For the first time, scientists have been able to follow the spread of an Ebola outbreak almost in real time, by sequencing the virus’ genome from people in Sierra Leone. The findings, published Thursday in the journal Science, offer new insights into how the outbreak started in West Africa and how fast the virus is mutating. An international team of researchers sequenced 99 Ebola genomes, with extremely high accuracy, from 78 people diagnosed with Ebola in Sierra Leone in June. The Ebola genome is incredibly simple. It has just seven genes. By comparison, we humans have about 20,000 genes. “In general, these viruses are amazing because they are these tiny things that can do a lot of damage,” says Pardis Sabeti, a computational biologist at Harvard University and the lead author of the study. Hidden inside Ebola’s tiny genome, she says, are clues to how the virus spreads among people — and how to stop it. “As soon as the outbreak happened and was reported in Guinea,” she says, “two members of my lab flew out and worked to set up the diagnostics to pick it up in Sierra Leone.” The team helped to find the first Ebola cases in Sierra Leone. They also immediately shipped diagnostic samples from the patients back to the U.S. and started sequencing the viruses’ genomes. “We had 20 people in my lab working around-the-clock,” Sabeti says. Their furious pace paid off. After just a week or so, the team had decoded gene sequences from 99 Ebola viruses. The data offered a treasure-trove of information about the outbreak. For starters, the data show that the virus is rapidly accumulating new mutations as it spreads through people. “We’ve found over 250 mutations that are changing in real time as we’re watching,” Sabeti says.

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