Ebola virus disease (EVD) or Ebola hemorrhagic fever (EHF) is a disease of humans and other primates caused by an ebolavirus. Symptoms start two days to three weeks after contracting the virus, with a fever, sore throat, muscle pain and headaches. Typically, vomiting, diarrhea and rash follow, along with decreased functioning of the liver and kidneys. Around this time, affected people may begin to bleed both within the body and externally.

Signs and symptoms

Signs and symptoms of Ebola usually begin suddenly with an influenza-like stage characterized by fatigue, fever, headaches, joint, muscle and abdominal pain. Vomiting, diarrhea and loss of appetite are also common. Less common symptoms include the following: sore throat, chest pain, hiccups, shortness of breath and trouble swallowing. The average time between contracting the infection and the start of symptoms (incubation period) is 8 to 10 days, but it can vary between 2 and 21 days. Skin manifestations may include a maculopapular rash (in about 50% of cases). Early symptoms of EVD may be similar to those of malaria, dengue fever or other tropical fevers, before the disease progresses to the bleeding phase.

In 40–50% of cases, bleeding from puncture sites and mucous membranes (e.g. gastrointestinal tract, nose, vagina and gums) has been reported. In the bleeding phase, which typically starts 5 to 7 days after first symptoms internal and subcutaneous bleeding may present itself through reddening of the eyes and bloody vomit. Bleeding into the skin may create petechiae, purpura, ecchymoses and hematomas (especially around needle injection sites). Types of bleeding known to occur with Ebola virus disease include vomiting blood, coughing it up or blood in the stool. Heavy bleeding is rare and is usually confined to the gastrointestinal tract. In general, the development of bleeding symptoms often indicates a worse prognosis and this blood loss can result in death. All people infected show some symptoms of circulatory system involvement, including impaired blood clotting. If the infected person does not recover, death due to multiple organ dysfunction syndrome occurs within 7 to 16 days (usually between days 8 and 9) after first symptoms.

Causes

EVD is caused by four of five viruses classified in the genus Ebolavirus, family Filoviridae, order Mononegavirales. The four disease-causing viruses 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 sole member of the Zaire ebolavirus species, and the most dangerous of the known Ebola disease-causing viruses, as well as being responsible for the largest number of outbreaks. The fifth virus, Reston virus (RESTV), is not thought to be disease-causing in humans. The five Ebola viruses are closely related to the Marburg viruses.

Transmission

It is not entirely clear how Ebola is spread. EVD is believed to occur after an ebola virus is transmitted to an initial human by contact with an infected animal’s body fluids. Human-to-human transmission can occur via direct contact with blood or bodily fluids from an infected person (including embalming of an infected dead person) or by contact with contaminated medical equipment, particularly needles and syringes. The potential for widespread EVD infections is considered low as the disease is only spread by direct contact with the secretions from someone who is showing signs of infection. The quick onset of symptoms makes it easier to identify sick individuals and limits a person’s ability to spread the disease by traveling. Because dead bodies are still infectious local traditional burial rituals may spread the disease. Semen may be infectious in survivors for up to 50 days.
Medical workers who do not wear appropriate protective clothing may also contract the disease. In the past, hospital-acquired transmission has occurred in African hospitals due to the reuse of needles and lack of universal precautions.
Airborne transmission has not been documented during EVD outbreaks. They are, however, infectious as breathable 0.8– to 1.2-μm laboratory-generated droplets. The virus has been shown to travel without contact from pigs to nonhuman primates, although the same study failed to achieve transmission in that manner between primates.
Bats drop partially eaten fruits and pulp, then land mammals such as gorillas and duikers feed on these fallen fruits. This chain of events forms a possible indirect means of transmission from the natural host to animal populations, which has led to research towards viral shedding in the saliva of bats. Fruit production, animal behavior, and other factors vary at different times and places that may trigger outbreaks among animal populations.

Prevention

Infection control

Ebola viruses are contagious, with prevention predominantly involving behavior changes, proper full-body personal protective equipment, and disinfection. Techniques to avoid infection involve not contacting infected blood or secretions, including from those who are dead. This involves suspecting and diagnosing the disease early and using standard precautions for all patients in the healthcare setting. Recommended measures when caring for those who are infected include isolating them, sterilizing equipment, and wearing protective clothing including masks, gloves, gowns, and goggles. Hand washing is important but can be difficult in areas where there is not even enough water for drinking. In an ongoing (2014) outbreak of Ebola in West Africa, infection control items, even soap, are in critical short supply. When soap is difficult to obtain during emergencies, the WHO promotes using substitutes such as clean ash (or sand).

The Ebola virus can be eliminated with heat (heating for 30 to 60 minutes at 60 °C or boiling for 5 minutes). On surfaces, some lipid solvents such as some alcohol-based products, detergents, sodium hypochlorite (bleach) or calcium hypochlorite (bleaching powder), and other suitable disinfectants at appropriate concentrations can be used as disinfectants.

Due to lack of proper equipment and hygienic practices, large-scale epidemics have occurred mostly in poor, isolated areas without modern hospitals or well-educated medical staff. Traditional burial rituals, especially those requiring washing or embalming of bodies, should be discouraged or modified. Airline crews are instructed to isolate anyone who has symptoms resembling Ebola virus.

Quarantine

Quarantine, also known as enforced isolation, is usually effective in decreasing spread. Governments often quarantine areas where the disease is occurring or individuals who may be infected. In the United States, the law allows quarantine of those infected with Ebola. The lack of roads and transportation may help slow the disease in Africa. During the 2014 outbreak, Liberia closed schools.

Vaccine

No vaccine is currently available for humans. The most promising candidates are DNA vaccines or vaccines derived from adenoviruses, vesicular stomatitis Indiana virus (VSIV) or filovirus-like particles (VLPs) because these candidates could protect nonhuman primates from ebolavirus-induced disease. DNA vaccines, adenovirus-based vaccines, and VSIV-based vaccines have entered clinical trials.
Vaccines have protected nonhuman primates. Immunization takes six months, which impedes the counter-epidemic use of the vaccines. Searching for a quicker onset of effectiveness, in 2003, a vaccine using an adenoviral (ADV) vector carrying the Ebola spike protein was tested on crab-eating macaques. Twenty-eight days later, they were challenged with the virus and remained resistant. A vaccine based on attenuated recombinant vesicular stomatitis virus (VSV) vector carrying either the Ebola glycoprotein or the Marburg glycoprotein in 2005 protected nonhuman primates, opening clinical trials in humans. The study by October completed the first human trial, over three months giving three vaccinations safely inducing an immune response. Individuals for a year were followed, and, in 2006, a study testing a faster-acting, single-shot vaccine began; this new study was completed in 2008. Trying the vaccine on a strain of Ebola that more resembles one that infects humans is the next step. On 6 December 2011, the development of a successful vaccine against Ebola for mice was reported. Unlike the predecessors, it can be freeze-dried and thus stored for long periods in wait for an outbreak. An experimental vaccine made by researchers at Canada’s national laboratory in Winnipeg was used, in 2009, to pre-emptively treat a German scientist who might have been infected during a lab accident. However, actual EBOV infection could never be demonstrated without a doubt. Experimentally, recombinant vesicular stomatitis Indiana virus (VSIV) expressing the glycoprotein of EBOV or SUDV has been used successfully in nonhuman primate models as post-exposure prophylaxis. The CDC’s recommendations are currently under review.

Laboratory

Ebola viruses are World Health Organization Risk Group 4 pathogens, requiring biosafety level 4-equivalent containment. Laboratory researchers must be properly trained in BSL-4 practices and wear proper personal protective equipment.

Treatment

No ebolavirus-specific treatment exists. Treatment is primarily supportive in nature and includes minimizing invasive procedures, balancing fluids and electrolytes to counter dehydration, administration of anticoagulants early in infection to prevent or control disseminated intravascular coagulation, administration of procoagulants late in infection to control bleeding, maintaining oxygen levels, pain management, and the use of medications to treat bacterial or fungal secondary infections. Early treatment may increase the chance of survival. A number of experimental treatments are being studied.

In the United States, in the setting of a phase I clinical trial, the FDA’s animal efficacy rule can be used to demonstrate reasonable safety to obtain permission to treat people who are infected with Ebola. The animal efficacy rule exists, because the normal path for testing the safety and efficacy of drugs is not possible for diseases caused by dangerous pathogens or toxins. The FDA has allowed two drugs, ZMapp and an RNA interference drug called TKM-Ebola, to be used in people infected with Ebola under these programs during the 2014 outbreak.

Prognosis

The disease has a high mortality rate: often between 50 percent and 90 percent. As of April 2014, information from WHO across all occurrences to date puts the overall fatality rate at 60%-65%. There are indications based on variations in death rate between countries that early and effective treatment of symptoms (e.g., supportive care to prevent dehydration) may reduce the fatality rate significantly. If an infected person survives, recovery may be quick and complete. Prolonged cases are often complicated by the occurrence of long-term problems, such as inflammation of the testicles, joint pains, muscle pains, skin peeling, or hair loss. Eye symptoms, such as light sensitivity, excess tearing, iritis, iridocyclitis, choroiditis, and blindness have also been described. EBOV and SUDV may be able to persist in the semen of some survivors for up to seven weeks, which could give rise to infections and disease via sexual intercourse.

Source : Wikipedia

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