We all need to STOP and think about Ebola with the science of transmission in our minds eye.
With 21 day quarantines all the rage these days ( it reminds me of the post 9|11 security theater that we still deal with at airports and big buildings ), I thought it important to discuss how the Ebola virus actually spreads. When you understand how difficult it is, and what it requires, perhaps you will share this page with a few friends so we can move away from hysteria and focus on helping the people in West Africa tamp this thing out.
First let’s all acknowledge Ebola is a horrible disease. Traditionally it has a mortality rate in the 50 percent or more range. Ironically, thanks to an increase in both wealth and mobility coupled with social customs and political factors, things are making the spread more difficult to control in western Africa than in places like the US or even Nigeria.
In epidemiology there is a statistic called the R naught which helps us understand how contagious a disease is. This number tells us how many people, on average, a sick patient will infect. For example, a person with measles infects 18 additional people on average (in an unvaccinated population – thanks Jenny McCarthy!). Each patient with Ebola only infects 1.5 to 2.
Ok, so how does the Ebola virus move from one person into another?
The Ebola virus, it requires direct contact. This means you have to get it not just on your intact skin, which can be a pretty effective barrier, but you have to get it onto one of your mucous membranes (nose, eyes, mouth, etc.), or in a cut.
Ebola can’t stay alive outside the body for a long time if it gets dried out or exposed to sunlight. Dry is not good for Ebola and sunlight is not good for Ebola. It’s one of the easiest to kill of all pathogens. If you spray it with rubbing alcohol or a regular disinfectant like Lysol, it will die. Sufficient sunlight will kill it. So that’s the good news.
Ebola is not spread through the air like measles or chickenpox. However, if you are standing nearby when someone coughs, sneezes, or vomits, you could get droplets of these bodily fluids into your mouth, nose, or eyes. This is what is considered direct contact. It should be pointed out that is the most conservative view of possible transmission mode, most of the Ebola virus spread which has occurred in West Africa seems to be related to much more direct methods. In West Africa, people are becoming ill after contact with blood or vomit, urine or feces.
Once the virus enters the body, it targets several types of immune cells that represent your first line of defense against invasion. It infects your dendritic cells, which normally display signals of an infection on their surfaces to activate T lymphocytes—the white blood cells that could destroy other infected cells before the virus replicates further. With defective dendritic cells failing to give the right alarm, the T cells don’t respond to your infection, and neither do your antibodies that depend on them for activation. From there, Ebola can start replicating immediately and very quickly.
Ebola, like many other viruses, works in part by inhibiting interferon—a molecule that cells use to hinder further viral reproduction. In a new study published in Cell Host & Microbe, researchers found that one of Ebola’s proteins, called VP24, binds to and blocks a transport protein on the surface of immune cells that plays an important role in the interferon pathway.
Interestingly, your lymphocytes themselves don’t become infected with the virus, but a series of other factors—a lack of stimulation from some cells and toxic signals from others—prevent them from putting up a fight.
So, as you can clearly see, because of the Ebola viruses’ method of transmission and infection, we can be very reassured that a person with Ebola can’t really spread the disease until they are pretty sick. You can be exposed to influenza and pass it on to your family within two or three days—before you develop symptoms. With Ebola that takes about two weeks and symptoms MUST be present for a day or two before it’s highly contagious.
If you stop and think about it, the very first patient to become symptomatic in the United States, Thomas Eric Duncan, stayed with relatives prior to developing symptoms. Even after he spiked a fever, he was unable to infect those around him even though they were all sharing a small apartment. The people Mr. Duncan did infect, were two nurses who were not adequately covered when dealing with his blood, vomit, urine and feces.
The bottom line is that you are not going to catch Ebola from a person who has even a fever but is otherwise symptom free. So, the policy of beginning a quarantine of an individual who has (a) been exposed to the Ebola virus; and (b) spiked a temperature of >= 100.4 BEFORE they have ANY other symptoms is THE BEST POLICY. Everything else, like these silly 21 day quarantines for symptom free people, is just an attempt to pacify all those people who cannot, for whatever reason, grok the science.