LETTER:Killer bugs whose time has come

The Ebola virus outbreak shows how vulnerable the world is to infectious disease, says Steve Connor

''It will be back,'' is how the American writer Richard Preston chose to end his lurid account of the Ebola virus in his book The Hot Zone. And, right on cue, Ebola has returned, once more in Zaire and once again in a hospital run by missionary nuns.

The parallel with the first recorded outbreak of Ebola virus is startling. Ebola emerged from its mysterious hiding place somewhere in the tropical jungles of Africa in 1976, when a schoolteacher attached to the Yambuku Mission Hospital, an ''upcountry'' clinic run by Belgian nuns, returned from a trip that took him across the Ebola river in northern Zaire. Feeling unwell, he asked the nuns for an injection. The five hypodermic syringes at the hospital were used on hundreds of other hospital patients, one needle for each syringe each day.

Within weeks the virus had swept through the hospital, the nuns and any families of patients who had managed to find their way home to die. By the time the virus had burnt itself out, nearly 300 people had died of an appalling array of illnesses and disease that Preston describes in lurid detail, from the black vomit and yellow, swollen livers to the red, blood-filled eyes and blue-black testicles.

The agent attacks every organ and tissue in the body, except muscle and bone, and transforms internal organs into a ''digested slime'', he writes. ''Your mouth bleeds, and you bleed around your teeth, and you may have haemorrhages from the salivary glands - literally every opening in the body bleeds, no matter how small.''

It can take days or even weeks for the first symptoms, headache and flu- like feverishness, to appear. But death comes within a few days once the virus takes a grip. The alimentary canal - from the mouth to the rectum - can become a particular target for Ebola. ''The surface of the tongue turns brilliant red and then sloughs off, and is swallowed or spat out,'' Preston says. ''It is said to be extraordinarily painful to lose the surface of one's tongue.''

No doubt the grotesque details of what Ebola can do to the human body have helped to fuel the intense publicity surrounding the current outbreak in Zaire. There is an understandable public fascination with mysterious diseases, especially those that turn human flesh to mush.

One headline on the Reuter news service yesterday - ''Beast Virus Turns Humans to Pulp'' - was reminiscent of that famous tabloid headline used to describe an outbreak of flesh-eating bacteria last year - ''Killer Bug Ate My Face''.

There is, however, little risk that Ebola will turn into the global threat posed by some of the other killer viruses and it would be inaccurate to suggest that it is ''more deadly than Aids'', as one newspaper reported yesterday. The Aids virus, HIV, is a much greater risk to humanity because of the long time - about 10 years - between infection and onset of disease. An outbreak of Ebola is relatively easy to contain, whereas HIV goes on a ''slow burn'' through an unwitting population.

Although Ebola can be extremely lethal, killing up to 90 per cent of those it infects, it is not easily transmitted. People have to come into close contact with infected body fluids, such as blood or vomit, before being at risk. Even if someone becomes infected, it is believed that intensive medical care can improve their chances considerably, as a Porton Down scientist infected in the Seventies and a Swiss scientist infected last year can both testify, by being alive and well today.

It is true in more ways than one that a hospital, especially one in Africa that can afford only the most rudimentary sterilisation equipment, is a dangerous place to be. A person dying of Ebola begins to lose an awful lot of blood and other body fluids and, theoretically, the tiniest drop can harbour myriad viruses that could infect someone who comes into close enough contact, such as a nurse or relative.

The virus, however, does not appear to be transmitted through airborne droplets, unlike influenza. Reusable syringes and hypodermic needles are undoubtedly a major cause of previous epidemics in Africa and may have played a significant role in the current outbreak in a hospital in the town of Kikwit, a couple of hundred miles east of the Zairean capital, Kinshasa.

Ebola is a level 4 virus, the most dangerous category, and scientists handling it have to work in full ''space suits'' and special high-security laboratories equipped with glove compartments similar to those used to handle highly radioactive material. Ebola is a ''filovirus'' because it looks like thin filaments or threads under the microscope.

Every virus needs a host organism to replicate because, being parasites, they have no life-support machinery of their own. Biologists used to think that it is in the virus's ''interests'' not to kill its hosts. Current thinking, however, has rejected this in favour of the idea that a virus's evolutionary success is based purely on its ability to survive and reproduce. If this involves wasting its host away, then so be it.

No one knows where Ebola livesbetween the periods when it emerges with such destructiveness in the human population. Scientists have in previous outbreaks attempted to extract Ebola from just about every living organism - insects, bats and even plants - that could have been harbouring the virus before it jumped the ''species barrier'' into humans. So far they have met with little success.

What they do know is that the world has become a more welcoming place for the re-emergence of infectious disease. Far more people are travelling freely around the globe and mega-cities are being built in the developing world which can provide a perfect environment for infections to spread. Finally, the tropical forests are being hacked down and colonised, bringing new viruses into contact with humans. Ebola will, indeed, be back.