How Ebola Works

Ebola belongs to a virus family called Filoviridae, aka filoviruses, which also includes the Marburg virus (see sidebar).

But unless you live in central or west Africa (or travel there), you aren't that likely to come across the filoviruses. That's where four of these Ebola species originated. There are the Zaire and Sudan strains, which are the most deadly for humans, as well as the Bundibugyo and Tai Forest varieties, which have only been seen a few times. The fifth type, Reston, is the only non-African variety, having originated in the Philippines, and it's the only one that doesn't cause severe disease in humans [source: CDC].

Like all families, the filovirus family members look like each other. The worm-like shape of a filovirus is often described as "hooked," like a shepherd's crook. They all get their genetic material from RNA, instead of DNA the way we do. And their genetic information is not terribly complicated. While humans have 3 billion base pairs in their DNA, the molecules that make up the RNA of a filovirus only number about 19,000 [source: VanMeter and Hubert, ViPR].

Of course, the biggest likeness among the filoviruses is that they all kill their victims very similarly.

Each strain of the Ebola virus operates pretty similarly. In fact, they work in standard virus fashion (see How Viruses Work for details), hanging around in some sort of reservoir or host and waiting for a vulnerable cell to come along so they can infect it. And while scientists don't know all the details of how Ebola works in the body, they have learned some of these details.

Just like other viruses, once Ebola infects our cells, it triggers the release of a bunch of different types of chemicals that cause the terrible symptoms associated with the disease (more on those later).

As we learn more about how Ebola works in our bodies, scientists can start to develop treatment for the disease and vaccines. But the dangers of working with this virus make learning more about it quite challenging. Scientists have to be well protected and work in Biosafety Level 4 laboratories (see sidebar), but even with that, they still risk their lives to gain an understanding of Ebola.

And even getting samples of the virus to study has been difficult at times, too, because regulators and transport companies were reluctant to allow them to be shipped [source: Steenhuysen].

Where it lives while it's not wreaking havoc is still a mystery. We'll give you our best guesses next.

If you've seen the movie "Outbreak," you probably associate viruses like Ebola with massive bleeding coming out of all orifices of the body. While this isn't completely untrue, the actual symptoms of Ebola are not usually that macabre.

When Ebola enters a human it hangs out seemingly harmless for two to 21 days (typically four to 10), until the symptoms start appearing. First come the fever, chill, headache, muscle and joint aches, and tiredness. At this point, unless there is a known outbreak, the disease can often be confused for many other types of illnesses. And given the most common location of infection is in Africa, malaria is often the first disease that health care workers diagnose.

But then the disease quickly takes a turn for the worse. Patients start complaining of bloody diarrhea, severe sore throat, jaundice, vomiting and loss of appetite. When symptoms have been present for five days, about half of Ebola victims will develop a rash on their trunk and shoulders [sources: Groseth, Smith]. And after this it can get really ugly.

While massive bleeding is actually rare, one of the prominent components of this infection is that patients start to hemorrhage. Their blood starts to clot all throughout their bodies and that quickly exhausts the supply of proteins that handle clots. So that means when tissue damage occurs in other parts of the body, those proteins aren't available to do their clotting work, resulting in uncontrolled bleeding. Now this happens for only about 50 percent of patients, and the uncontrolled bleeding is mostly internal, in the gastrointestinal tract [source: Feldmann]. So while massive bleeding may occur from other parts of the body, it's pretty uncommon.

All of this trauma very quickly adds up to a bad outcome for many patients. For fatal cases, death occurs six to 16 days after the onset of symptoms. Generally that death is not a result of the hemorrhaging, but from multi-organ failure or shock [source: CDC].

Ebola acts quickly, but causes a lot of pain and suffering in its victims during that time. Since treatment options are often unavailable in outbreak areas (more on that later), it's safest to just stay away from the virus. Read on to learn what we know about how it started and how it spreads.

Ebola first surfaced in 1976, popped up in isolated places over the next several years, and then virtually disappeared until a 1995 outbreak in the Congo that killed 250 people. Five years later, an outbreak in Uganda killed 224 more people. Since then, it's continued to return on an irregular basis, with a 2014 outbreak in the Congo taking 49 lives [source: CDC].

What we know: Ebola seems to be a zoonotic disease, meaning that it occurs naturally in animals but can be transmitted to humans. So that means a likely resting place, or reservoir, for Ebola could be an animal that becomes the source of direct transmission. But here's the tricky part: Since Ebola lies in silence for long periods, animals that get sick from the disease, like primates, are probably not the reservoirs. If a monkey were the reservoir, that would mean that the virus would be able to hang out in the monkey for long stretches of time without making the monkey sick. And we know that monkeys are super susceptible to the disease, so scientists have had to look elsewhere [sources: Rewar, etal.].

Researchers have injected the Ebola virus into a variety of animals — from pigeons to lizards — and then checked to see if they've survived or looked for antibodies against Ebola [source: Cowart].

Recent research has pointed to fruit bats as likely reservoirs of Ebola, though not all scientists agree. But it's still unclear just how the virus would make the jump from the bats to humans and nonhuman primates. We only know that some of these African bats can support the virus replicating in their bodies without getting sick and that bats have been associated with known index cases (the first human infected in an outbreak) in past outbreaks [sources: Kupferschmidt, Cowart, Vogel].

Despite all the fear around Ebola, not that many humans have actually died from the disease, relative to other known diseases. Between 2014 and 2016, in the 25 outbreaks that occurred, about 16,000 cases of humans infected with Ebola have been reported and about 6,500 of those cases have ended in death. (Note: More than 80 percent of the Ebola cases reported are attributed to the 2014 outbreak in West Africa.) [source: World Health Organization].

As we mentioned, Ebola is actually a family of five virus types. The two most deadly to humans are the Zaire and Sudan types. Not only do these have the highest fatality rates (60 to 90 percent for Zaire and 40 to 70 percent for Sudan), they've also appeared the most in the known outbreaks that have occurred [source: Feldmann].

After the initial appearances of both of these strands in 1976, the viruses hid for awhile. But when the Ebola family reappeared, it came back with a vengeance. Since the mid-'90s, both of these Ebola types have wreaked havoc on Africa every few years. Most of these outbreaks have been contained to central Africa quite close to the equator in countries like the Democratic Republic of Congo, Gabon and Uganda. In March 2014, however, the first outbreak of the Zaire strand was seen outside of this region in the western African country of Guinea, quickly spreading to nearby countries (Liberia, Sierra Leone, Mali, Senegal and Nigeria).

That year, a visitor from west Africa to the U.S. turned out to have Ebola, and two health care workers in Dallas who treated him tested positive for the disease. They both recovered. In addition, a medical aid worker who had volunteered in Guinea also was hospitalized in New York City, and was confirmed to have the disease. He also recovered [source: CDC].

Scientists worry that Ebola outbreaks have the potential to spread more rapidly, due to climate change. The latter's effect on the trees in Africa, which bats depend upon for food, may cause an increase in bat reproduction, or else compel the animals to roam to new areas. In addition, as droughts affect agricultural areas and force humans to go into the forest for food, they may be exposed more often to bats carrying the Ebola virus [source: Barnato].

Given that we really don't know where Ebola lives most of the time, it's hard to get a good sense of how the very first person in an outbreak (index case) gets infected. For past outbreaks, the index cases are largely unknown, but a few have been identified as having been in places where bats have been present, or the victims have been known to have interacted with dead animals.

Beyond the unknowns of how the first person got infected, we do know how the virus is transmitted otherwise. Human-to-human transmission occurs as a result of close contact with blood, secretions or tissues from patients where the virus can travel to a new victim through mucosal surfaces or breaks in the skin. So the African burial rituals we mentioned earlier where family members clean out the waste from dead bodies? Yeah, that's a bad idea when your loved one has died from Ebola. We also are aware of cases of human-to-animal contact resulting in infection. As far as we've seen, those known animals are gorillas, chimps and a type of antelope called a duiker.

Thankfully, we haven't learned of any cases where the virus passes to humans via aerosol contact — or through the air. In the Ebola outbreak on monkeys in the U.S., the Reston Ebola virus was able to pass through the air to infect many of the monkeys in the research facility (see sidebar). A 2012 study conducted on pigs and monkeys with the Zaire strain also showed transmission of the disease without direct contact, but as far as we know, this airborne transmission method is not linked at all to humans [source: Weingarti].

One of the easiest transmission methods to control is the passing of the virus through dirty needles. Reuse of needles at health care facilities has massively impacted the numbers of infected people in past outbreaks, but with knowledge of this as a transmission route for the virus, health care workers can take extra precautions to keep used needles from being used again.

Depending on how the virus gets transmitted, the outcome of how Ebola affects a patient can change. For example, incubation periods for the Zaire type of Ebola is three to six days for a patient who has been stuck with a needle versus five to nine days for a patient who has had contact exposure. And in the first known outbreak in 1976, 100 percent of the patients who had been infected via needle-stick succumbed to the disease, whereas about 80 percent of the cases due to contact were fatal [source: Feldmann].

While some cases have been reported elsewhere, the most dangerous forms of Ebola are largely found in central and western Africa. So you're probably safe if you don't venture into those parts of the world very frequently. But if you do, here are some recommended precautions.

Keep reading to learn more about how doctors and scientists detect Ebola and what they are doing to try to thwart the virus from its path of destruction.

Detection of Ebola has been a difficult problem, especially before an outbreak is known to have started. The early symptoms are often confused with other diseases. It can take up to three days after the onset of symptoms for the virus to reach levels that can be detected [source: CDC].

The most accurate tests for Ebola are those that use specialized equipment that is hard to take into the remote locations where the virus is most prevalent.

In 2017, however, researchers reported a breakthrough in Ebola diagnosis — a test using a device called the Quantitative, Rapid Identification (QuRapID) platform, which freezes blood cells to spill their contents and mixes them with a dye that helps to spot the virus. As described in a 2017 article in The Conversation, the entire process reportedly takes 70 minutes to provide a result [source: Moschos].

Once a patient has been diagnosed with Ebola, there are some measures health care workers can take that will improve the person's chance of survival. The standard treatment involves providing fluids and electrolytes intravenously, as well as oxygen therapy and medication to support blood pressure and reduce vomiting and diarrhea. While people who recover from Ebola develop antibodies to the disease, it's not known whether those make them immune to catching it again. Survivors may suffer lasting health problems, such as difficulties with their joints and vision problems [source: CDC].

But a vaccine recently developed by pharmaceutical maker Merck may at last provide a way to stop Ebola. The vaccine was first tested in late 2015, toward the end of an Ebola outbreak in west Africa, and of the 7,500 people who received it, not a single one developed the disease. In May 2018, with a new outbreak raging in the Congo, National Public Radio reported that thousands of doses had been shipped there, to be used in a vaccination effort coordinated by the World Health Organization [source: Aizenman].