Monday, February 23, 2015

Limited airborne transmission of Ebola is ‘very likely,’ new analysis says/ WaPo

As discussed in this blog last October and November, Ebola transmission by air is likely, but also likely not a major form of spread. The WaPo comments on an academic piece written by several experts in the field:
... As evidence, the research notes that Ebola virus has been found on the outside of face masks worn by health workers caring for victims of the disease. It also points out that the virus has been passed between animals via respiration. And the authors say that Ebola can infect certain cells of the respiratory tract, including epithelial cells, which line body cavities, and macrophages, a type of white blood cell that consumes pathogens.
The paper notes that breathing, sneezing, coughing and talking can release droplets of fluid from the respiratory tract that travel short distances and most likely cause infection by settling on a mucous membrane. Those actions also release smaller airborne particles capable of suspension in mid-air that can be inhaled by others. Technically, both qualify as aerosols, the paper says.
The debate has centered on whether Ebola can be transmitted via those smaller particles. William Schaffner, an infectious disease specialist at Vanderbilt Medical Center who did not take part in the study, praised it for raising the issues "in a thoughtful fashion" and predicted it would be "very, very widely read."
He said he could imagine the possibility of respiratory transmission of Ebola from close-in contact, perhaps a distance of three or four feet. Even so, Schaffner said, it would be rare; as the study points out, it has never been demonstrated in humans.
The common mode of transmission--contact with body fluids--"those are the highways of transmission," Schaffner said. "Could respiratory transmission occur? Yes. But it's probably a byway, a little trail in the forest."
Asked why many more people who were near Ebola victims had not become infected, Osterholm said the Ebola virus may be much less contagious than other diseases spread by respiration, such as measles. He likened it to tuberculosis, which is more difficult to contract this way.
In an e-mail, Kobinger said that "we hope that this review will stimulate interest and motivate more support and more scientists to join in and help address gaps in our knowledge on transmission of Ebola (and other filoviruses). Important policies and biosafety regulations must be evidence-based, not [by] using opinions and beliefs as guiding principles."
The review itself points out that "to date, investigators have not identified respiratory spread (either via large droplets or small-particle aerosols) of Ebola viruses among humans. This could be because such transmission does not occur or because such transmission has not been recognized, since the number of studies that have carefully examined transmission patterns is small."

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