Genetic factors could play an important role in whether people survive the Ebola virus, say US scientists.
A study of mice infected with the virus found they showed a number of different symptoms, with 19% remaining unaffected by the disease.
This could explain why some people recover from the illness while others die in pain, the scientists said.
Their study is published in the journal Science.
Scientists from the universities of Washington and North Carolina, and the National Institute of Health in Montana, examined mice they had infected with the same species of Ebola virus causing the current outbreak in West Africa.
Although all the mice lost weight in the first few days after infection, nearly one in five regained that weight within two weeks and showed no evidence of the disease.
But 70% of the mice became very ill, some showing signs of liver inflammation and a larger group having blood that took too long to clot.
These mice also had internal bleeding, swollen spleens and changes in liver colour.
They also had a greater than 50% chance of dying from the disease.
Angela Rasmussen, from the Katze Laboratory at the University of Washington, said the different ways in which the mice were affected mirrored the variety of symptoms seen in humans in the 2014 outbreak.
Recent Ebola survivors could have had immunity to this virus or a related virus which may have saved them, for example.
This would have meant the disease reacting in a particular way to a host's genes, which is seen with many other viruses.
Andrew Easton, professor of virology at the University of Warwick, said the study provided valuable information, but the data could not be directly applied to humans because they have a much larger variety of genetic combinations than mice.
He added: "The paper also does not assess the role of environmental factors that undoubtedly also play a role in the disease process such as the underlying health status of the at-risk population."
However, Prof Easton said the data suggested that "it may not be necessary to completely eliminate Ebola virus from the body during infection to ensure that there is no disease, and that reduction of virus growth in the body may offer alleviation from some aspects of the disease".
This suggests new treatments may not have to be as thorough as initially expected, he said.
Prof Jonathan Ball, professor of molecular virology at the University of Nottingham, said some of the study's discoveries regarding blood clotting were interesting.
"In this mouse model study, the finding that levels of expression of a gene involved in coagulation differs between mice showing different severity of disease symptoms is really intriguing.
"Of course, this is merely an association and needs to be explored more to know definitively how expression is controlled and how it might influence disease.
Prof Ball added: "It will also be important to see if a similar phenomenon is happening in humans."
Another study published in Science, on how best to stop the transmission of the Ebola virus, concluded that funerals were "super-spreader events".
Researchers from Yale University, Oregon State University and Liberia, said funeral practices - which often involve washing, touching and kissing of the bodies - had to end in order to bring the disease under control.
They also said aggressive steps should also be taken "to isolate cases and and better protect healthcare workers".