Ebola, Emergent Viruses, and the Threat of Global Pandemic
For the past 50 years, emergent viruses like Ebola, Hanta virus, and AIDS have caused epidemiologists and other scientists increasing concern. Although we do not know what the agent will be when it happens, the threat of global pandemic is real. Many experts believe the question is not 'if' but 'when', and 'what will we do about it when it strikes'.
Emergent viruses are diseases that show up in humans seemingly for the first time. Most often they are the result of a virus opportunistically 'jumping species', from an animal host into a human body. The host may show no symptoms of illness at all, yet carry the virus in its body and its bodily secretions.
For example, ticks carry Lyme disease, even though the ticks themselves are not sick. When a host tick bites a human being, Lyme disease can be transferred to the human, who then becomes illl.
Some viruses require what is called an 'amplifier' in order to become dangerous to humans. An amplifier is an intermediate animal that catches the virus and becomes ill. The amplifier animal then produces the virus isn such huge numbers inside its sick body (in other words 'amplifies' the virus) that the virus becomes a danger to humans.
Ebola is thought to be such a virus. While the host is not known for certain, fruit bats are a prime suspect. Assuming fruit bats are the host for ebola (which they might not be), a fruit bat may bite a monkey or ape. The monkey then becomes ill with ebola.
The monkey amplifies the virus many thousands or even millions of times inside its own body. If a human then eats the monkey, which some people in Africa do (monkeys and other wild animals are called 'bush meat' and are routinely sold for consumption in African markets), or is bitten by a monkey, the human will come down with ebola.
Viruses are incredibly small and can only be seen under an electron microscope. The period on the end of this sentence, for example, can hold over a million ebola viruses. Since it only takes one to infect a person, that makes a virus like ebola, which kills between 60% and 90% of the people who get it, very, very dangerous.
When a virus jumps from an animal to a human being it is called 'zoonosis', a term most people have never heard but which is sure to become more common in future decades.
Facts About Ebola
Ebola is a scary virus, no doubt about it. However, most strains of ebola are not easily transmitted by air. In order to catch ebola, you have to eat an infected animal, be bitten by one, or come into direct contact with the vomit, blood, or other bodily fluids of a person with active ebola symptoms.
However, a few exceptions do apply.
Researchers in Canada recently found that airborne infection of ebola could be induced in pigs exposed to fluids in coughing. This is not standard and so far has happened for certain only in a laboratory.
One strain of ebola, the Reston virus, does spread by airborne transmission. However, at this date, it has only been observed in monkeys and seems not to affect human beings, even when they have the virus in their bodies as a result of direct contact with sick animals.
Ebola mutates easily. The scariest scenario would be the emergence of a mutated ebola strain that killed humans via airborne transmission. So far, that strain has not shown up.
So why are people so frightened by ebola?
- Even though ebola is harder to catch than, say, the flu, ebola has a very high fatality rate. Depending on the strain, ebola can kill up to 90% of the people who contract it.
- Ebola symptoms show up between 3 and 21 days after exposure to the virus, so a person with ebola would theoretically have plenty of time to travel to a new country before developing symptoms. People with ebola are not contagious until they develop symptoms.
- Early symptoms of ebola infection mimic the flu: Congestion, coughing, headache, fever. This makes ebola easy to ignore for a time, even after it becomes infectious.
- Ebola symptoms quickly progress to vomiting, bloody diarrhea, rash, psychosis, and skin lesions. Late in the progress of the disease the eyes become bright red and the internal organs begin to liquefy as cells are destroyed by viral replication.
- A person in the late stages of ebola bleeds out from every orifice and vomits copious amounts of blood. At this late stage many brain functions are gone or damaged because the brain itself is liquefying. The virus literally digests the person while he or she is still alive, then jumps into another person through contact with blood or fluids and starts the process all over again.
- Many people in Africa become infected by handling the dead bodies of ebola victims in traditional ways. Touching a dead body and getting fluid into a cut or into the mouth or nose can transmit ebola.
- Ebola stays active in male sperm for up to two weeks after recovery. So even men who are lucky enough to recover can transmit the virus to their sexual partners for two weeks.
- No cure or vaccine for ebola exists. Treatment involves supporting the patient by administering fluids and alleviating pain. Some experimental success has been shown via treatment with blood serum from survivors. The hope is to transfer antibodies in the serum to the sick person to fight the disease. However, since there are few survivors, and since this treatment is still experimental, it is not a panacea.
- No vaccine is available for ebola. Vaccination will be problematic because, like the flu viruses, ebola mutates easily into new strains.
- Human ebola has never taken hold in the U.S. However the Reston strain showed up in a facility housing monkeys just outside Washington D.C. in 1989. Had the Reston strain turned out be Ebola Zaire as first thought (Ebola Zaire is the most dangerous strain), the U.S. would have had its first Ebola outbreak back over 20 years ago.
For more information about ebola and specifically how the Reston strain came to the U.S., read The Hot Zone by Richard Preston.
Test Your Knowledge
Ebola can be cured with:
The Greater Threat of Global Pandemic
Because ebola does not spread through the air like the flu, it will probably not be the next global pandemic. However, that does not mean everything is fine.
Scientists are discovering that emergent viruses often occur in areas where deforestation occurs. Why would this be the case?
Viruses can go dormant for a long time, just waiting for a viable host to come along. The ebola virus, for instance is millions of years old, and although we can't know for certain, it seems that for most of those years it did not bother people.
However, changes in the environment can cause viruses to mutate and jump into new hosts. Many emergent viruses have come from parts of Africa where the environment has been deforested for farming and native animals have been killed off in large numbers. Ebola is one of these viruses. AIDS is another. Other dangerous viruses have emerged from the deforestation of the Amazon.
Another way that viruses emerge from their hiding places and jump to humans is through the introduction of invasive or non-indigenous species. These new species can serve as amplifiers for viruses that formerly left people alone.
The monkeys in Reston, VA that had ebola in 1989 were viral amplifiers. Monkeys are not indigenous to the U.S., but we import and use them for medical research. If the monkeys we import are sick with a virus that jumps to people, that virus can infect Americans.
Finally, because the world is getting smaller and smaller through air travel and world trade, any virus that emerges anywhere is a short plane right away from anywhere else.
Includes Reston VA Ebola Outbreak
How Viruses Jump from Animals to People
What Can We Do About Viral Threats?
The first thing we can do is inform ourselves through reading, talking with doctors and experts, and thinking about the problem calmly.
We can also stay calm.
Panic is a problem in itself, and epidemiologists know that when a dangerous virus emerges some of the worst problems are caused not by the virus itself, but by the panic and fear that virus can induce in a society.
For example, in Africa, some people with ebola are panicking and fleeing because they think medical workers are the cause of the disease. This only insures that ebola will continue to spread across West Africa instead of being contained where it can burn out and stop, at least for awhile.
Another important step we can take is to lobby for health reform and readiness. RIght now, most countries are not at all ready for a global pandemic, even though scientists have been warning that such an event will almost certainly occur. Organizations like the CDC and WHO are not adequate to address every emergent virus around the world. We need a saner, more comprehensive approach.
In the U.S., we don't even have adequate medical care for people who have ordinary health problems. Emergency rooms are packed on an average day and we are still trying to solve these basic problems instead of ramping up for an epidemic.
A good first step would be to figure out how to get comprehensive care to our people in the absence of a pandemic, so that if a pandemic did strike, we would have better chance of dealing with it. We could also take seriously conditions in poor countries, not just because it is the humane thing to do, but because we are all at risk.
Another good step would be to agree to halt deforestation and the killing of native animals. This seems unlikely, yet if we allow these things to continue, new sicknesses will continue to emerge and devastate human populations.
The world is changing rapidly and it is easy to get overwhelmed.
Focusing on what we can do, instead of what we fear, is one option for moving forward.
We no longer live in an age in which problems in Africa or the Amazon or the Arctic are none of our concern. We all live on the same small planet. We need to respect and care for it, and for each other. The world will be fine. With or without us, viruses will survive another million years without any problem.
The verdict is still out.
- All the Virology on the WWW : Emerging and Infectious Disease
A collection of WWW sites with information about emerging and infectious disease from All the Virology on the WWW.
- Ebola Hemorrhagic Fever | CDC Special Pathogens Branch
- Ebola hemorrhagic fever: MedlinePlus Medical Encyclopedia
- Ebola Hemorrhagic Fever | CDC
Information on Ebola Hemorrhagic Fever (Ebola HF). Provided by the U.S. Centers for Disease Control and Prevention (CDC).
- WHO | Ebola virus disease
WHO fact sheet on Ebola haemorrhagic fever: includes key facts, definition, transmission, symptoms, diagnosis, treatment, prevention, WHO response.