By Kate Kelland, Health and Science Correspondent

LONDON, March 25 (Reuters) - Peter Piot was 27, newly qualified and working in a microbiology lab in Antwerp when he received a flask of human blood contaminated with a mysterious pathogen that had been killing people in the forests of Zaire.

If he'd known then what he was to discover - that inside was Ebola, one of the most lethal infectious diseases now known in humans - he would have taken more safety precautions.

As it was, Piot and his colleagues wore only latex gloves and white cotton lab coats as they unscrewed the top, took out its contents - vials of infected blood taken from a Flemish nun in Zaire, stored in a blue thermos flask and couriered to Belgium on a passenger plane - and began analysing them.

"Looking back, that was probably quite irresponsible. But we didn't know then what we were dealing with," the now 65-year-old said in an interview from his office at the London School of Hygiene and Tropical Medicine, where he is director.

"These are dangerous moments - particularly when you don't know what you've got. Such blood can contain very high levels of virus."

"SPECTACULAR VIRUS"

That tale dates from Belgium in 1976, when Piot and his team became the co-discoverers of Ebola. The young Belgian scientist then went to Zaire, now Congo, in central Africa to work in the rainforests among dying villagers and missionaries to collect samples and investigate the epidemic.

Yet almost four decades on, the disease Piot describes as "a spectacular virus - and one of the most lethal infections you can think of", has continued to rise up in the region, causing frightening but sporadic outbreaks that kill poor and vulnerable people with gruesome haemorrhagic fevers.

In Guinea, health authorities said on Monday that an outbreak there - the first known in a west Africa country - already involves scores of suspected cases.

The Geneva-based World Health Organisation said on Tuesday Guinea had reported at least 86 cases reported, including 59 deaths.

Six suspected Ebola cases, including five deaths, in neighbouring Liberia were also under investigation, it said.

Piot says he's saddened and frustrated by this and other outbreaks - partly because they should be easy to prevent, or at least to contain, and partly because the scientific detective work behind the Ebola virus has not yet revealed its main host.

"What we're seeing is a pattern that's been repeated in nearly every single Ebola outbreak," he told Reuters.

"It started in people who live in the forest, or in close contact with it, and it's then transmitted around hospitals....and then spreads further either at funerals or in households though close contact."

NO TREATMENT OR VACCINE

The virus initially causes a raging fever, headaches, muscle pain and conjunctivitis, before moving to severe phases that bring on vomiting, diarrhoea and internal and external bleeding. It kills up to 90 percent of those who become infected.

That there is no treatment or vaccine against Ebola suggests people are helpless in the face of this vicious virus, but Piot insists that is not the case.

"Fundamentally, Ebola is easy to contain," he said. "It's not a question of needing high technology."

"It's about respecting the basics of hygiene, and about isolation, quarantine and protecting yourself - in particular protecting healthcare workers, because they are very exposed."

The problem in Guinea, and in other countries in Africa where Ebola has reared up in the past few decades, is that health systems are in bad shape, he said, communications are limited, and the people are fairly mobile and very poor.

As a doctor and researcher whose life has been dedicated to the pursuit of deadly viruses - (after his Ebola discovery Piot became one of the world's leading scientific experts on HIV and AIDS) - Piot is also frustrated that scientists have not yet been able to pin down the main host of this lethal fever.

While the virus is known to be transmitted to people from wild animals, before spreading in humans through person-to-person transmission, its main animal host - or what virologists often call the "reservoir" of a virus - is not totally clear.

Piot, like others, suspects fruit bats of the Pteropodidae family are the most likely natural host, yet the uncertainty leaves scientists unable to get ahead of fresh outbreaks.

"This is a virus that is highly unpredictable," he said. "This time it popped up in Guinea where it has never been detected before.

"Why there? Why now? That's what I find frustrating. If we knew for sure the host of this virus, we could do more to say where people are more at risk." (Editing by Raissa Kasolowsky)

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