Ebola: Contagious vs Infectious

Read my earlier Ebola primer.

As the CDC treats the nation’s first two Ebola cases there are a lot of questions and concerns about the disease in America—Could it become an epidemic here? How contagious is it? How is it caught?

Although my medical specialty is cardiothoracic surgery, I have spent a good deal of time working on global health issues in Africa and elsewhere, and I have been in close contact with the CDC over the past week. I thought it might be useful to highlight some of the features of Ebola that make it more—and less—dangerous.

As a viral disease, Ebola follows a fairly predictable timeline.

Incubation: the time between when a person is exposed to the virus, and when symptoms start. In Ebola, that incubation period can be between 2 and about 21 days. During that time, the patient does not feel sick and research suggests that they are not contagious. (see doi:  10.1016/j.phrp.2011.04.001) There’s been concern about infected travelers spreading Ebola to other parts of the world after traveling from West Africa. That is certainly possible with a long incubation period.

Onset of Symptoms: However, once an infected person starts to feel sick, they are quickly seriously ill. There is sudden onset of fever, intense weakness, muscle pain, headache and sore throat. This is followed by vomiting, diarrhea, rash, impaired kidney and liver function.

Unlike a cold, when you could be spreading the virus and not really feel that unwell, Ebola patients know that they are sick. This is actually a good thing, because sick patients are easy to identify, isolate, and treat. Other diseases still need to be ruled out—malaria, typhoid fever, cholera—but it’s clear that the patient has a severe illness.

Transmission: Here is perhaps the scariest part. How do you get it? How did Dr. Brantly get it? How is the virus spreading between people?

Some diseases are infectious, but not contagious. Lyme Disease or Rocky Mountain Spotted Fever are transmitted from ticks to humans but cannot be spread from human to human.

Contagious diseases can be spread from person to person, but not all equally well. Chicken pox, small pox, and measles, for example, are airborne spread—meaning the virus spreads very well with each exhale. These diseases are highly contagious.

Ebola, on the other hand, is only spread through direct contact with the bodily fluids of infected patients—blood, semen, sweat, urine and other secretions. And then, that fluid needs an easy entry into the body: a shared needle, an open cut, an exposed mucous membrane. It could possibly be spread through a cough or a sneeze, but that would require a fairly large drop of mucous to be coughed into another person’s face and get into their mouth or nose or eye.

For healthcare workers in West Africa, this could be possible. With limited supplies, perhaps there is a tear in a glove, or there aren’t enough goggles to go around, or bedding is reused because there isn’t an adequate way to clean it.

If patients are being cared for at home—either because they are too far away from a medical facility, or there’s some cultural distrust of foreign aid workers—caregivers in close physical contact with sick loved ones would have no medical or cleaning supplies. There are also vast cultural issues that influence the virus’ spread, and I’ll touch on those soon.

But with supplies, knowledge, and fully-equipped medical centers, these circumstances would be much less likely to happen. For these reasons, the Centers for Disease Control (CDC) is not concerned about an outbreak in the United States.

The situation is certainly serious—and will continue to be very serious in West Africa. But although we don’t know everything about how this virus behaves and changes, we do have quite a bit of useful knowledge about how to keep it contained, and how to keep our healthcare workers at home and abroad safe.