The Ebola virus plaguing West African nations, where almost 500 people have died since January, is one of the deadliest known to man and can kill victims within days.
New data from the United Nations this week confirmed this is the worst ever outbreak of this strain of haemorrhagic fever, first identified 38 years ago in the Democratic Republic of Congo, then Zaire.
Ebola is one of several viruses responsible for haemorrhagic fever.
No medicine or vaccine
The latest figures released by the World Health Organisation (WHO) indicate that haemorrhagic fevers have killed 467 people in Guinea, Liberia and Sierra Leone. Of those, 291 were confirmed Ebola cases.
The WHO data show a total 759 cases of fever, of which 544 are known to be of the Ebola strain.
No medicine or vaccine exists for the tropical virus, named after a small river in the DRC.
Read: Haemorrhagic diseases
Five "species" of Ebola have been identified so far, and have been named Bundibugyo, Sudan, Zaire, Tai Forest and Reston.
The first three are particularly dangerous, with fatality rates of up to 90 percent.
The Reston species has also been identified in China and the Philippines, but no associated deaths have been reported in those countries to date.
Severe fever and muscle pain
A breakdown by the WHO of the overall death toll from haemorrhagic fevers in West Africa now stands at 303 in Guinea, 99 in Sierra Leone and 65 in Liberia.
Ebola causes severe fever and muscle pain, weakness, vomiting and diarrhoea – in some cases shutting down organs and causing unstoppable bleeding.
It is a so-called filovirus, transmitted through contact with the blood, body fluids, secretions or organs of an infected person.
Experts say that while extremely virulent, the virus can be contained because it kills victims faster than it spreads.
Read: West African Ebola epidemic 'out of control'
The incubation period between exposure and the first symptoms varies from two to 21 days.
The virus has been known to spread at burials where mourners touch the body, but doctors and nurses have also fallen ill after failing to take adequate precautions.
Even testing blood specimens for the disease presents "an extreme risk", the WHO has warned, and is done only in the strictest containment conditions.
The virus's natural host in Africa is thought to be a species of rainforest bat, while another concentration has been found in the western Pacific region.
People have contracted the virus after handling both dead and living chimpanzees, gorillas, monkeys, forest antelope and porcupines.
For now, the only approach is to isolate patients and promptly bury the dead, says the WHO.
Hospital staff should use gloves, masks and goggles, and disinfect religiously.
"Several potential vaccines are being tested but it could be several years before any are available," according to a WHO factsheet.
"A new drug therapy has shown some promise in laboratory studies and is currently being evaluated."
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