The Internet has been flooded of late with information (and significant misinformation) about Ebola. The most popular search term on Google is now “Ebola” (recently it was “Twerking”). But with all the information available, much of it offered up by non-scientists and armchair-experts, how does the average person sift the facts from what is essentially background noise?
Well, if we think like an Epidemiologist, we can sort it out fairly easily. As epidemiologists, we start at the beginning with the virus itself.
Ebola is one of the Filoviridae family of viruses, comprised of filamentous particles that encode their genome in the form of single-stranded negative-sense RNA. Viruses are tiny, and can be as small as 1/100th the size of even the smallest bacteria.
Ebola virus, like Marburg virus, is classified as a zoonotic disease; it is transferrable from non-human animals to humans. Zoonotic diseases include Rabies, Hanta virus, Anthrax, Lyme, Bubonic Plague, Toxoplasmosis, and dozens more. It is thought that Ebola first infected humans from a small fruit bat when humans pushed into undeveloped areas. A biting insect bites the bat, and then if that insect bites a human, the virus is transferred. The first step in epidemiological discovery is to identify the natural reservoir of the disease; the animal that carries the disease without showing it. Once you have identified the reservoir, you can take the initial steps to minimize contact with the organism. This is an issue because many communities in Ebola-prone areas consider the fruit that bats snack on to be a delicacy. This provides an easy transfer from host-to-host through the bat’s saliva.
The virus does not harm the bats, as they have evolved a defense against it. Not so for humans, or for many domestic and farm animals, that become reservoirs for the virus. The transfer of the virus from an infected person to an uninfected person occurs through contact with infected bodily fluids including blood, vomit, urine, and feces. The mortality rate of Ebola is between 40% and 90%; the current pandemic is at about 65%. This makes Ebola highly lethal. But exactly HOW does the virus make us ill?
Viruses can only influence a living organism by invading the cells. Viruses do not have the ability to replicate on their own; they are not actual living organisms but simple microscopic packets of DNA or RNA genes wrapped in a protein coating. Yet viruses can infect every living thing, from plants and animals, to the smallest bacterium. Because they lack the ability to replicate, they require a living cell to do the replicating. Infection can happen several ways: by air (think coughing, sneezing), through a vector (insects like mosquitoes that bite) and by direct transmission of body fluids (saliva, blood or semen).
Once the virus invades the living cell, it attempts to convert all of the cells energy to replicating new viruses. It is fruitful and multiplies. A lot. And with each new replication, the host cell produces more viral material than normal genetic material of the host. If the virus is allowed to replicate unstopped, the cell becomes packed with the virus genes until it pops from internal pressure, and the new viruses will leak into surrounding tissue and spread to nearby cells, beginning the process again. Simple math can demonstrate how bad this is using the geometric sequence, 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2038, etc. But hold on. Help is on the way. Well… maybe.
The human body does have the natural defenses against some viral infection. Our cells can initiate RNA interference when it detects the viruses RNA. When the cell starts to expel foreign matter, other cells that circulate the body called plasma cells, detect the invader and begin to manufacture Y-shape proteins called antibodies. These antibodies locate and attempt to neutralize foreign objects, including bacteria, viruses, and parasites. They do this by attaching to the invader and locating the antigen (a part of the invader virus or cell) and binds to it to prevent it from making more copies. The immune system also manufactures T-cells, which work to kill the virus, bacteria, or parasite by engulfing and dissolving it. T-cells also help other immune cells to survive ingesting invaders and those that produce antibodies. Most amazingly, T-cells are the backbone of immunity; they can remember an infection they encountered decades ago, making it very difficult for reinfection by the same invader; at the first signs of infection by a “known” invader the infection is rapidly dealt with, often before symptoms even appear.
Unfortunately for the organism, some viral infections, particularly novel ones, simply outperform the immune response. Evolutionarily speaking, viruses evolve significantly faster than the immune system, which gives them a great advantage in uninterrupted reproduction, particularly if it is a novel invader. Some viruses, HIV for example, survive and multiply by invading the very cells responsible for fighting infection, allowing for greater susceptibility to opportunistic infections like colds, influenza, and other minor infections by destroying the immune system from the inside out. Viruses are responsible for many diseases; colds, measles, chicken pox, HPV, herpes, rabies, SARS, influenza, and many others including Ebola.
Symptoms of infection.
When a virus, bacteria, fungus, or parasite infects your body, the immune system’s response is to cause inflammation. You’ve experienced this as a fever, muscle aches, headache, and an overabundance of mucus in your sinus cavities and lungs. Infection by a hemorrhagic virus (think hemorrhage) adds to this list the breakdown in tissues and organ systems your immune system goes into overdrive. Hemorrhagic viruses include five different “families” or subgroups including Arenaviridae (Lassa fever, Lujo virus, Argentine, Bolivian, Brazilian and Venezuelan hemorrhagic fevers), Bunyaviridae (Hantavirus, the Crimean-Congo hemorrhagic fever, Garissa virus and Ilesha virus, and Rift Valley fever, Filoviridae (Ebola virus and Marburg virus), Flaviviridae (Dengue, yellow fever, and tick-borne viral encephalitis). Similar to an HIV infection, Ebola and Marburg infect the immune system itself, the monocytes and macrophages. Your body is left with an inability to mount a defense when you first become infected. The virus replicates unchecked until the infection has grown so large that the rest of your immune system can’t help but notice. Then, the system goes into overdrive; in an effort to kill the virus, your body produces high fever followed by shock ( a lack of blood flow). Your tissues start to degrade and blood pressure drops; this is often followed by organ failure.
All viruses act quickly. The initial symptoms of Ebola (and many other viruses) are varied, and are often mistaken for malaria, typhoid fever, influenza or various bacterial infections, all far more common than Ebola. For this reason it may take several days for Ebola to be diagnosed, and only after secondary symptoms have begun (diarrhea, red eyes, vomiting blood, gastrointestinal bleeding, hemorrhaging from the nose and mouth, and bleeding in the brain, seizures and delirium). After the secondary symptoms appear, within a week to ten days patients either recover or die from multi-organ failure. Another factor that makes diagnosing Ebola difficult is that visible hemorrhaging presents in less than half of the patients infected. The bad news is that this latest outbreak caused by the Zaire strain causes the most severe symptoms.
Can’t we just cure this?
No. Viruses are virtually impossible to cure, although prevention is possible. The reasons for this are fairly straightforward and have to do with the basic structure of the virus. Because a virus cannot reproduce on it’s own, it requires the manufacturing abilities of living cells. They accomplish this by coming into contact with a living cell and getting their genetic material into the cell so that the cell makes copies. The virus takes advantage of gates that the cell uses, so that each time the cell makes a copy of itself, it also makes a new virus. The virus accomplishes infection by finding a receptor molecule on the cell’s surface. The virus must have the ability to find and use a receptor, otherwise no infection can occur. In order to prevent an infection, there needs to be a means to prevent the virus from binding with the receptor. This is far more difficult than it may sound, as viruses like Ebola can bind to a number of receptors on human cells. This makes viruses like Ebola, Marburg, and HIV both versatile and highly aggressive. This also makes studying Ebola in a lab very dangerous.
This most recent outbreak is the first time that any form of Ebola has spread to an urban area. Like any other human-infecting virus, a large, closely packed population allows the virus to spread faster. Tracing the path of infection, identifying the infected persons before the infections spreads, is far more difficult. In a fluid, global population, infected persons can travel across the globe before the first symptoms appear. Add the issue of a lack of effective treatment; most African nations suffering from outbreaks lack adequate facilities; isolation wards, adequate medical personnel, and a lack of labs make viruses extremely hard to identify and contain. Add traditional rural practices that are a part of the death rituals, like washing a dead relative’s body by hand before the burial, also increase the transmission of infectious disease.
What can you do?
Educate yourself. Know the symptoms of Ebola, and other infectious diseases. Prevention focuses on avoiding contact with the viruses. To prevent infection and spread of Ebola and other viruses, you must avoid exposure. Avoid areas of known outbreaks. As with other infectious diseases, frequent hand washing with soap and water, or the use of alcohol-based hand rubs containing at least 60% alcohol when soap and water aren’t available. If you live in an area of initial infection, avoid bush meat or contact with possible vector animals, including nonhuman primates that are sold in local markets. Avoid contact with anyone infected, caregivers should avoid contact with the infected person’s body fluids including blood, semen, vaginal secretions and saliva. Ebola infected persons are most contagious in the later stages, when the disease creates the greatest discharge of bodily fluids like stool, mucus, and in some cases, blood.
If you are a health care worker, protective clothing including gloves, masks, gowns and eye shields are critical. Infected people must be quarantined from others, and all materials must be sterilized. Do not handle remains; bodies of patents having died from Ebola are still contagious. Only specially organized and trained personnel should bury the remains, using appropriate safety equipment. Think like an epidemiologist!