The Ebola virus kills more than half of people it infects. A new study done with mice shows that genes may be one of the factors in who survives Ebola. Some people may be genetically resistant to Ebola; some people who are mildly resistant to Ebola tend to survive.

Other studies of Ebola outbreaks show that the difference in who survives Ebola and who dies may lie more in the person's body than in differences in the virus.

The research study was published yesterday, October 30, in the journal Science. The researchers took a group of genetically diverse mice that were specially bred to test human genetic response to viruses. The research was done at a secure lab designed to test biocontaminants. They found that some of the mice were completely resistant to the disease, some were infected but then recovered, and some succumbed to the disease.

This is further proof that there can be a range of immune responses to Ebola influenced by a person's genes.

Primates like monkeys are more genetically similar to humans, but running experiments with primates is much more expensive than using mice, because primates are much more costly to maintain. It is also more dangerous to work with monkeys that have been infected with Ebola.

However, the problem with studying Ebola in mice is that, although they can become infected and die from Ebola, they don't show traditional symptoms of the disease, like hemorrhagic fever. The mice in this study were special, though. They were genetically engineered to be more diverse than most mice used in laboratory studies, representing about 90% of the genetic variation in the overall mouse population.

This study shows that mice can become infected with the disease and show a range of symptoms similar to humans. This time, 40 percent of the mice died with symptoms of hemorrhagic fever and other symptoms similar to humans with Ebola. Another 40 percent of the mice died without experiencing any symptoms, and 19 percent of the mice did not die or experience any symptoms, but seemed able to resist the disease. All of the mice lost weight after being infected with the virus, but the 19 percent that seemed resistant regained all of the weight lost after two weeks.

"The frequency of different manifestations of the disease across the lines of these mice screened so far are similar in variety and proportion to the spectrum of clinical disease observed in the 2014 West African outbreak," said Angela Rasmussen, one of the lead researchers on this study.

The researchers are planning to use this study to test drugs that could be used against the Ebola virus.