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What is Ebola? A look at where the disease originated, and how it’s evolved

In less than four decades since emerging from the jungles of Central Africa, Ebola has become one of the modern world's most notorious diseases.

Over the past year, the worst Ebola outbreak in history has swept across West Africa, killing more than 6,000 people in a highly publicized public health crisis. In total, Ebola is responsible for more than 7,700 confirmed deaths since its discovery – a relatively small number compared to viruses such as Lassa fever or HIV, which kill thousands annually in Sub-Saharan Africa. Still, Ebola's high mortality rate, often gruesome symptoms, and lack of a cure have made it infamous.

Ebola virus disease was first identified in 1976, when simultaneous outbreaks occurred near the village of Yambuku, Democratic Republic of the Congo, and the South Sudanese town of Nzara. The outbreaks would claim more than 430 lives in these regions at a 72 per cent mortality rate. While the outbreaks were approximately 700 kilometres apart, they were caused by two unique strains of the virus.

The World Health Organization (WHO) counts more than two dozen Ebola outbreaks since 1976, all originating in Africa. The most recent outbreak has been by far the largest in scope, and is responsible for 80 per cent of the all-time recorded Ebola casualties. Two people in Russia died after accidentally contracting the disease during laboratory research, while one strain of the virus, carried by pigs and monkeys, has led to asymptomatic human infections in the Philippines and the U.S.

Belgian microbiologist Peter Piot was among the first to identify the virus in the Congolese jungle. Rather than to name it after its village of origin, and forever cast a shadow over Yambuku, he named it for the Ebola River about 60 kilometres away.

Researchers believe a local species of fruit bat is a natural host of the virus, and Ebola was spread to other animals through bites and feces. According to WHO, the virus was likely introduced to humans through contact with the bodily fluids of infected apes, antelopes and other animals found ill or dead in the rainforest.
Among humans, the virus is passed much the same way. Direct contact with blood, secretions, organs or other bodily fluids is required, and can only occur when the infected person is showing symptoms.

Once symptoms occur, Ebola is highly infectious, and victims remain contagious even after death. This makes Ebola particularly difficult to contain in outbreak situations. In fact, WHO linked as many as 60 per cent of the 2014 Ebola cases in Guinea with traditional burial practices that involve contact with the body.

After infection, Ebola has an incubation period of two to 21 days before symptoms occur. According to the Centers for Disease Control and Prevention (CDC), those symptoms can include fever, headache, muscle pain, weakness and fatigue, and unexplained hemorrhaging, which can occur from the mouth, rectum, eyes, nose and ears. The graphic nature of this bleeding has helped solidify Ebola's gruesome reputation. Death, which occurs in roughly 50 per cent of confirmed cases, is usually caused by organ failure or hypovolemic/hemorrhagic shock, a life-threatening condition that results when a person loses a large proportion of their body’s blood or fluid supply.

While there are no proven vaccinations or cure for Ebola, the scale of the 2014 outbreak in West Africa has hastened attempts to develop them. Progress is being made at unprecedented rates, as clinical trials that would normally take years are being conducted in weeks.

Human trials have begun for two vaccines – one designed by the Public Health Agency of Canada, and the other by the National Institutes of Health in the U.S. Potential vaccinations are also in development in at least seven other countries. Médecins Sans Frontières/Doctors Without Borders facilities in Guinea and Liberia have also been conducting clinical trials of three potential treatments for Ebola since November. Results from these trials are expected by March 2015.

For now, chances of surviving Ebola virus disease significantly improve with early, supportive care, including rehydration and maintaining oxygen status and blood pressure, according to CDC.