Deadly Virus Hunters Discover Ebola, Marburg Source In Fruit Bats
After a five-year search in the jungles of Africa, an international team of virus hunters has identified a fruit bat that may be the natural host for both hemorrhage-causing diseases. Also, the viruses are more widespread than previously thought, according to their research, which was accepted this week for publication in the open-access journal BioMed Central.
The study, based on blood tests on more than 2,000 bats in Gabon and the Republic of Congo, will help scientists solve a mystery that has confounded them for more than 30 years: which species harbor Ebola and Marburg without getting sick. The answer may explain how the viruses persist in the environment and point to ways humans can avoid a disease that causes fatal bleeding and organ failure in at least half of cases.
“Very eminent scientists have been searching for decades to find the source,” said John Mackenzie, a Melbourne-based virologist who assists the World Health Organization in its response to outbreaks. “Until you know what it is, you cant piece together the epidemiology or begin to think about managing the risks to both humans and wildlife.”
Marburg hemorrhagic fever was recognized in 1967, when outbreaks occurred in laboratories in Marburg and Frankfurt, Germany, and in the Serbian capital, Belgrade. Cases were traced to African green monkeys imported for research and polio vaccine production. Nine years later, a closely related virus was found to have sparked a deadly outbreak near the Ebola River in the Democratic Republic of Congo, formerly known as Zaire.
Caves and Mines
Disease trackers have tested everything from snakes to guinea pigs in the search for an animal reservoir and have been repeatedly led back to caves, mines and bats.
A 2005 study published in the journal Nature found evidence of symptomless Ebola infection in three species of fruit bat in West Africa, indicating that these animals may be the ones carrying the virus.
The latest study is the first to show that Ebola and Marburg circulate simultaneously in bat populations in one country. While several human Ebola outbreaks have occurred in Gabon, no cases of Marburg have been reported there, the authors said. The presence of Marburg virus in the West African nation represents a “potential and previously unrecognized threat to humans,” they said.
Bats Blood
“These findings provide much stronger evidence for a reservoir in bats,” Xavier Pourrut, a virologist at Gabons International Center for Medical Research in Franceville and the studys lead author, said in a telephone interview. “The next step is to understand how the viruses circulate in bat populations over time.”
Pourrut and collaborators from the Special Pathogens Branch of the Centers for Disease Control and Prevention in Atlanta and Frances Institute for Development Research looked for evidence of previous Ebola and Marburg infection in the blood samples of 2,147 bats from at least nine species.
Of all the bats sampled in significant numbers, only specimens of the cave-roosting Egyptian fruit bat, or Rousettus aegyptiacus, were found to harbor antibodies against both Marburg and Ebola, the authors wrote, “suggesting that this species may be a natural host of both viruses.”
Eating Apes
The Egyptian rousette, with a doglike face and ears, is found along the Nile River in Egypt and across Sub-Saharan Africa. While some groups may occasionally roost outside in trees, the bats of this species prefer to inhabit caves, mines and tombs, and feast on fruit trees at night.
These preferences give it a stronger link with the circulation of Marburg than Ebola, a virus more frequently found in rain forests, said Pierre Formenty, leader of the emerging and dangerous pathogens team at the WHO in Geneva.
While some outbreaks in humans have been directly linked to contact with bats, most of them probably began from contact with infected apes, chimpanzees and other primates that are sometimes eaten in Africa. These animals, in turn, probably got the virus by eating fruit contaminated with saliva or other bodily fluids from bats, according to Pourrut.
Once a human is infected, there is no cure for Ebola or Marburg. After an incubation period of about a week, victims rapidly develop high fever, diarrhea, vomiting, respiratory disorders and hemorrhaging. Death can ensue within a few days. About a quarter of Marburg cases are fatal, whereas case fatality rates range from 50 to 80 percent with Ebola in Africa.
Infected Saliva