Dec 26 (Reuters) - A new strain of the deadly Ebola virus that has infected 135 people and killed 36 in Uganda is spreading panic, although experts say the fears are overblown in a country ravaged by AIDS and malaria.

The last time Uganda was hit by an epidemic of Ebola, 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, usually fatal disease in humans and non-human primates (monkeys, gorillas, and chimpanzees) that has appeared sporadically since its initial recognition in 1976.

-- The Ebola virus is 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. The Zaire strain causes death in between 80 and 90 percent of all clinically ill cases. The Sudan strain kills 50 to 55 percent.

-- Genetic analysis of samples taken from some of the new victims show this new Uganda 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 25 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 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 in Uganda, including 224 deaths, making it the largest epidemic so far.

-- 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 is believed to have 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, editing by Tim Cocks)

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