viral RNA polymerase, encoded by the L gene, partially uncoats the nucleocapsid and transcribes the genes into positive-strand mRNAs, which are then translated into structural and nonstructural proteins. The most abundant protein produced is the nucleoprotein, whose concentration in the cell determines when L switches from gene transcription to genome replication. Replication results in full-length, positive-strand antigenomes that are, in turn, transcribed into negative-strand virus progeny genome copy. Newly synthesized structural proteins and genomes self-assemble and accumulate near the inside of the cell membrane. Virions bud off from the cell, gaining their envelopes from the cellular membrane they bud from. The mature progeny particles then infect other cells to repeat the cycle. The Ebola virus genetics are difficult to study due to its virulent nature.

sources : wikipedia

Signs and symptoms

Signs and symptoms of Ebola.

The time between exposure to the virus and the development of symptoms of the disease is usually 2 to 21 days. Estimates based on mathematical models predict that around 5% of cases may take greater than 21 days to develop.

Symptoms usually begin with a sudden influenza-like stage characterized by feeling tired, fever, pain in the muscles and joints, headache, and sore throat. The fever is usually greater than 38.3 °C (100.9 °F). This is often followed by: vomiting, diarrhea and abdominal pain. Shortness of breath and chest pain may occur next along with swelling, headaches and confusion. In about half of cases the skin may develop a maculopapular rash (a flat red area covered with small bumps).

In some cases, internal and external bleeding may occur. This typically begins five to seven days after first symptoms. All people show some decreased blood clotting. Bleeding from mucous membranes or from sites of needle punctures is reported in 40–50% of cases. This may result in the vomiting of blood, coughing up of blood, or blood in stool. Bleeding into the skin may create petechiae, purpura, ecchymoses, or hematomas (especially around needle injection sites). There may also be bleeding into the whites of the eyes. Heavy bleeding is uncommon and if it occurs is usually within the gastrointestinal tract.

Recovery may begin between 7 and 14 days after the start of symptoms. Death, if it occurs, is typically 6 to 16 days from the start of symptoms and is often due to low blood pressure from fluid loss. In general, the development of bleeding often indicates a worse outcome and this blood loss can result in death. People are often in a coma near the end of life. Those who survive often have ongoing muscle and joint pain, liver inflammation, and decreased hearing among other difficulties.

sources : wikipedia

Ebola virus disease

Two nurses standing near Mayinga 

N'Seka, a nurse with Ebola virus disease 

in the 1976 outbreak in Zaire. N'Seka 

died a few days later.

Ebola virus disease (EVD; also Ebola hemorrhagic fever (EHF)) or simply Ebola is a disease of humans and other primates caused by ebolaviruses. Signs and symptoms typically start between two days and three weeks after contracting the virus, with a fever, sore throat, muscle pain and headaches. Then, vomiting, diarrhea and rash usually follows, along with decreased function of the liver and kidneys. At this time, generally, some people begin to bleed both internally and externally. Death, if it occurs, is typically six to sixteen days after symptoms appear and is often due to low blood pressure from fluid loss.

The virus is acquired by contact with blood or other body fluids of an infected human or other animal. This may also occur by direct contact with a recently contaminated item. Spread through the air has not been documented in the natural environment. Fruit bats are believed to be the normal carrier in nature, able to spread the virus without being affected. Humans become infected by contact with the bats or a living or dead animal that has been infected by bats. Once human infection occurs, the disease may spread between people as well. Male survivors may be able to transmit the disease via semen for nearly two months. To diagnose EVD, other diseases with similar symptoms such as malaria, cholera and other viral hemorrhagic fevers are first excluded. Blood samples are tested for viral antibodies, viral RNA, or the virus itself to confirm the diagnosis.

Outbreak control requires a coordinated series of medical services, along with a certain level of community engagement. The necessary medical services include rapid detection and contact tracing, quick access to appropriate laboratory services, proper management of those who are infected, and proper disposal of the dead through cremation or burial. Prevention includes decreasing the spread of disease from infected animals to humans. This may be done by only handling potentially infected bush meat while wearing protective clothing and by thoroughly cooking it before consumption. It also includes wearing proper protective clothing and washing hands when around a person with the disease. Samples of body fluids and tissues from people with the disease should be handled with special caution.

No specific treatment for the disease is yet available. Efforts to help those who are infected are supportive and include giving either oral rehydration therapy (slightly sweetened and salty water to drink) or intravenous fluids. This supportive care improves outcomes. The disease has a high risk of death, killing between 25% and 90% of those infected with the virus, averaging out at 50%. EVD was first identified in an area of Sudan (now part of South Sudan), as well as in Zaire (now the Democratic Republic of the Congo). The disease typically occurs in outbreaks in tropical regions of sub-Saharan Africa. From 1976 (when it was first identified) through 2013, the World Health Organization reported a total of 1,716 cases. The largest outbreak to date is the ongoing 2014 West African Ebola outbreak, which is currently affecting Guinea, Sierra Leone, and Liberia. As of 22 October 2014, 9,964 suspected cases resulting in the deaths of 4,881 have been reported. Efforts are under way to develop a vaccine.

sources : wikipedia