The very large size of the Ebola virus makes it difficult to be transmitted by airborne means.
In many announcements and publications the US Centers for Disease Control (CDC) has stated that the Ebola virus is not transmitted by airborne means. According to the CDC there are no known cases of airborne transmission of the Ebola virus between humans. One must come into contact with fluids from an infected individual showing signs of illness. Then the virus in those fluids needs to have a pathway inside the body such as a cut or touching of the eyes, nose or mouth to infect someone. However, the debate persists on the issue of whether or not the Ebola virus can be transmitted by airborne means. As it turns out there are some physical characteristics of the Ebola virus which makes it very unlikely that it will be passed on through the air.
A major point to consider is that the Ebola virus is very large with an average size 0.9 microns. This is many times larger than other viruses such as influenza which is around 0.085 microns. The vast majority of viruses are in the 0.02 um to 0.3 um range.
Viruses do not “live” on their own. In fact, most scientists believe that the do not “live” at all. They must attach to cells to mulitply. A useful analogy is that the cell is like a computer while the virus is software.
Viruses need great numbers to overcome the human immune system. Individually, a virus is “stupid.” But when billions of the virus particles are exposed to human cells, a small percentage may make it through cell defense mechanisms and transmit disease.
Ebola is a terrible disease but does not appear to be easily transmissible. Consider the hundreds of people who were exposed in Dallas without contracting the disease.
But what happens when someone with the Ebola virus sneezes? Could the disease be transmitted by the large droplets in the sneeze? Particles of 10 microns or more settle out of the air very quickly. Visible particles start at about 10 microns. This means that all of the visible particles in a typical sneeze would settle within a few feet of the “sneezer.” In addition, unlike influenza, Ebola does not appear to be a respiratory disease. It attacks the internal organs such as the liver and kidneys but not the lungs. It is certainly possible that an individual infected with the Ebola virus would sneeze, but this is not a typical symptom.
Particles are also emitted by infected individuals by laughing, talking, coughing and exhaling. These are generally smaller particles. Particles of 5 microns and below can stay in the air for up to 20 minutes while particles below 1 micron act almost like gasses. But given the large size of the Ebola virus, what are the chances that these fine and ultrafine partices would be able to transmit the disease?
Since the Ebola virus is almost 1 micron by itself and it must be attached to a “host,” the chances for the Ebola virus to exist in sub-micron size particles is very low. Here is another critical point to consider. A 5 micron particle contains about 125 cubic microns while one drop of fluid (5mm in diameter) contains about 65,000,000,000 cubic microns. To put this in perspective, let’s assume that the same percentage of Ebola virus would be in a 5 micron size particle as the 5 millimeter diameter drop. In recent tests of a “simulated sneeze” the peak number of 5 micron particles 6 feet from the source was 1,800 particles per cubic foot. If we assume that an entire space was filled with 5 micron particles at this high level, it would take a building of 36,000 square feet (with 8 foot ceilings) to equal the amount of Ebola virus in one drop of fluid.
So when you consider whether or not the Ebola virus is a candidate for airborne transmission, the answer is possibly yes within a few feet of the infected individual. However, the odds favor transmission by fluid by a large margin – maybe a million to one.
This leads us to have serious questions about the claims of marketers of air filters, UV lights or other HVAC air cleaning devices when they say their products are effective on the Ebola virus. Frankly, it comes across as opportunistic selling at its worst.