(for related story see UGANDA-EBOLA/ or click [ID:nL06917045]

Dec 6 (Reuters) - A new strain of the deadly Ebola virus is thought to have infected 93 people and killed at least 22 in Uganda, including a doctor and three other medical staff looking after patients, a health official said on Thursday.

The last time Uganda was hit by an epidemic of Ebola -- a disease in which those infected often bleed to death -- 425 people caught it in 2000. Just over half of them died.

Here are some key facts on Ebola:

* ORIGINS:

-- Ebola haemorrhagic fever (EHF) is a severe, often fatal disease in humans and non-human primates (monkeys, gorillas, and chimpanzees) that has appeared sporadically since its initial recognition in 1976.

-- The disease is caused by infection with Ebola virus, named after a river in the Democratic Republic of Congo (formerly Zaire) in Africa, where it was first recognised.

-- The Ebola virus comprises four distinct subtypes: Zaire, Sudan, Côte d'Ivoire and Reston. Three subtypes, occurring in the Democratic Republic of Congo, Sudan and the Ivory Coast, have been identified as causing illness in humans. EHF is a febrile haemorrhagic illness which causes death in between 50 and 90 percent of all clinically ill cases.

-- Genetic analysis of samples taken from some of the new victims show this virus is a previously unrecorded type of Ebola, making it a fifth strain, U.S. and Ugandan health officials have said. The unusually low death rate of this type -- at roughly 22 percent -- shows it is less lethal than previous epidemics.

* SYMPTOMS:

-- Ebola is often characterised by the sudden onset of fever, intense weakness, muscle pain, headache and sore throat.

-- This is often followed by vomiting, diarrhoea, rash, impaired kidney and liver function and, in some cases, both internal and external bleeding.

-- The fever has an incubation period of two to 21 days.

-- No specific treatment or vaccine is yet available.

* TRANSMISSION:

-- The Ebola virus is transmitted by direct contact with the blood, secretions, organs or other bodily fluids of infected people.

-- Burial ceremonies where mourners have direct contact with the body of the deceased person can play a significant role in the transmission of Ebola. Health care workers have frequently been infected while treating Ebola patients.

* MAJOR OUTBREAKS:

-- Between June and November 1976, EHF infected 284 people in Sudan, causing 151 deaths. In the Democratic Republic of Congo, there were 318 cases and 280 deaths in late 1976.

-- Between September 2000 and January 2001, the Sudan subtype of the Ebola virus infected 425 people, including 224 deaths, making it the largest epidemic so far of Ebola.

-- From October 2001 to December 2003, several EHF outbreaks of the Zaire subtype, were reported in Gabon and the Republic of Congo, with a total of 302 cases and 254 deaths.

-- Earlier this month, health officials in Democratic Republic of Congo declared the end of an Ebola outbreak, which it is believed has killed up to 187 people over 8 months. People began falling ill in April in the village of Kampungu in Western Kasai province with Ebola-like symptoms.

Sources: Reuters/ U.S. Centers for Disease Control and Prevention/ World Health Organisation. (Writing by David Cutler, London Editorial Reference Unit)

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