The deadly Ebola virus that’s killed more than 600 people so far in West Africa may have been smoldering there for years and has almost certainly sickened people who thought they had something else, researchers say.
A new study of blood samples from people being treated for a serious, viral-like illness in years past in Guinea, Sierra Leone and Liberia suggests some of them could have been infected with Ebola. Now researchers are digging deeper to see if the virus has always been lurking there, just undetected.
It’s not a perfect test — the blood samples were several years old and had to be heat-treated so the researchers would be safe — but it’s a lead worth following up, said Randal Schoepp of the U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) team that did the research.
“It had been circulating there for a long time,” Schoepp told NBC News. “It just hadn’t gotten out of control or the right conditions weren’t there.”
Other researchers said the tests used are not 100 percent reliable, and more testing will be needed to see if they reflect what’s really happening. But it would be unlikely for a virus such as Ebola to appear completely out of the blue in a region. Experts suspect bats and perhaps other animals, too, carry the virus.
“It makes us realize that you don’t have to see an outbreak (to know a virus is circulating in an area),” Schoepp said. “In Africa, it is easy for a disease to smolder because there is so much disease.”
Ebola has killed at least 613 people in Guinea, Sierra Leone and West Africa in an outbreak that started in spring, according to the World Health Organization. It’s been diagnosed in 982, making for a mortality rate of more than 60 percent.
The WHO and Medecins Sans Frontieres (Doctors Without Borders) both say the outbreak is out of control. It killed 25 out of 28 nurses in a single hospital in Sierra Leone and patients are disappearing into the forest rather than seek treatment.
Ebola had never been seen in West Africa before, although there are plenty of other nasty infections, from malaria to dengue and, especially, Lassa fever. Lassa fever is caused by a virus unrelated to the one that causes Ebola but causes similar symptoms, include high fever, vomiting and internal and external bleeding.
Lassa is a far bigger problem than Ebola — it infects between 100,000 and 300,000 people a year in West Africa, killing 5,000, according to the U.S. Centers for Disease Control and Prevention.
So when someone shows up with a fever in West Africa, Lassa is a prime suspect.
Several U.S.-based organizations have been studying Lassa in Sierra Leone in the decade since a civil war there ended. But not everyone has Lassa or malaria — the majority of infections are never diagnosed.