A team at the Howard Hughes Medical Institute in the US state of Michigan have developed the first vaccine able to protect against the deadly Ebola virus.

The virus causes sporadic outbreaks of fever which usually kill most of those infected.

Although the vaccine has so far only been tested in animals, there is considerable excitement because the research team seem to have cracked the basic problem involved in protecting against Ebola virus. This report from John Newell of BBC Science.

Ebola virus and its close relative, the Marburg virus, are notorious because they cause death so quickly.

Electron micrograph of Ebola Zaire virus.

The first reported Ebola outbreak occurred in Sudan in 1976 and since then, about 1,000 cases have been reported worldwide, with more than half of those infected dying within days.

The most recent large epidemic occurred two years ago in the Democratic Republic of Congo, formerly Zaire.

Dr Gary Nabel, who leads the research team developing the new vaccine, describes the symptoms.

"It's a virus that in a very short period of time can go from causing simple flu-like symptoms to a really massive bleeding disorder and circulatory collapse. It also spreads readily: it's highly infectious.

"And it spreads before symptoms are apparent, so it can be somewhat problematic to contain.

"From the public health standpoint, it's of greater concern because we don't know what its reservoir is (where it hides in nature), so we don't really know where to look for it, and where to try to eradicate it and keep it from spreading."

The continuing increase in travel and tourism presents an ever-increasing risk that outbreaks of Ebola virus may be spread anywhere in the world, with no effective treatment and no protective vaccine available. Only rigid isolation can protect against infection.

So far large-scale outbreaks have been prevented by the fact that the virus does not appear to be spread through the air by coughing, but only through contact with infected vomit, excrement or blood.

But public health officials' nightmare is that an outbreak could get well under way and spread widely before being recognised for what it is.

Attempts have been made to develop a vaccine which could protect against Ebola virus, by stimulating the immune system of vaccinated people to attack and kill the virus if they came in contact with it.

But, as Gary Nabel explains, the virus is very good at evading the immune system.

"The host (infected person) really has two ways in which it can respond to virus infection; it can create an inflammatory response which will eliminate the virus or it can develop an immunological memory which can recognise the virus and rapidly mobilise the immune system to eliminate the virus.

"Ebola has evolved to circumvent (evade) both these host protective devices."

Gary Nabel had to devise a vaccine which would leave the human immune system able not only to recognise and attack the Ebola virus but also to prevent it dodging the response.

He did it by making a new kind of vaccine called a DNA vaccine which contains nothing but a few genes taken from the virus.

When this is injected into someone, the genes cause cells in the person's body to produce virus material in the same way as it would if it were infected with the virus itself.

Because only a few genes are used, this kind of vaccination doesn't cause an infection, but because it so resembles an infection it does stimulate immunity very strongly and doesn't allow the real virus to escape.

Animal tests in rodents - guinea pigs - showed the vaccine completely protected them against normally lethal doses of Ebola virus. Now Gary Nabel is planning the next stage of the test programme.

"The fact that we were able to generate immunity is certainly encouraging since until now there has not been a vaccine that has worked in any animal model.

The next step is to test it in primates and there can be difference between primates and guinea pigs, which is why we want to test in a non-human primate before proceeding to trials in man.

The subjects for human trials would probably be medical and laboratory workers in high-risk areas who might be exposed to the virus."

Trials on primates are expected next year and if all goes well the first human tests could begin in a year or two after that.

Nothing is certain yet but there is now, for the first time, real hope of defending effectively against one of the authentic medical nightmares of modern times.
 

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