A newly developed mouse model suggests that genetic factors are behind the mild-to-deadly range of reactions to the Ebola virus.
People exposed to Ebola vary in how the virus affects them. Some completely resist the disease, others suffer moderate to severe illness and recover, while those who are most susceptible succumb to bleeding, organ failure and shock.
In the new study, scientists led by the Katze Laboratory at the University of Washington Department of Microbiology described strains of laboratory mice bred to test the role of an individual's genetic makeup in the course of Ebola disease.
The scientists examined mice that they infected with a mouse form of the same species of Ebola virus causing the 2014 West Africa outbreak.
Interestingly, conventional laboratory mice previously infected with this virus died, but did not develop symptoms of Ebola hemorrhagic fever.
In the present study, all the mice lost weight in the first few days after infection. Nineteen per cent of the mice were unfazed.
They not only survived, but also fully regained their lost weight within two weeks. They had no gross pathological evidence of disease. Their livers looked normal.
Eleven per cent were partially resistant and less than half of these died. Seventy per cent of the mice had a greater than 50 per cent mortality, researchers found.
Nineteen per cent of this last group had liver inflammation without classic symptoms of Ebola, and thirty-four per cent had blood that took too long to clot, a hallmark of fatal Ebola hemorrhagic fever in humans.
Those mice also had internal bleeding, swollen spleens and changes in liver colour and texture.
The scientists correlated disease outcomes and variations in mortality rates to specific genetic lines of mice.
"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 virologists Angela Rasmussen.
While acknowledging that recent Ebola survivors may have had immunity to this or a related virus that saved them during this epidemic, researcher Michael Katze said, "our data suggest that genetic factors play a significant role in disease outcome."
In general, when virus infection frenzied the genes involved in promoting blood vessel inflammation and cell death, serious or fatal disease followed.
On the other hand, survivors experienced more activity in genes that order blood vessel repair and the production of infectionfighting white blood cells.