Five co-authors of the latest study on Ebola were killed by the virus before their research was published, highlighting the huge risks undertaken by those working to combat its spread.

The study, published on Thursday, discovered the virus has mutated many times during the outbreak in West Africa, making establishing a treatment more difficult.

Mbalu Fonnie, Alex Moigboi, Alice Kovoma, Mohamed Fullah and Sheik Umar Khan worked with lead researchers at Harvard University to examine the current outbreak.

Science Mag said all five were experienced members of the Kenema Government Hospital’s (KGH) Lassa fever team. Lassa fever infections have similar symptoms to Ebola.

Their work sequenced the virus genomes from 78 patients and traced the outbreak in Sierra Leone to a funeral of a healer, which a pregnant Kenema Government Hospital Ebola patient and other women who were also infected had attended.

See the Ebola outbreak mapped Show all 7 1 /7 See the Ebola outbreak mapped See the Ebola outbreak mapped 25 March 2014 This outbreak of the Ebola virus first emerged in the Guéckédou region of Guinea, at a crossroads with both Liberia and Sierra Leone See the Ebola outbreak mapped 31 March On 31 March the WHO confirmed the outbreak was now international, spreading first into Liberia's northern-most Lofa region See the Ebola outbreak mapped 27 May The virus spread to Sierra Leone at the end of May - just as agencies were hoping the worst was over See the Ebola outbreak mapped 27 July In Sierra Leone the virus boomed, and then it spread to Nigeria when the Liberian diplomat Patrick Sawyer flew from Monrovia to Lagos See the Ebola outbreak mapped 9 August The Nigeria cases sparked fears around the world, and there have now been deaths in Spain and Saudi Arabia involving people who had travelled to West Africa. The numbers of cases continue to rise See the Ebola outbreak mapped 17-20 September In mid-September, Senegal confirmed its first case linked to the Ebola outbreak, a development the WHO described as a top priority emergency. Numbers of cases continued to grow exponentially in Guinea, Sierra Leone and Liberia, as experts warned they could number one million by January if not contained See the Ebola outbreak mapped 8 October Two cases of Ebola have now been reported in the US and Europe - the first times the virus has been contracted among health workers outside Africa

Two months before his death, Mr Khan had described the dangers of treating people with the disease, telling Reuters he feared for his life.

A doctor examines blood samples of Ebola (Getty)

He said: “I am afraid for my life, I must say, because I cherish my life. Health workers are prone to the disease because we are the first port of call for somebody who is sickened by disease. Even with the full protective clothing you put on, you are at risk.”

More than half of the 3,069 people infected by Ebola have died from the disease, which has spread across Sierra Leone, Liberia, Guinea, Nigeria and now Senegal.

The World Health Organisation has warned the current outbreak could infect up to 20,000 people before it ends.