Ebola: 3 questions about the killer virus

The highly contagious Ebola virus, which has killed almost 11,300 people in west Africa since December 2013 and has fuelled global alarm, is among the most dangerous ever identified.

- Where did it come from? -

Like AIDS, which began in Kinshasa in the 1920s before spreading worldwide, according to a recent study, Ebola was first identified in central Africa.

The tropical virus was named after a river in the Democratic Republic of Congo -- then known as Zaire -- where it came to light in 1976.

Five species have been identified to date (Zaire, Sudan, Bundibugyo, Reston and Tai Forest), the first being the most virulent with death rates that have reached 90 percent among humans.

The death rate in the current epidemic of haemorrhagic fever is thought to be around 67 percent according to the World Health Organization (WHO), although experts concede that many deaths, especially early in the epidemic, may have slipped under the radar.

- How is it transmitted? -

The virus' natural reservoir animal is probably the bat, which does not contract the disease itself.

Chimpanzees, gorillas, monkeys, forest antelope and porcupines are also suspected of having transmitted Ebola to humans.
Only one certified contact with an animal has been recorded in the current outbreak, however, early on in Guinea, following which it has been passed among humans.

Ebola is transmitted by contact with the blood, body fluids, secretions or organs of an infected or recently deceased person, but not by air.

Those infected do not become contagious until the symptoms appear. They then become more and more contagious until just after their death, which poses great risks during funerals.

Following an incubation period of between two and 21 days, five being the average according to a Swiss study, Ebola develops into a high fever, weakness, intense muscle and joint pain, headaches and sore throats.

That is often followed by vomiting and diarrhoea, skin eruptions, kidney and liver failure, and internal and external bleeding.

- How can it be treated? -

The WHO said Friday that the world "is on the verge of an effective Ebola vaccine" after Canadian drug VSV-EZEBOV is found in clinical trials in Guinea to provide 100-percent protection from the disease.

The drug, developed by the Public Health Agency of Canada and licensed to NewLink Genetics and Merck, may therefore become the first licensed vaccine against the disease for which there is also no approved treatment or cure.

Another candidate vaccine, made by the British pharmaceutical group GlaxoSmithKline with the American Institute of Allergy and Infectious Diseases (NIAID), has been undergoing tests in Liberia since February.

Because there is no approved drug treatment at present, patients are essentially re-hydrated.

A series of experimental treatments have nonetheless resulted in positive results among several patients.

The best known is ZMapp, a cocktail of three monoclonal (single cell) antibiotics developed through a Canadian/US partnership.

The US National Institutes of Health announced in February the commencement of a randomised controlled trial of ZMapp to be conducted in Liberia and the United States.

Early results from an Ebola trial using Avigan (favipiravir) showed in February it was somewhat effective at saving lives if given early in the illness, but not later.

The antiviral treatment is being developed by the Japanese company Toyama Chemical, and has been shown safe and effective against some other viruses including influenza, West Nile and yellow fever.

In the absence of a confirmed vaccine or cure, it is recommended that preventive measures be taken to stop the spread of Ebola -- notably through hand-washing and using gel or alcohol-based disinfectants.

A distance of several metres (yards) should also be kept from infected people or bodies, and healthcare providers must wear disposable protective clothing that includes masks and gloves.

Sites that have been contaminated must be disinfected.