Here's the mBio article by Dr. Michael Osterholm and colleagues that was mentioned earlier today by The Washington Post: Transmission of Ebola Viruses: What We Know and What We Do Not Know. Excerpt:
It is very likely that at least some degree of Ebola virus transmission currently occurs via infectious aerosols generated from the gastrointestinal tract, the respiratory tract, or medical procedures, although this has been difficult to definitively demonstrate or rule out, since those exposed to infectious aerosols also are most likely to be in close proximity to and in direct contact with an infected case.
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.
Despite the lack of supportive epidemiological data, a key additional question to ask is whether primary pulmonary infections and respiratory transmission of Ebola viruses could be a potential scenario for the future. A fair amount of evidence suggests that such transmission could be possible, even without dramatic evolution or genetic changes in Ebola viruses (although viral evolution over time could enhance this possibility).
First, Ebola viruses can be isolated from saliva, and viral particles have been identified in pulmonary alveoli on human autopsies, suggesting that infectious aerosols could be emitted from the respiratory tract.
Second, Ebola viruses can infect several cell types found in the respiratory tract, including macrophages and epithelial cells (77).
Third, cough can be a symptom of EVD, and coughing is known to generate aerosols, although prevalence of reported cough is variable in case series (ranging from “rare” to 49%) (2, 6, 78).
Fourth, animal studies indicate that EBOV can be transmitted through aerosols and that respiratory infection with pneumonitis can occur following this route of inoculation.
Fifth, experience with RESTV suggests that respiratory transmission of that species can occur between animals and possibly from animals to humans.
Finally, people can generate and emit aerosols with particles of various sizes, including fine particles, which could enter the lower respiratory tract and infect susceptible cells; Ebola virus is in the respirable range (800 to 1,000 nm).
If aerosols containing Ebola virus were to enter the lungs of uninfected individuals, it is possible that primary pulmonary infections could occur (as shown in animal studies), which could then result in active viral shedding from the respiratory tract, thus potentially setting up a cycle of ongoing respiratory transmission in humans (79), similar to what occurs during outbreaks of pneumonic plague.
Investigators of a nosocomial outbreak of Lassa fever virus, another African hemorrhagic fever virus that is usually spread via contact with rodents (especially rodent urine), postulated that transmission may have occurred through the respiratory route (80, 81). Similarly, investigators of a nosocomial cluster of Crimean-Congo hemorrhagic fever, a vector-borne infection that occurs in Eastern Europe and Africa, identified probable aerosol transmission due to aerosol-generating medical procedures (82).
Experts in bioterrorism have long been concerned that hemorrhagic fever viruses, particularly filoviruses (Ebola virus and Marburg virus), could be used as potential agents of bioterrorism, with an aerosol being the most likely form of dissemination (83, 84). This concern has been grounded in uncertainty concerning the potential for aerosol transmission of such viruses. A strain of Marburg virus was weaponized by the Soviet Union, highlighting this risk (58).