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Researchers claim the Ebola virus disease (EVD) is rapidly and continually mutating, making it harder to diagnose and treat.

A study of the initial patients diagnosed with the virus in Sierra Leone revealed almost 400 genetic modifications.

And it could be detrimental not only to current treatments, but also to future vaccines that are in the works. 

Researchers at the Broad Institute in Massachusetts and Harvard University claim the Ebola virus (transmission electron micrograph image shown) is mutating rapidly. The findings show it is becoming more difficult to diagnose and treat. Future vaccines could also be less effective as mutations continue

The team of researchers, led by the Broad Institute in Massachusetts and Harvard University, analysed more than 99 Ebola virus genomes.

These were collected from 78 patients diagnosed with Ebola in Sierra Leona in the first 24 days of the outbreak.

Their findings, reported in the journal Science, could have important implications for rapid field diagnostic tests. 

The team found more than 300 genetic changes that make the 2014 Ebola virus genomes distinct from the viral genomes tied to previous Ebola outbreaks.

They also found variations in the genome sequence indicating that, from the samples analysed, the outbreak started from a single introduction into humans, subsequently spreading from person to person over many months. 

To accelerate response efforts, the research team released the full-length sequences on the National Center for Biotechnology Information's (NCBI's) DNA sequence database, in advance of publication. 

This means the data is available to the global scientific community.

'By making the data immediately available to the community, we hope to accelerate response efforts,' said co-senior author Dr Pardis Sabeti, a senior associate member at the Broad Institute and an associate professor at Harvard University. 

'Upon releasing our first batch of Ebola sequences in June, some of the world's leading epidemic specialists contacted us, and many of them are now also actively working on the data. We were honored and encouraged. 

'A spirit of international and multidisciplinary collaboration is needed to quickly shed light on the ongoing outbreak.'

This map shows the countries affected by Ebola as of 14 August 2014. The latest study was based on analysis of 78 patients diagnosed in the first 24 days of the outbreak in Sierra Leone. The scientists have released their findings to help efforts to halt the spread of Ebola

The 2014 Ebola outbreak is unprecedented both in its size and in its emergence in multiple populated areas.

Previous outbreaks had been localised, mostly to sparsely populated regions of Middle Africa, with the largest outbreak in 1976 reporting 318 cases.

By comparison, the 2014 outbreak has manifested in the more densely-populated West Africa, and since it was first reported in Guinea in March 2014, 2,240 cases have been confirmed with 1,229 deaths as of 19 August.

Dr Augustine Goba, Director of the Lassa Laboratory at the Kenema Government Hospital and a co-first author of the paper, identified the first Ebola virus disease case in Sierra Leone.

'We established surveillance for Ebola well ahead of the disease's spread into Sierra Leone and began retrospective screening for the disease on samples as far back as January of this year,' said Dr Goba. 

'This was possible because of our long-standing work to diagnose and study another deadly disease, Lassa fever. 

'We could thus identify cases and trace the Ebola virus spread as soon as it entered our country.'

Workers unload medical supplies to fight the Ebola epidemic from a USAID cargo flight on 24 August 2014 in Harbel, Liberia. International aid agencies and the Liberian government are struggling to keep up with the rapidly-expanding epidemic. The deadly virus has killed at least 1,400 people in West Africa

The research team increased the amount of genomic data available on the Ebola virus by four-fold and used the technique of 'deep sequencing' on all available samples. 

Deep sequencing is sequencing done enough times to generate high confidence in the results. 

In this study, researchers sequenced at a depth of 2,000 times on average for each Ebola genome to get an extremely close-up view of the virus genomes from 78 patients. 

This high-resolution view allowed the team to detect multiple mutations that alter protein sequences - potential targets for future diagnostics, vaccines and therapies.

The Ebola strains responsible for the current outbreak likely have a common ancestor, dating back to the very first recorded outbreak in 1976. 

The researchers also traced the transmission path and evolutionary relationships of the samples, revealing that the lineage responsible for the current outbreak diverged from the Middle African version of the virus within the last ten years and spread from Guinea to Sierra Leone by 12 people who had attended the same funeral.

The team's catalogue of 395 mutations may serve as a starting point for other research groups.

'We've uncovered more than 300 genetic clues about what sets this outbreak apart from previous outbreaks,' said Stephen Gire, a research scientist in the Sabeti lab at the Broad Institute and Harvard. 

'Although we don't know whether these differences are related to the severity of the current outbreak, by sharing these data with the research community, we hope to speed up our understanding of this epidemic and support global efforts to contain it.'

'There is an extraordinary battle still ahead, and we have lost many friends and colleagues already like our good friend and colleague Dr. Humarr Khan, a co-senior author here,' said Sabeti. 

'By providing this data to the research community immediately and demonstrating that transparency and partnership is one way we hope to honor Humarr's legacy. We are all in this fight together.'