The recent Ebola outbreak in West Africa has claimed more than 11,000 lives as of May 31, 2015. This outbreak was caused by the Makona strain of the Ebola virus. But, the Ebola outbreak caused by the Mayinga strain in 1976 was limited, killing 318 people in the Democratic Republic of Congo, the former Zaire. The deadliest case with this strain came in Uganda in 2000 causing the death of 425 people. However, a new study has revealed that the Ebola strain that ravaged West Africa last year is less virulent than the first one that appeared in 1976.
The earlier outbreaks possibly had a weaker impact because they happened in rural, sparsely populated areas. The results of the test on monkeys by scientists at the National Institutes of Health (NIH) are important because they suggest the virus is not becoming more severe. The study said, "In fact, the current virus has a decreased ability to cause disease in their animal model compared to the 1976 strain."
In the NIH experiment, two groups of monkeys were infected with one or the other strain of the Ebola virus. It was observed that in three days both were spreading the virus, and the ones with the Mayinga strain developed a rash on day four and became extremely ill on days five and six. But the monkeys with the Makona strain did not get rashes before the sixth day, and severe symptoms did not appear until day seven.
Furthermore, liver damage, which is a typical result of Ebola infection, appeared in the Makona-strain-infected monkeys two days later than the ones with the Mayinga strain. Also, the immune systems of the animals with the weaker Makona strain produced around three times as much virus-fighting protein as those with the Mayinga strain did.
The virologists who conducted this study plan to do more research on how immune systems react to both strains of Ebola. They believe that at least seven days are needed after infection to mount an effective response. This response does not seem to happen in monkeys infected with the Mayinga strain because the Ebola disease progresses too quickly.