Introduction to How Ebola Works
Malaria. Not a good thing, right? And when a patient named Mabalo sought treatment for his high fever back in 1976, that's what everyone assumed he had. He was, after all, living in the country then known as Zaire, a place well-known for high rates of malaria infections. So a nurse treated him for it with an injection of quinine and sent him on his way. Since she was low on supplies, she kept the needle she used to inject Mabalo for other patients.
Less than a month later, Mabalo died. As was customary in his region, his female friends and relatives performed a ritual burial procedure on his remains, removing all food and waste from his body with their bare hands.
Fast-forward a few weeks: Eighteen of the friends and family who had helped with this ritual had also died, and the hospital that had used the dirty needle was flooded with patients showing similar symptoms to Mabalo.
Malaria is bad, but not this bad. Doctors and scientists studying patient samples from this outbreak and a similar one occurring simultaneously in Sudan quickly realized they were dealing with something never before seen – the Ebola virus. All in all, 91 percent of the 358 people infected in Zaire died, and 53 percent of the 284 infected in Sudan succumbed to the disease [source: Smith].
Since 1976, the disease has popped up more than 20 times, mostly in Africa. And it's not showing signs of stopping. If anything, it's getting worse, spreading beyond its main hub of central Africa and showing its ugly face as far as Europe and the United States as of November 2014.
Just how ugly of a face? The fatality numbers speak to that. But we also have the ruthless efficiency with which this virus can kill – as quickly as within six days of showing symptoms. And those symptoms are far from pleasant – fever and achiness to start, leading to rash, bloody diarrhea, vomiting, and in many cases, massive internal and external bleeding.
That's arguably not even the worst part. Decades after discovering this monster, we still don't know that much about it. While we know how it gets transmitted between humans, scientists are only starting to make guesses on where it might come from and how we can prevent it.
Meet the Filovirus Family
Ebola is a beast of a virus, an evil villain disguised as a worm-like particle that invades your cells with no regard for life. And Ebola isn't just one evil villain; it's a whole family of five, with a not-too-distant cousin that sometimes visits, the Marburg virus (see sidebar). Beware any family that moves on to your block with the last name "Filovirus."
But unless you live in central or west Africa, you aren't that likely to come across the filoviruses. That's where four of these Ebola types originated. There's 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 as far as we know, it's not deadly to humans.
Like all families, the filovirus family members look like each other. Same eyes, same red hair ... well, not really. We're talking about something here that's only about one-sixth as long as a human hair is wide. 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: Smith].
Of course, the biggest likeness among the filoviruses is that they all kill their victims very similarly.
How Ebola Operates
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 compiled a handful of facts.
- The Ebola virus is most closely related to the viruses that cause measles and mumps, the paramyxovirus family.
- The genetic information stored in the RNA codes for only seven proteins (the molecules in the cell do most of the work in the organism), as compared to about 20,000 for humans.
- One of these proteins is suspected to be the superpower of the villainous Ebola: glycoprotein. One version of this protein binds to host cells, so the virus can enter and replicate, and the other version is released from infected cells and may play a role in suppressing the immune system.
- The virus is pretty impartial and will infect a wide range of cell types in our bodies, but early on, Ebola typically invades cells associated with our immune systems, namely monocytes, macrophages and dendritic cells. After that early infection, it travels to the lymph nodes, spleen and liver through the blood.
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, we can start to develop treatment for the disease and vaccines. But this is easier said than done. I mean ... would you want to be doing research on this disease? 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. Getting ahold of the virus can be challenging, too. Unless there's an outbreak, scientists don't really know how to find Ebola. Where it lives while it's not wreaking havoc is still a mystery. We'll give you our best guesses next.
Spacesuits on EarthBecause we need to learn about diseases like Ebola, a system has been set up for scientists to study disease-causing organisms. The organisms are all classified under one of four biological safety levels (BSLs), with one being the least scary to four being assigned to agents that can cause life-threatening disease and may be airborne. As you may have guessed, Ebola is a BSL-4 agent. In order for scientists to work with this virus, they must work in spacesuits with respirators and get decontaminated before entering and leaving these BSL-4 labs. Only about a dozen of these labs currently exist in the United States.
Ebola Symptoms
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 2-21 days (typically 4-10), 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 6-16 days after the onset of symptoms. Generally that death is not a result of the hemorrhaging, but from multi-organ failure or shock.
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.
Other Hemorrhagic FeversWhile Ebola is the best-known and most deadly of hemorrhagic fevers, it's by far not the most common out there. A small handful exist, including some well-known diseases such as dengue fever and yellow fever. These hemorrhagic fevers are largely found in Africa and South America, and the viruses are known to be carried by ticks, mosquitoes and rodents. Fatality rates vary with death rates as low as 1 percent (Rift Valley fever), all the way up to 70 percent (Crimean-Congo Hemorrhagic Fever) [source: Smith].
Ebola Plays Hide and Seek
Ebola first surfaced in 1976, popped up a few times over the next three years, and then virtually disappeared from existence for the next 15 years. But there's no way the virus really disappeared; it had to be hiding somewhere. Where it hid then and continues to hide between outbreaks is a mystery.
What we know: Ebola is a classic 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 to animals like mosquitoes, bats and birds. They have even tested out plants.
So why has it been so hard to find the reservoir species? Well, with the virus hiding for long stretches, there's a good possibility that the master Ebola hoarder is a rare species and hard to find. So scientists have looked. And looked. They've infected a ton of animals and then checked to see if they've survived or looked for antibodies against Ebola. This has been a decades-long quest and still there is no definitive reservoir species.
Recent tests have pointed to fruit bats as the most likely carriers of the disease, but scientists still are unsure how the virus transmits 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.
Ebola Breaks Out
Despite all the fear around Ebola, not that many humans have actually died from the disease, relative to other known diseases. Since 1976, in the 25 outbreaks that have 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) [sources: World Health Organization], CDC.
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 (60-90 percent for Zaire and 40-70 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 Zaire Ebola 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) and even going beyond Africa into the United States and Spain. Scientists are guessing that if, in fact, the virus is linked to bats, changes in climate could be causing differences in migration patterns of these bats, leading to the spread of Ebola beyond its origin of central Africa.
The two other African Ebola varieties, Ivory Coast and Bundibugyo, have only been observed three times with fairly low fatality rates. And finally, the fifth family member, the Reston type, seems to be most fatal to nonhuman primates. This particular strain also found its way into the U.S. (it's actually named after a fairly tame suburb of Washington, D.C.) in 1989 when an Ebola outbreak erupted from a primate research facility. Workers at the facility were thoroughly screened for symptoms and signs of the virus. Thankfully, this turned out to be the one type of filovirus that doesn't worm its way into humans.
(The CDC has a map of Ebola outbreaks in Africa if you're interested.)
The Spread of Ebola
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 before 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. So stay away from consuming or doing autopsies on those guys too.
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 3-6 days for a patient who has been stuck with a needle versus 5-9 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].
Monkey OutbreakFall 1989: A shipment of 100 wild "crab-eater monkeys" from the Philippines arrived at an animal quarantine facility in Reston, Virginia, belonging to Hazelton Research Products. Over the next few months, a third of the monkeys had died, and to contain the virus that scientists determined to be a new strand of Ebola, they euthanized all the animals. A new shipment of monkeys in January led to similar results, but this time several humans were also exposed to the virus, including a technician who had gotten cut accidentally with a bloody scalpel. Upon analysis of these infected people, scientists learned that although they had been exposed, the humans easily developed antibodies toward the virus -- making this strand of Ebola the only known filovirus to not produce any symptoms in humans.
Steering Clear of Ebola
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, the best ways to protect yourself from the virus are:
- Don't go into the forest or caves. Since bats are suspected to be the reservoirs of the virus, it's just best to stay away from places where they are present.
- Try to control yourself from messing around with dead animals. No hunting, no autopsies, no taxidermy, no consuming of bushmeat. Especially not on monkeys and apes.
These two guidelines should help you from becoming the index patient in an outbreak. And to keep yourself from becoming a later victim in an outbreak, don’t come into direct contact with anyone who is showing symptoms of the disease since the virus is passed through contact with bodily fluids. This means using protective measures in health care situations (like gloves and goggles), never reusing dirty needles and staying away from participating in any burial rituals on Ebola victims.
Other than those protective measures, there isn't much else to be done to avoid Ebola. There have been some observations that apes have a higher susceptibility and mortality from Ebola at the end of the rainy season and start of the dry one. It's thought that seasonal changes cause stresses in animal populations as they come in closer contact looking for food, perhaps becoming more aggressive. So if the resting place of Ebola is in an animal, times of season change may not be the best time for you to schedule an African safari, especially if your safari includes hunting near caves.
If you are unlucky enough to contract the disease, go to the next page to learn more about how doctors and scientists detect it and what they are doing to try to thwart the virus from its path of destruction.
Detection, Treatment and Prevention of Ebola
Detection of Ebola can be a little tricky before an outbreak is known to have started. The early symptoms are often confused with other diseases, and by the time the illness is identified as Ebola, it can be too late to do anything. 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. These tests, like the ELISA (enzyme-linked immunosorbant assay) test, generally look for antibodies for the Ebola virus instead of looking directly for the virus itself.
Aside from difficulties in bringing the test equipment into remote African villages, these tests are problematic in that a key feature of filoviruses is that they suppress immune systems. So even if someone is infected with Ebola, the virus may have suppressed the immune system enough that they were not able to develop any antibodies against it. Another powerful test known as PCR, or polymerase chain reaction, identifies the virus directly, which is a plus. However, not only is it hard to take into the field, it's also very sensitive to contamination, and the middle of an outbreak doesn't tend to be the most contaminant-free location.
At this point, though, even if a patient is identified to be infected with Ebola, there really isn't much that can be done other than basic interventions (IV fluids, maintaining oxygen and blood pressure, and treating other infections as they occur). With this type of care, patients have been known to recover from the virus. Some experimental treatment options such as a drug called ZMapp have been developed, but these products are still in the experimental phase and have not been totally approved by the U.S. Food and Drug Administration for safety or effectiveness. The best we can do once we know that an Ebola virus is on the loose in a region is to educate health care workers and members of the community in the outbreak on how best to reduce transmission.
So that may lead you to ask, Why wait until an outbreak to do something to fight Ebola? Can we get a vaccine? Good question! Because the number of victims has been so low (relative to other diseases) and the outbreaks tend to happen in remote parts of the world where it is difficult to administer vaccines, there hasn't been much industrial support for creating one. However, the spread of the 2014 outbreak outside of Africa is changing attitudes toward the need for a vaccine. This, along with the threat to the great ape population and the fear that Ebola could be used in an act of bioterrorism has spurred scientists to start working on one. So far, scientists have discovered a vaccine that protects monkeys from the ruthless virus, but that hasn't translated into a vaccine for humans just yet. Promising findings do suggest that a suitable vaccine for humans can be developed and early stages of human testing are underway.
For more resources on Ebola, check out the next page.