How climate change, development may be hastening Ebola’s spread

When it comes to Ebola, we’ve been worried about the wrong thing, says a renowned virologist.

Media speculation that the virus could mutate to become airborne and be transmitted as easily as the flu caused such public concern that the World Health Organization in the fall felt compelled to issue a statement saying there is no evidence or anticipation that that will happen.

But more than cause panic, the rumors distracted attention from what we really should be worried about: all that we don’t know about the Ebola virus’s natural reservoir and its ecosystem, said Dr. Leslie Lobel, a virologist from Ben-Gurion University’s National Institute for Biotechnology.

“The three key questions to ask about an infectious disease outbreak are: ‘What is the reservoir? What is the route of transmission? And what is the ecosystem?’ To control viruses, we need to control all these things. The only answer that’s known is route of transmission,” he told a packed auditorium of scientists Tuesday at Fred Hutchinson Cancer Research Center. In addition to cancer, Fred Hutch is a leader in infectious disease research.

A natural reservoir refers to an animal that can harbor the virus without being killed by it, allowing it to live and multiply between outbreaks in humans. The African fruit bat, for example, is the natural reservoir for the Marburg virus, which causes a similar severe hemorrhagic fever. Many believe that fruit bats, which, according to Lobel are “all over the place” in Africa and hard to control, are also the reservoir for the Ebola virus. But Lobel pointed out that has not been proven.

A virus’s ecosystem means the environment in which its reservoir resides — which is why identifying the correct reservoir is so important — as well as the way people live and interact with that environment. Africa is “a virus-rich ecosystem,” Lobel said, in part because people live closely with animals and with each other, allowing viruses and other pathogens to pass among them. He has been studying the immune response of Ebola survivors in Uganda for more than a decade in an effort to develop a vaccine.

Countries in West Africa continue to battle the most severe outbreak of Ebola since the virus was discovered in 1976. According to the most recent WHO report, more than 17,800 people have been infected and more than 6,300 have died since the outbreak was declared in March, numbers that WHO acknowledges are vastly underestimated.

WHO Director General Margaret Chan said Wednesday that Liberia is showing progress in containing the epidemic and that cases in Guinea and Sierra Leone were less severe than a few months ago, but still high. Ebola is spread by direct contact with blood or bodily fluids of a person who is sick with Ebola or with contaminated objects such as bedding or syringes.  

Climate change, globalization and rapid development of previously undeveloped regions have all made Africa more vulnerable to devastating diseases. All disrupt the habitats of virus hosts and bring them and humans closer together.

“Whatever the ecosystem of Ebola is, it’s being encroached in a big way,” Lobel said. “With globalization and global warming, we’re going to continually be encroaching on ecosystems. It’s going to be a challenge moving forward.”

Lobel has seen these changes firsthand as he’s made repeated visits to Africa over 13 years to study survivors of a 2000-2001 outbreak of the Sudan strain of the Ebola virus in northern Uganda. (There are five known strains of Ebola; the Zaire strain is behind the ongoing outbreak in West Africa.) As with all research projects, his began with a question: Does the immune system produce antibodies to Ebola that persist over time, and if so, what can be learned from this?

To answer this question, he tracked down survivors and visited them regularly to draw blood. Many of them live in mud huts deep in the bush, which Lobel points out are easier to find now that everyone has cell phones and can be tracked by GPS coordinates. As important as the meticulous record-keeping has been the relationships he has developed with his subjects.

“We follow them and give them feedback on what we’ve learned,” he said. “Many of them are pariahs, shunned [because they had had Ebola]. We view them as blessed because they survived.”

The answer to his question about whether the antibodies to Ebola linger over time in survivors turned out to be yes. By studying people who lived through the virus, his team has been able to identify those with the best immune response and isolate antibodies from them. His lab is working on an antibody “cocktail” that will be tested in animals soon and could be available for humans as a preventive vaccine and a therapeutic in three to five years.

But even if a vaccine or treatment is successful, more will be needed to control this and future outbreaks, Lobel told Fred Hutch researchers.

“Obviously, people are more interested now in therapeutics and vaccines and everything else, which is what gives us jobs,” he said. “But in reality, we really need to disrupt the ecosystem to gain greater control. This is the way most influenza is controlled in the world. It’s at the level of the veterinary community, controlling outbreaks in chickens and swine.”