How does the Ebola virus spread?

Emily Landon ebola

Soon after the first diagnosis of Ebola Virus Disease in the United States, bodily fluids became a socially acceptable and near-ubiquitous topic of conversation. A New York Times article graphically described a scene, now distressingly common, in a West African clinic:

"Nurses, some not wearing gloves and others in street clothes, clustered by the door as pools of the patients' bodily fluids spread to the threshold. In the next ward, a 4-year-old girl lay on the floor in urine, motionless, bleeding from her mouth, her eyes open. A corpse lay in the corner - a young woman, legs akimbo, who had died overnight. A small child stood on a cot watching as the team took the body away, stepping around a little boy lying immobile next to black buckets of vomit. They sprayed the body, and the little girl on the floor, with chlorine as they left."

Last week, we spoke with hospital epidemiologist Emily Landon, MD, about the ways this disease is transmitted and how that plays into deliberations about how to handle any possible case that present to a U.S. hospital.

What does the phrase bodily fluids really mean?

When it comes to Ebola, contagious bodily fluids include blood, vomit, urine, stool and, to a lesser extent, tears and saliva-all of those, plus semen, where the virus can still be present three months after the patient gets better. That's not a source that we typically focus on if we find ourselves doing contact tracing for a disease like this, but it could become important to keep in mind.

How does the virus move from one person into another?

For this virus, it requires direct contact. That means you have to get it not just on your intact skin, which can be a pretty effective barrier, but it has to get onto one of your mucous membranes (nose, eyes, mouth, etc.), or a cut. The virus has to get inside your body. However, you can touch infected body fluids and then touch your mouth or nose or eyes. That would be a risk too.

Is it spread by coughing or sneezing?

It is not generally spread through the air like measles or chickenpox, but people standing nearby when someone coughs, sneezes, or vomits could get droplets into their mouth, nose, or eyes. We consider that direct contact. That can spread the disease theoretically but studies have not identified that as an important risk factor. Most of the disease spread that has occurred in West Africa seems to be related to much more direct methods, contact with blood or vomit, urine or feces.

How long is the virus contagious?

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.

How quickly does it spread?

It's a horrible disease, with a mortality rate in the 50 percent or more range, but social and political factors make spread more difficult to control in western Africa than in places like the US or even Nigeria. In epidemiology we use a statistic called the R naught to help 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). Each patient with Ebola only infects 1.5 to 2. We can also be reassured because a person with Ebola can't spread the disease until they feel pretty sick. You can be exposed to influenza and pass it on to your family within two of three days-before you develop symptoms. With Ebola that takes about two weeks and symptoms are present for a day or two before it's highly contagious.

It's a welcome change to hear good news about Ebola. But how long does that take, for it to dry out or for sunlight to kill it? If somebody with Ebola throws up on the street, how long will it stay moist enough to cause disease?

This is not good news. Say somebody vomits in the street. You step on it. The ground is wet. A little vomit gets stuck in the treads of your shoes. Sunshine doesn't go there. You walk home, take you shoes off and set them in a dark moist place. You don't wash your hands. Or maybe you do, but you move the shoes later and don't wash your hands. Then you touch your eyes or nose. We all do that habitually without thinking about it. You could get Ebola. It's very unlikely to happen that way, but it is possible. Please notice that there were a lot of "ifs" in that scenario. Little things like washing hands and cleaning the things you stepped in off your shoes would interrupt transmission.

"Most of us have a pretty good idea of whose bodily fluids we've come in contact with." -- Dr. Emily Landon, during an interview with Al-Jazeera

How much Ebola does it take to make you sick?

It's unpredictable. We don't really know just yet. It may depend on your immune system. What we do know is the longer the patient has been infected, the sicker they get, the more virus-laden they become, which means there is more virus is in their vomit, urine, blood, whatever. By the time they are vomiting uncontrollably, which along with severe diarrhea is common with this disease, these people are very sick and more likely to spread the infection to unprotected individuals.

Where does Ebola live in a patient? Is it partial to certain tissues?

For all intents and purposes it's in blood, in all secretions, but it doesn't come out through the skin. No one has isolated whole virus particles in sweat at this time. The virus disrupts the usual clotting and bleeding patterns. This strain has not caused as much hemorrhaging as some previous strains. That's why they are calling Ebola virus disease (EVD) rather than its other ominous name, Ebola hemorrhagic fever.

If it's so hard to get, why is it spreading so rapidly in West Africa?

This is a war torn region with limited medical care, profoundly damaged public health and safety systems, a pervasive sense of political mistrust and a culture of frequent personal contact. This is why the funerals of Ebola victims are problematic. Someone who has died from the virus will have a very high viral load. Those who participate in the ritual washing of an Ebola victim and then touch their face, or eat, could get the virus. Remember that clean water for washing hands is a luxury that we take for granted and, with Ebola, it makes a big difference. There's also the issue of public mistrust of the government and health workers that keeps some patients from seeking medical care. And there aren't enough quarantine beds to care for everyone who is sick so some people are turned away from treatment centers and sent back home to spread the virus to others.

What does the word Ebola mean? It just sounds ominous. Where did that name come from?

Ebola virus disease first appeared in 1976 in two simultaneous outbreaks, one of them in the Democratic Republic of Congo, in a village near the Ebola River, which forms part of the northern boundary of that country. The disease takes its name from the river.

Should a patient turn up here, how would we handle them?

Everyone who comes to UCM and complains of or has fever or symptoms consistent with Ebola will be asked about travel. If they have both symptoms and travel, they are placed in the nearest isolation room and the infection control team is contacted. We do additional screening to see if the patient really does have risk of Ebola. While this is being sorted out, any care the patient needs is provided by healthcare workers wearing recommended personal protective equipment. Outside of our quarantine area, that means a fluid resistant surgical gown, shoe and leg covers, a mask, and a face shield.

How would we handle their bodily fluids and waste?

We've been giving that a lot of thought. It has been an issue elsewhere. The key, until we know more, seems to be a combination of extreme caution and high redundancy. It starts with a complex procedure for simply removing it from the patient's room. Waste goes into a garbage can which is then wrapped in a garbage bag. Then, that bag gets bagged and sealed. Then it's sprayed down with disinfectant. This gets put in another bag. That gets sprayed down with disinfectant and placed into a transport container and taken away to the basement where it gets heated in a large pressure cooker. Then it can be removed safely. There's a similar process for spills. The designated rooms will have a five-gallon bucket of bleach or other disinfectant, as well as industrial-size kitchen tongs and beach towels. First, the towels are soaked in the disinfectant. Then we would use the tongs to pick them up and place them onto the spill, in such a way that the spill gets completely soaked with disinfectant. Then everything gets carried by tongs to a nearby garbage can, where it can be contained. Then you clean the floor again with disinfectant. You don't spray a spill. That could release droplets into the air.

Priority one must be keeping the clinical staff safe. How foolproof is protective gear?

Once you realize that a patient may have Ebola, every hospital has people who know what to do. Hospitals see a lot of contagious patients. We are working with experienced professional caregivers, who volunteer for this task. We provide extra training, to make those issues top-of-mind. We go over how to put on the gear and how to take it off. People most often make mistakes when they take it off. Sometimes it requires patience and meticulous care to remove contaminated protective gear safely. We have the fancy Tyvek suits but they protect the staff only after they've been taught how to put it on and take it off. For this reason, we use more familiar protective equipment that is easier to remove in the emergency rooms and clinics (see above). This is less comfortable for the clinician but just as safe. Because of research projects on campus, we have a fabulous biosafety team with a ton of experience training people. There are little things you wouldn't think of. For example, sleeve covers over the Tyvek suit. These are easy to put on and take off. You take them off first, before removing the suit.

After all this meticulous preparation, what do you worry about the most?

  I'm pretty comfortable with the logistics of taking care of a patient while protecting the staff. I worry about finding patients early enough, before they get really sick and pass the virus on to their family. I worry about the little glitches that have the potential to delay detecting an infected person, time that gives the virus a chance to spread. I worry that the people who make the first contact, in the clinics or in the emergency room, will forget to ask patients about fever and travel, or contact with people who have traveled. That is the weak point of every clinic, every hospital in America-identifying a patient at first interaction. I need everybody, our 1,400 nurses and 1,000 doctors, to know that if there is a fever, if a patient looks sick, you need to ask about travel. That's not the first thing on the mind of an orthopedic surgeon, for example. I'm an infectious disease doctor, so I'm going to ask, but not everyone thinks that way. Every time we don't do that, there's a risk. Getting everybody to do the same thing, hundreds or thousands of times a day, in a situation where it may seldom, if ever, have an impact is, as you know, difficult at best. We're hoping for and building in redundancies; if one caregiver forgets to act, the next person they meet with will. That's the number-one issue for hospitals. Once you identify a patient with Ebola, every hospital has sufficient capacity to take care of him or her and to protect their staff. Maybe not every hospital has stacks of the fancy Tyvek suits like university hospitals do, but they have sufficient knowledge and protective gear.

How does Ebola compare to the other causes of death in Africa?

  Below is a chart from the World Health Organization. It's a bit out of date already but it gives you a sense of scale. Keep in mind that this is for all of Africa. A similar chart for just Liberia, Sierra Leone and Guinea would-unless we get this outbreak under control pretty soon- have a different look. But so far (Oct. 7, 2014), Ebola deaths are still running in the same range as Lassa fever (another hemorrhagic fever virus), which causes, on average, 5,000 deaths a year in this region.


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John Easton
John Easton

John Easton is a senior science writer at UChicago Medicine.