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EBOLA GOING AIRBORNE?

Posted on by Laurie Garrett

Few viruses conjur the kind of fear generated by an outbreak of Ebola, a microbe most commonly found in central Africa that causes people’s capillaries and blood vessels to leak, leading to massive hemorrhaging.  I wrote about the first-recognized Ebola epidemic  in Yambuku, Zaire in 1976; Richard Preston described the monkey-Ebola scare in Reston VA; and I covered the 1995 outbreak in Kikwit, Zaire. In every case it was apparent that Ebola conjured a special kind of terror, largely because the afflicted patients ooze blood from every orifice and exhibit deranged behavior as blood fills their brains. Moreover, mortality rates have run as high as 90 percent.

The one comfort has been discovery that person-to-person transmission is largely due to unclean medical conditions or burial procedures, both of which can be easily corrected. In other words, if people were not directly exposed to the blood and fluids of an Ebola patient, or needles and medical equipment contaminated with such fluids, they rarely became infected. This “comforting” finding has diminished concern that Ebola could spread to pandemic scale, and demonstrated clear interventions for stopping outbreaks.

But now researchers in Spain offer disturbing findings that seem to prove that the virus has found a way to spread via airbone transmission among bats. If this finding holds up under continued scrutiny we could be witnessing real-time evolution of one of the world’s most dreaded microbes. The discovery underscores three key principles of emerging diseases work:

  1. the need for surveillance not only of humans, but perhaps even more importantly wild animals; 
  2. recognition new microbes can “fly” on the wings of those they infect; 
  3. that Nature is constantly pushing the genetic envelope.

When Ebola was first discovered in 1976 the chain of transmission hit a deadend with a small clinic in Zaire that was run by Belgian Catholic nuns. It seemed their Patient Zero was a hunter that staggered into the facility and died. The nuns subsequently carried out their normal medical procedures, using three syringes over and over again – essentially injecting the virus into their patients. Scientists were unable at the time to determine what animal the hunter may have contacted, causing his original infection. The Kikwit outbreak in 1995 originated with a man who spent time deep in the rainforest bruning wood to make charcoal. It was clear the man acquired his infection thru contact with a wild animal, and evidence seemed to point to fruit bats.

Subsequent Ebola outbreaks have similarly originated at the fringes of still-wild rain forest areas, either thru contact with ailing apes or monkeys, or general hunting. It is now known that all primates (chimps, gorillas, monkeys) can become infected with Ebola and suffer the same horrible diseases as is seen in humans. But they are not the reservoir of the virus – the species in which the virus inhabits normally, causing little or no illness to the host.

Ebola is part of the family of viruses called Filoviruses, which includes Marburg Disease. Evidence now points to fruit bats as the reservoirs for all of the Ebola strains, as well as its Filovirus cousins. In almost all cases the Filovirus is harmless to the reservoir bat species.

But no always, and this is where things now get interesting, and worrisome.

In 2005 researchers reporting finding bats inside caves in Spain that were ailing. By 2010 it was clear that an epidemic was unfolding, and spreading rapidly, among cave bats in Portugal, France and Spain, especially in the Spanish Cueva del Lloviu region. Entire bat colonies were obliterated within days. Whatever was killing them seemed to be highly contagious.

A large multi-institute Spanish/USA team led by Gustavo Palacios of the Mailman School of Public Health at Columbia University in New York isolated a new virus from one of the dead bats. Using techniques pioneered by Columbia’s Dr. Ian Lipkin the Palacios team isolated a new virus, which they named Lloviu after the cave region, and acronymned LLOV. Two different bat species were sick and dying in the caves – all infected with the mysterious LLOV.  Genetic analysis indicates the LLOV are on the same evolutionary tree as Ebola and Marburg, but descended from a different common ancestor virus, probably more than 150,000 years ago.

Why has this virus suddenly appeared, where did it come from, and how did it manage to spread so rapidly?

Normal Filoviruses infect bats harmlessly, and are shed thru the animals’ feces, infecting primates or other mammals (including a reported pig) that get in contact with the contaminated feces. That mode of exposure is very haphazard, and exceedingly rare.

While the Palacios team cannot yet answer the questions, “Where did this come from?” or “Why did this suddenly appear?” the rapid spread among bats seems clear: the virus is airborne, in two ways. It is spreading between bats without the fecal route, perhaps through saliva droplets. And it is spread between colonies of bats over vast distances via flying, infected animals that migrate across southern Europe.

Now the worry points boil down to a simple but troubling list:

  • Can ailing bats spread the virus to non-bat mammals, such as pigs, horses and humans?
  • Will the LLOV prove as lethal to other species of mammals as it seems to be for the European bats?
  • Has its sudden appearance been the result of a genetic change – a tiny evolutionary step – that has given the virus new capabilities?

The Palacios team notes that genetic differences between LLOV and Ebola or Marburg include some factors controlling the inate immune response in bats – the crucial first steps in recognizing and responding to infection.

This bears close watch.