A new study by researchers from the Max Planck Insitute for Evolutionary Anthropology in Leipzig and Emory University in the United States, published in the journal PLoS Biology (November 2005), has shown that the outbreaks of the highly virulent Ebola Zaire virus are in no way random.

They are part of a wave of infection which has spread gradually across central Africa over the last three decades. This discovery offers new optimism about the possibility of controlling the effects of the Ebola virus on humans, as well as in highly endangered gorillas and chimpanzees.

In the study, genetic data from the virus were used to plot the spread of the Zaire strain across central Africa over the last three decades. Ebola Zaire has not only killed about 80 percent of human patients, but also tens of thousands of western lowland gorillas. It has thus become a major threat to the survival of apes in Africa.

Until now, the prospects of controlling the impact of Ebola have been dim. It has been assumed that Ebola Zaire was dormant over a long period of time across a large geographical strip of the central African forest, with outbreaks triggered by certain unknown environmental factors. The new study has shown that Ebola Zaire outbreaks are not caused by strains of virus which have been dormant for a long time at each place, but rather by a single strain of the virus that originated in the northern part of the Democratic Republic of the Congo (DRC) in the early 1970s.

The genetic analysis also showed the path of Ebola spread through the region. At first it took a western path toward central Gabon; then, it turned east into the Republic of the Congo (Congo-Brazzaville). This pattern of outbreak and spread is reflected in the genetic structure of the virus. The viruses of each outbreak descended from one of the outbreaks which took place just previously. The same pattern can also be seen in the temporal development of the outbreaks along the corridor of infection from DRC. The rate of spread along this corridor was very consistent, about 50 kilometers a year.

The consistency with which Ebola has spread has raised hopes of possibly controlling it. Targeted measures to do so - for example, vaccination - could be put into place shortly before the wave of infection arrived. Two experimental vaccines have succesfully protected laboratory monkeys from Ebola infection.

Peter Walsh, Max Planck researcher and main author of the study, says that "designing a vaccine which we can use on wild apes is a high conservation priority. Ebola has already devastated the world's two largest gorilla populations, along with other smaller ones. With the current rate of spread, Ebola could hit most of the rest of the large populations over the next five years. We are thus desperately looking for ways to put into place a vaccination programme to protect these apes."

Such a vaccination programme could also have advantages for humans, because many of the outbreaks in the region can be traced back to contact between people and infected ape carcasses.

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