Ebola's Deadly Jump From Animal to Animal

Ebola may be present in more animals than previously thought, according to researchers studying the deadly virus, which has already been detected in chimpanzees, gorillas, fruit bats, monkeys, antelopes, porcupines, rodents, dogs, pigs and humans.

Watch "Ebola: Are We Next?" on Thursday, Sep. 18, starting at 9/8c on both Discovery Channel and Discovery Fit & Health.

Humans and other primates appear to be particularly susceptible to at least certain strains of the virus. During the present outbreak ravaging Guinea, Sierra Leone and Liberia, Ebola has killed 670 people so far and infected more than 1,000.

"The close evolutionary relationship between humans, chimpanzees and gorillas makes their immune systems very similar," Peter Walsh, a primate expert at the University of Cambridge, told Discovery News.

According to the World Health Organization, humans can get Ebola through close contact with the blood, secretions, organs or other bodily fluids of infected animals (including other humans), so people who consume or otherwise handle certain bush meat are at particular risk. Eating infected non-human primates doesn't tell the whole story, however.

There is growing consensus that fruit bats are ground zero for the illness that kills up to 90 percent of humans who become infected. Most of the infected bats appear to come from the following three species: Hypsignathus monstrosus, Epomops franqueti and Myonycteris torquata.

"In general, Ebola researchers think that the natural host of Ebola virus are fruit bats, and that the virus is transmitted to non-human primates and then to humans through the bush meat trade," Purdue University's David Sanders, one of the world's leading experts on zoonotic diseases, told Discovery News.

He added, "It is possible that there is direct transmission from fruit bats to humans."

Certain cultures in Africa do consume bat meat, such that Guinea earlier this year ordered a ban on consumption of these flying mammals in an effort to halt the epidemic's spread.

As for how non-human primates might become infected, they often feast on fruits that the bats eat. They can also kill and eat bats, or scavenge meat from infected carcasses.

Then the question remains: How did bats get the virus?

Sanders and his team found that the way Ebola infects human cells is nearly identical -- both structurally and biochemically -- to the way that similar viruses enter bird cells. This suggests that the proteins of the virus had a comparatively recent ancestor.

"It is therefore possible that Ebola was at one time associated with a bird host and may even be so today," Sanders said, adding that the bird must hail from Central Africa. That is where the virus was first detected in 1976 and where outbreaks usually occur.

Even plants and insects could have played some role in the evolution of the virus, as Thomas Monath of the Harvard School of Public Health has proposed. Monath postulated that a nonpathogenic virus in insects and/or plants might have mutated, giving rise to Ebola in bats.

Blaming humans, bats, chimps or birds for the illness does not then take into account its full possible scope within the ecosystem. That, the present unprecedented epidemic, the potential for bioterrorism, and the fact that no vaccine is available for clinical use have scientists around the world paying greater attention to Ebola and to the animals it can infect.

Sanders and his colleagues continue to study birds and their possible role in Ebola's evolution and transmission. They are also attempting to determine what other animals might be added to the already long list of species that the virus and related viruses could impact.

A fruit bat clutching some oranges.

In Madagascar, about 500 people every year contract the plague.