Scientists Say Ebola’s Transmission Route Unlikely to Have ChangedWhile Ebola Constantly Mutates, It’s Unlikely The Virus Has Become Airborne
The Wall Street Journal
Gautam Naik Updated Oct. 16, 2014 4:17 p.m. ET
News that two nurses in Texas were infected with Ebola despite wearing protective gear has sparked fears that the virus may be changing in a way scientists don’t yet understand—by becoming airborne, for example.
While there is no doubt the virus is constantly altering its genetic makeup, scientists are confident Ebola hasn’t suddenly acquired the ability to be transmitted via air and is unlikely to do so.
“Ebola is more-or-less the same as it was in 1976,” when it was discovered, said Ian Jones, professor of virology at the University of Reading in the U.K. “Most viruses, once they’ve established a way of life, stick with it.” No human virus is known to have changed its mode of transmission. Viruses like yellow fever that are transmitted by mosquitoes, or HIV that is transmitted by body fluids, continue to be passed on in the same way.
Ebola’s transmission route hasn’t changed either. It is usually the result of close and direct physical contact with a patient’s infected body fluids, especially blood, feces and vomit. While the virus can also be transmitted indirectly—via contaminated surfaces and objects—that risk is low and it can be lowered further by disinfection procedures. Ebola can survive on dry surfaces, such as doorknobs, for several hours but is easily killed.
Viruses that store their genetic information in the form of the DNA chemical code, such as smallpox, typically don’t undergo a large number of mutations. By comparison, viruses based on the RNA chemical code, such as Ebola and HIV, are less stable. RNA is a molecule inside the cell thatamong other things, passes on genetic information. HIV’s high mutation rate is one reason why it is so hard to develop a vaccine for it.
So it wasn’t a surprise when a study published in the journal Science in August found the 2014 Ebola virus had undergone more than 300 genetic changes compared with the virus that caused earlier outbreaks in the region.
What did those changes amount to? Is Ebola changing in a way that allows its host to live a few weeks longer, so it could potentially infect even more people? Is it acquiring properties that could make it airborne?
The answer to those questions is no, researchers say. “There’s no evidence that a particular mutation is being selected,” said Dr. Jones. “We don’t see anything happening that’s changing the direction of the virus in one direction or another.”
For a germ to be airborne, it has to form a cloud of dried droplets that can survive for a long time suspended in the air. People at some distance from the original source can get infected when they walk through the cloud and inhale the droplets. This makes the germ a lot more transmittable. Measles and chickenpox are two airborne viruses. By contrast, a germ like Ebola gets passed on via larger, wet droplets, which results in a typically lower transmission rate.
Some studies have isolated the virus from the saliva of patients at a severe stage of the illness, which suggests Ebola could be spread via coughs or sneezes. In a Harvard School of Public Health poll published Wednesday, 85% of respondents said they believed someone could get Ebola if a symptomatic person sneezed or coughed at them.
But Ebola doesn’t usually cause coughing or sneezing, and neither of those functions equate to airborne transmission, according to the World Health Organization. In theory, it is possible for a victim to sneeze or cough out virus-laden heavy droplets that land on the mucus membranes or an open cut of another person nearby and cause infection—but such droplets couldn’t travel any great distance, as with a truly airborne virus.
The WHO says it doesn’t know of any research documenting this type of transmission. TIt is also quite firm about the possibility that Ebola might be passed from person-to-person via the air.his month it said: “Speculation that Ebola virus disease might mutate into a form that could easily spread among humans through the air is just that: speculation, unsubstantiated by any evidence.”
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