The team used massively parallel viral sequencing to gain information on the spread of the virus; 99 genome sequences were obtained from 78 patients (some genomes were sequenced twice) ahead of data analysis.
Worryingly, the team uncovered a total of 395 mutations (1), which sets this outbreak apart from previous outbreaks. Arguably of equal concern was the finding that molecular testing could prove inadequate – regions of the Sierra Leonean genomes used in five separate PCR-based assays did not match the PCR probes. With regards to transmission of the disease, no zoonotic sources were found to be involved in its spread. The genetic similarities suggested a single transmission from the natural reservoir, followed by extensive human-to-human transmission.
All of the genomic data has been made available to the research community as it is generated. The team hope that their work will aid diagnosis, the formation of public health strategies, and potentially guide research into Ebola treatments. “There’s nothing you should crowdsource more than an epidemic,” said co-author Pardis Sabeti.
The current outbreak of the virus in West Africa is the largest ever documented (2), with over 5,000 reported cases (3). Several authors of the genome study work at the Kenema Government Hospital (KGH), where the first case of Ebola in Sierra Leone was diagnosed in May of this year. According to the researchers, the outbreak in the country may have stemmed from the funeral of a traditional healer who had been treating patients with EVD in neighboring Guinea. The original Ebola patient at KGH had attended the funeral, and tracing turned up 13 more cases in women who were also present.
Study of the original patients and other infected individuals revealed that two genetically different strains of the virus appear to have spread to Sierra Leone from Guinea at around the same time – both were present in the original 14 patients and could have been contracted at the funeral. The loss of five co-authors of the study to EVD is a reminder of the risks faced by researchers; they were all experienced members of the hospital’s Lassa fever team and very familiar with the treatment of infectious disease. To date, Ebola has claimed the lives of more than 20 nurses, doctors and support staff at KGH. The World Health Organization (WHO) says that the number of medical staff now infected is “unprecedented” (4). More than 240 healthcare workers in West Africa have contracted the disease, and more than 120 have consequently died (5).
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References
- S. K. Gire et al., “Genomic Surveillance Elucidates Ebola Virus Origin and Transmission During the 2014 Outbreak”, Science, (2014). doi: 10.1126/science.1259657. Centre for Disease Control and Prevention: Outbreaks Chronology: Ebola hemorrhagic fever. http://www.cdc.gov/vhf/ebola/resources/outbreak-table.html. Centers for Disease Control – 2014 Ebola Outbreak in West Africa. http://www.cdc.gov/vhf/ebola/outbreaks/guinea/index.html. World Health Organization Situation Assessment, August 2014: “Unprecedented Number of Medical Staff Infected with Ebola”. http://www.who.int/mediacentre/news/ebola/25-august-2014/en/. G. Vogel, “Ebola’s Heavy Toll on StudyAuthors”, Science (2014) http://news.sciencemag.
