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What is Ebola?

Ebola electron microscopeWhat is Ebola?

Ebola disease is a life-threatening illness caused by the Ebola virus. In December 2013, a 2-year-old toddler died in a rural village in Guinea, sparking the largest Ebola outbreak the world has ever known (Baize et al., 2014). The outbreak primarily involves three countries in Western Africa: Guinea, Liberia, and Sierra Leone (although there have been additional cases/deaths in other countries). As of early November 2014, there have been over 13,000 cases and almost 5,000 deaths, although experts believe that these numbers could be 250% greater as many patients never seek medical assistance. This outbreak is larger than all previous Ebola outbreaks combined, and the Center for Disease Control (CDC) predicts the disease could spread to other West African countries, infecting over 1 million people by January 2015 (Meltzer et al., 2014)!

Ebola map of disease spread
The Ebola outbreak is serious because:

  • Previous outbreaks were generally limited to rural villages, but the 2014 outbreak has moved into more densely-populated areas where there is increased opportunity for human-to-human transmission. 
  • There is currently no vaccine or specific medication for Ebola, and the threat of the disease spreading can cause widespread panic around the world.

How does virus replication work?

Many viruses follow the same sequence of events to replicate themselves. In regards to the Ebola virus:

  1. The Ebola virus slips inside of a human immune cell (e.g. macrophage).
  2. The virus turns the cell into a virus factory, assembling a clone army of the Ebola virus. Meanwhile, chemicals that impair the blood’s ability to clot (a condition called thrombocytopenia) are released into the bloodstream. This is what causes the unexplained bleeding in patients.
  3. The cell eventually explodes releasing Ebola viruses that infect nearby healthy cells. The exploding cell sends out chemical signals which seep into the bloodstream and alert the immune  system about the infection. The immune system’s response to the invading virus is what causes the patient’s flu-like symptoms (e.g. fever).

Ebola pathophysiology with virus replication

What are the symptoms of Ebola and how is it diagnosed?

It takes between 2 to 21 days (most commonly: 8-10 days) for the Ebola virus to replicate enough to cause symptoms, and initially Ebola can look like a case of a bad flu. To help make things clear, the CDC has listed two key criteria that a patient must meet to raise suspicion of Ebola:

Ebola clinical diagnostic criteria

Ebola can cause many other symptoms including weakness, poor appetite, rash, red eyes, hiccups, cough, chest pain, and difficulty breathing/swallowing. On their own, these symptoms do not indicate that a person has Ebola, since they could be caused by a number of things.

If health care professionals suspect Ebola, they’ll order the following blood tests to confirm the diagnosis:

  • Polymerase Chain Reaction (PCR): Looks for viral RNA
  • Enzyme-Linked ImmunoSorbent Assay (ELISA): Looks for anti-viral antibodies

How does Ebola spread?

Ebola is spread when the bodily fluids of a sick patient get inside of a healthy person. These bodily fluids include blood, vomit, feces, urine, saliva, sweat, breast milk, and semen. The virus can survive in bodily fluids that come in contact with surfaces like floors, walls, and handrails for about 24 hours although the chance of infection after a few hours drops significantly (Center for Disease Control, 2014c). Family, friends, and healthcare professionals all care for patients and are at higher risk of coming into contact with the virus. These folks and anyone else at risk (e.g. funeral directors and lab workers) should protect themselves with personal protective equipment, and remove it in the correct order: gloves, then face shield, then gown, and finally mask!

Graph of total cases and death for Ebola

Ebola can also spread through contact with body fluids of infected bats and primates, placing individuals who work with or in close proximity to these animals at a higher risk of contracting the disease.

Once a patient recovers and is symptom-free, he or she is no longer able to transmit the virus. The one exception is transmission through semen, which can transmit Ebola for up to 3 months after infection. Ebola patients are encouraged to abstain from sex during this time. Ebola survivors can go on to have a normal life and are immune to the virus for up to 10 years.

To be clear, Ebola does not spread through the air, through water, or through food, so you can breathe, drink, and eat without worry!

How likely are you to get Ebola?

It’s really useful to know how many people are likely to get infected from a single contagious patient (assuming that nobody gets vaccinated). A number called R₀ (pronounced: R-“not”) allows scientists to rank how contagious a disease is:

  • R₀ of 0 means that nobody will catch the infection
  • R₀ of 1 means that 1 new person will catch the infection
  • R₀ of 5 means that 5 new people will catch the infection, and so on...

In some diseases, a single patient can spread the disease for days (e.g. Ebola) and in others, for decades (e.g. HIV). It turns out that Ebola has an R₀ of 2, which means that a single patient will transmit the virus to an average of 2 other people (unless we intervene). Compare this with one of the most contagious viruses around - Measles, which can travel in the air and spread to an average of 18 people!

R-nought for various diseases including Ebola
Sources: Center for Disease Control & World Health Organization, n.d.; Meltzer et al., 2014; Mills, Robins, & Lipsitch, 2014

How can you treat Ebola?

Unfortunately there is no direct treatment for Ebola (no vaccines or medications) yet. Instead, health care workers provide supportive care, which focuses on keeping the patient alive during the illness while his/her body fights the disease. Supportive care includes:

  • Keeping the patient well hydrated with intravenous fluids
  • Maintaining the patient’s blood pressure
  • Helping the patient breathe, if needed
  • Treating other infections or ailments that come up

Typically people who are likely to survive begin to recover between 6 and 11 days after symptoms initially began. Older patients and those that have more serious symptoms such as bleeding early on in the course of the disease typically die within 6 to 16 days after symptoms initially began (Center for Disease Control, 2014b).

Consider the following:

Why are some countries more affected by Ebola than others? The answer comes down to having an effective public health system. There is a race taking place. On one side, the virus is quickly moving from one person to another. On the other side, the public health team is trying to find and isolate everyone with Ebola so that the virus can’t spread. Speed matters on both sides, and if the public health team can move quicker than the virus, then transmission ends. This requires good surveillance and contact tracing.

  • Surveillance: Some countries have excellent public health systems, and healthcare providers at clinics/hospitals call public health departments about any patient who has an unusual illness or death. Other countries have many rural populations that cannot visit major health facilities because they’re too far away. In these cases community health workers are often sent out, but they sometimes can’t get to every community. As a result, people may get sick and die without the public health team ever learning about it, and the disease can spread far and wide without anyone noticing.
  • Contact tracing: Once a patient is diagnosed with Ebola, the patient is isolated to prevent further chance of spreading the disease. Public health teams then make a list of everyone the patient may have spread the disease to while the patient had symptoms and monitors them for symptoms for 21 days. If one of those people gets sick, the public health team will isolate them and make another list of everyone this new patient may have spread the disease to while this new patient had symptoms. Ideally there should be no one on the list if the public health team works fast enough!