UCLA researchers have discovered that Ebola survivors retain immunity to the virus even 40 years after contracting the disease.
In a study published in December, UCLA researchers led by Anne Rimoin, associate professor of epidemiology, demonstrated that survivors of the 1976 Ebola outbreak in Central Africa still have antibodies against the Ebola virus. The presence of reactive antibodies, a component of the immune system important for long-term resistance to diseases, suggests that Ebola vaccines may prevent future outbreaks, according to the study.
“There are now 10 to 15 thousand Ebola survivors in West Africa, but no one’s looked at the long-term health consequences of Ebola before,” Rimoin said. “We’ve documented for the first time that there’s long-lasting, durable immunity to Ebola.”
Antibodies stop bacteria and viruses from infecting human cells and mark the foreign invaders for destruction by other parts of the immune system. Long-term resistance to diseases such as Ebola relies on the presence of antibodies that can recognize and react with foreign invaders.
The research team took blood samples from 14 Ebola survivors in the Democratic Republic of the Congo and analyzed their blood for biological activity against the Ebola virus. The researchers found antibodies reactive against the Ebola virus in the blood of all 14 patients. In four of the patients, the antibodies in the blood prevented live Ebola viruses from infecting human cells.
Rimoin, the director of the UCLA-DRC Health Research and Training Program, works with the Congolese government, researchers and clinicians to monitor the spread of diseases. Previous studies had looked at Ebola survivors 11 years after infection, but Rimoin said she was interested in understanding the effects of the disease over a longer timescale.
“It’s not totally surprising that we found antibodies after 40 years,” she said. “What is surprising is that these antibodies had the same neutralizing ability as someone who had contracted the disease recently.”
Nicole Hoff, the country director for the UCLA-DRC research program and a co-author of the study, said the researchers could not be certain why some survivors still had immunity to the virus. Hoff, an assistant adjunct professor of epidemiology, added the survivors might naturally have active immune systems, or constant exposure to insects and animals in their environment kept their immune systems activated against viruses such as Ebola.
Rimoin said another reason may be that they were constantly re-exposed to the virus, either from the environment or from leftover viruses hidden within their bodies.
Because most of the Ebola survivors in the study and many field workers in the Congo have antibodies against glycoproteins, which make up the outer shell of the Ebola virus, the researchers suggest using Ebola glycoproteins in vaccines may train the immune system to easily recognize and remember the Ebola virus.
“About 30 percent of the (Congolese) fieldworkers are immunized to glycoproteins,” Hoff said. “Ebola glycoproteins seem to be the most easily targeted by antibodies.”
Adva Gadoth, a doctoral student in epidemiology and a member of the UCLA-DRC research program, said there are no documented cases of Ebola survivors contracting the disease a second time. This result suggests that once individuals produce antibodies against Ebola, they may be immune to the disease for the rest of their lives.
Understanding the body’s long-term responses to Ebola is critical considering more recent and larger Ebola outbreaks, Rimoin said. From 2014 to 2016, more than 11,000 individuals in West Africa died from contracting the virus, according to the Centers for Disease Control and Prevention.
“What’s really interesting about this work are the public health implications,” Rimoin said. “Not only do these Ebola survivors have antibodies against Ebola, but the antibodies are just as reactive 40 years after infection as someone who’s been recently infected.”
Gadoth added the Congo area remains an important area for studying the emergence and spread of disease.
“The Congo basin is the disease basin of the world,” Gadoth said. “Many strange infectious diseases pop up there before they show up elsewhere in the world.”