I’ve read that article and others several times—how do you think I am able to speak of virus transmissibility in bodily fluids?
The only column that matters as far as transmissibility in Table 1 of that article is labeled “Virus culture positive, no. (% sample type tested).” The RT-PCR test can only tell you that viral RNA was present in the sample, but cannot tell anything about the condition of the virus. In a similar manner, you can use RT-PCR to test for and find cow RNA in a steak, but that doesn’t mean you have a living cow on your dinner plate.
Culturing the virus is the only way to know if a sample is infectious. I notice that many of the fluids listed in that table that contained viral RNA did not, in fact, contain active virus. The single saliva sample that had live virus in it probably contained blood. From the number of saliva samples that contained RNA but not culturable virus, it would seem that saliva inactivates the virus (which is not surprising; we have many antiviral and antibiotic molecules in our mucous secretions). The only two fluids I saw that concern me are the breast milk and semen. They contained live virus during the acute phase of the illness, and continued to harbor live virus for a period of time after symptoms subsided. Not in this study, but in another, live virus was cultured from a semen sample collected 82 days after symptoms appeared. *That* is very concerning.
Assessment of the Risk of Ebola Virus Transmission from Bodily Fluids and Fomites (From Discussion)
There was a significant discrepancy between the results of virus culture and RT-PCR testing in our study, with many more frequent positive results from RT-PCR. Possible explanations for this finding include virus degradation from breaks in the cold chain during sample collection, storage, and shipping; the greater sensitivity of RT-PCR relative to culture; and, in the case of the saliva specimens, possible virus inactivation by salivary enzymes. The less-than-ideal storage conditions of the specimens in the isolation ward immediately after acquisition and the fact that even the nasal blood from 1 patient was culture negative suggest that some virus degradation indeed occurred. Nevertheless, we cannot exclude the possibility of a true absence of viable virus in the original samples. We hope to be able to repeat this study in the future with better maintenance of the cold chain to resolve this question.
Given that the nasal blood of an infected individual in the midst of clinical symptoms came up negative on culture, this study has a significant problem that the authors noted. Use of this study to make claims regarding transmission without the accompanying qualifier isn't particularly good practice IMO, especially when used to claim that a particular vector is impossible/improbable.
I think the RT-PCR test results are the significant portion of this specific study given the issues surrounding the sample handling.
In a previous post (number 2118) you wrote:
In order for Ebola to become airborne, it would have to 1) infect cells in the upper respiratory system, in the bronchia and possibly alveoli, and 2) be resistant to destruction by drying.
Ebola infects dendritic cells, which are numerous in the respiratory tract. Additionally, the virus has demonstrated very wide tropism in animal models and human samples. Please provide a source for the claim that other respiratory cells are not currently subject to infection and "must" be infected in order for airborne (medical definition) transmission to occur. As far as I am aware, the various cell types of the human respiratory tract are not exempt from Ebola infection.
UMN CIDRAP:COMMENTARY: Health workers need optimal respiratory protection for Ebola
Medical and infection control professionals have relied for years on a paradigm for aerosol transmission of infectious diseases based on very outmoded research and an overly simplistic interpretation of the data. In the 1940s and 50s, William F. Wells and other "aerobiologists" employed now significantly out-of-date sampling methods (eg, settling plates) and very blunt analytic approaches (eg, cell culturing) to understand the movement of bacterial aerosols in healthcare and other settings. Their work, though groundbreaking at the time, provides a very incomplete picture.
Early aerobiologists were not able to measure small particles near an infectious person and thus assumed such particles existed only far from the source. They concluded that organisms capable of aerosol transmission (termed "airborne") can only do so at around 3 feet or more from the source. Because they thought that only larger particles would be present near the source, they believed people would be exposed only via large "droplets" on their face, eyes, or nose.
Modern research, using more sensitive instruments and analytic methods, has shown that aerosols emitted from the respiratory tract contain a wide distribution of particle sizes—including many that are small enough to be inhaled.5,6 Thus, both small and large particles will be present near an infectious person.
(snip)
Being at first skeptical that Ebola virus could be an aerosol-transmissible disease, we are now persuaded by a review of experimental and epidemiologic data that this might be an important feature of disease transmission, particularly in healthcare settings.
What do we know about Ebola transmission?
(snip)
On the basis of epidemiologic evidence, it has been presumed that Ebola viruses are transmitted by contaminated hands in contact with the mouth or eyes or broken skin or by splashes or sprays of body fluids into these areas. Ebola viruses appear to be capable of initiating infection in a variety of human cell types, but the primary portal or portals of entry into susceptible hosts have not been identified.
(snip)
Ebola virus, on the other hand, is a broader-acting and more non-specific pathogen that can impede the proper functioning of macrophages and dendritic cells—immune response cells located throughout the epithelium.15,16 Epithelial tissues are found throughout the body, including in the respiratory tract. Ebola prevents these cells from carrying out their antiviral functions but does not interfere with the initial inflammatory response, which attracts additional cells to the infection site. The latter contribute to further dissemination of the virus and similar adverse consequences far beyond the initial infection site.
The potential for transmission via inhalation of aerosols, therefore, cannot be ruled out by the observed risk factors or our knowledge of the infection process. Many body fluids, such as vomit, diarrhea, blood, and saliva, are capable of creating inhalable aerosol particles in the immediate vicinity of an infected person. Cough was identified among some cases in a 1995 outbreak in Kikwit, Democratic Republic of the Congo,11 and coughs are known to emit viruses in respirable particles.17 The act of vomiting produces an aerosol and has been implicated in airborne transmission of gastrointestinal viruses.18,19 Regarding diarrhea, even when contained by toilets, toilet flushing emits a pathogen-laden aerosol that disperses in the air.20-22
Experimental work has shown that Marburg and Ebola viruses can be isolated from sera and tissue culture medium at room temperature for up to 46 days, but at room temperature no virus was recovered from glass, metal, or plastic surfaces.23 Aerosolized (1-3 mcm) Marburg, Ebola, and Reston viruses, at 50% to 55% relative humidity and 72°F, had biological decay rates of 3.04%, 3.06%. and 1.55% per minute, respectively. These rates indicate that 99% loss in aerosol infectivity would occur in 93, 104, and 162 minutes, respectively.23
In still air, 3-mcm particles can take up to an hour to settle. With air currents, these and smaller particles can be transported considerable distances before they are deposited on a surface.
(snip)
Direct injection and exposure via a skin break or mucous membranes are the most efficient ways for Ebola to transmit. It may be that inhalation is a less efficient route of transmission for Ebola and other filoviruses, as lung involvement has not been reported in all non-human primate studies of Ebola aerosol infectivity.27 However, the respiratory and gastrointestinal systems are not complete barriers to Ebola virus. Experimental studies have demonstrated that it is possible to infect non-human primates and other mammals with filovirus aerosols.25-27
Altogether, these epidemiologic and experimental data offer enough evidence to suggest that Ebola and other filoviruses may be opportunistic with respect to aerosol transmission.28 That is, other routes of entry may be more important and probable, but, given the right conditions, it is possible that transmission could also occur via aerosols.