And...cue the uninformed, ignorant masses to protest, criticize and incite fear. People with platforms to express themselves are even irresponsibly leveraging this fear to further provoke criticism of the handling of immigration. Here's but one example, courtesy of Laura Ingraham, from The Laura Ingraham Show, 8/4/2014 (horrific grammar is hers):
"All the people who are upset about the Ebola-infected patients being treated in the United States. I will say this, at least we know who they are and where they're being treated. We currently have a border that is much like Swiss cheese that anyone could be coming across the border right now, with any type of illness. And we have a very limited ability to stop them, track them, prevent the disease from spreading. So before you get all upset about Ebola, we could have Ebola people coming across the border right now."
What terrifies me is the blatant disregard for the truth and the perpetuation of ignorance, by people who should know better.
Actual experts in the pertinent fields: epidemiology, virology and emerging infectious diseases, are trying to get the truth out, but the voice of reason is hard to hear over the din of doomsday propaganda extremists. Clearly, we need to learn a little more about Ebola and the real, or imagined, threat to those of us here in the U.S.
My friends, I'm here to help. But before I get into the nitty gritty, let me first say this:
The current Ebola epidemic in West Africa will not lead to an Ebola epidemic in the U.S..
And how can I be so sure?
I have a PhD!
Just kidding. Well, I do, but that's not why I can say that. In order to understand why we are not currently at risk for an Ebola epidemic here in the States, we need to understand a little bit about the virus. Virus life cycles and the processes of transmission and infection are very complex and one blog post cannot address every aspect. Therefore, what follows is a brief description specifically designed to help us understand what's relevant for this discussion.
What is a virus?
A virus is a microscopic infectious agent that can only make copies of itself (replicate) inside of a living cell. Who cares? Well, the only thing a virus has on its agenda is to replicate. That's it. Once it replicates it can get out and see the world! To do this, a virus hijacks cellular machinery for its own dastardly purposes, makes millions of copies of itself and enters a new organism through transmission and infection. Every type of organism on earth can be infected by a virus, including bacteria. Cool, right? Because a virus cannot replicate on its own, most experts do not consider it to be "alive" although I'm sure the debate still rages somewhere. Oh, and by the way....ascribing human characteristics to a virus (e.g, its agenda and dastardly purposes), while fun, is a no-no. Viruses are passive. Their genetic code dictates what the virus particle does in response to environment stimuli, but they don't make plans or actively do things, although some of them make us very sick or kill us. Kinda like Congress.Many viruses that infect mammals, (e.g, humans, gorillas), survive in nature by residing within a "reservoir" organism: an animal that is not sickened by the virus, but can carry and transmit it. The virus replicates in this reservoir and when there are enough virus particles in the right places, they are "shed", or released via saliva, urine, feces, sweat, tears, semen, mucus etc. The specific route of shedding depends on the virus and its tropism (where it goes in the body). So even though the animal harbors the virus, it doesn't get sick (also called "asymptomatic") and it can infect other organisms.
[EDIT 8/12/14- I moved the detailed info about aerosol, droplets and fomites to a dedicated post and expanded upon it both to make this post easier to read, and make that information easier to find. End Edit]
What Does "Airborne" Mean?
Let me clarify. Bodily secretions that make it into the air from various orifices (e.g., nose, mouth, John Boehner) are called droplets and are classified based on size and distance traveled. The smaller the droplet, the longer it stays suspended in the air, the farther it travels and the deeper into the respiratory tract it can go upon inhalation by the person sitting down the aisle from you on the airplane.
When we say that a virus is airborne, we specifically mean it is capable of aerosol transmission via inhalation, even when not in close proximity to the source of the aerosol.
Large-droplet transmission happens when heavier droplets are splattered or splashed onto people or surfaces and is not considered airborne.
So, is Ebola Zaire airborne? No. While it is possible that the non-virulent (doesn't make you sick) Ebola Reston strain was transmitted between primates that were not in close contact in a small monkey outbreak in 1989, other modes of transmission couldn't be ruled out. In addition, it did not cause clinical symptoms in humans that were exposed. If you want to read more about that, check out Richard Preston's The Hot Zone. I agree that Richard has a flair for the dramatic, but he gets much of the detail right. In 1996 one of the world's pioneers in the field (and my PhD Adviser), CJ Peters and his group, published a paper characterizing Ebola infection in cynomolgus macaques (a type of monkey). They had this to say, "...abundant virus was visualized in alveolar interstitial cells [cells found in the lungs] and free in the alveoli suggesting the potential for generating infectious aerosols. Thus, taking precautions against aerosol exposures to filovirus infected primates, including humans, seems prudent." There have been other studies, and anecdotal evidence during epidemics, also showing evidence that aerosol transmission of Ebola might be possible.
So then it IS airborne, right?
Nope. We've yet to see aerosol transmission actually happen during an outbreak. Experience shows us that it doesn't happen. [edit 9/18/14: For more clarification on this my post on the 1995 Kikwit outbreak]. So while the wise thing to do is caution people to take precautions against infectious aerosols, direct contact, large-droplets and poor sanitation are the culprits here.
1.) There are significant differences between the diseases caused by Ebola Zaire in pigs compared to that in monkeys and humans. In primates, Ebola Zaire causes widespread severe immune dysregulation that leads to hemorrhagic fever and in 90% of cases, death. In pigs, however, the disease is very different: infection is limited to mostly the respiratory tract and illness lasts for about 9 days and then the animals recover. This clearly indicates that there are significant differences in the way the virus spreads through the body and causes disease in the pig compared to the primate. Unfortunately one serious design flaw in this study, that was pointed out by the authors, was that "The design and size of the animal cubicle did not allow to distinguish whether the transmission was by aerosol, small or large droplets in the air, or droplets created during floor cleaning which landed inside NHP cages (fomites)." In addition, the principal investigator (head scientist on the study), Dr. Gary Kobinger, indicated in an interview in 2012 that, based on the kinds of respiratory secretions that pigs produce, he believes the transmission they observed between pigs and monkeys was via larger droplets.
and 2.) The observation also made by the study authors that, "Interestingly, transmission between macaques in similar housing conditions was never observed." Yeah, that IS interesting!
And it was CONFIRMED in a recently published study!!!! Primates do not transmit Ebola to other Primates via aerosol transmission. The End. [EDIT 8/8/14: I realized after posting this that I was missing a golden opportunity to communicate a very important scientific concept regarding these studies. It's easy for non-scientists to look at this example and think that the 2012 pig-monkey study was either wrong or useless, but the truth is, it was a great study. The problem was that people with no scientific background, heard about it and assumed it gave us information about human-to-human transmission. Therein lies the problem. The study gave us very important information about their model under their conditions, and the authors were clear about its limitations, as good scientists are. The takeaway is this: be careful about extrapolating data from model systems to humans, and be more careful about spewing those extrapolations out into the world. End Edit]
So these are the protective measures you need to take....if you are in West Africa:
So what does this mean for a potential U.S. epidemic? It comes back to this: Close contact with someone during the infectious stage of disease is necessary for human-to-human transmission of Ebola. This is one of the key reasons why the Ebola epidemic in West Africa is out of control and why this won't happen in the U.S.
Unfortunately, in West Africa, one major problem with this epidemic was the lack of effective diagnostics and isolation at the beginning of the outbreak. These countries simply do not have the resources. Many infected people moved around before anyone knew the disease was present and more people got infected. By the time clinics and treatment centers were set up, the numbers of patients shedding virus into the environment were too high, and sanitation too inadequate, for the limited precautionary measures being taken. Not all health care workers have access to protective gear at all times and the gear they get is often meager. Disinfecting protective gear by hand is the only option, but it just isn't effective on that scale. There are also enduring cultural practices that contribute to disease spread, and when combined with inadequate infectious disease containment infrastructure the results are tragic. Richard Preston's recent New Yorker article does a great job of helping us understand this reality. If that weren't enough, all of the everyday struggles these people face compound the problem: weather, restricted access to clean water, sanitation, ongoing civil/political unrest and the list goes on. For a nice in-depth explanation read Laurie Garrett's article from last week. You probably remember Laurie from The Coming Plague, also
Can you begin to see how this won't happen here in the U.S.? We screen people at our borders and ports of transit. Suspected cases are immediately isolated in facilities that actually have the resources necessary to do so effectively. People have the luxury of information here and are quick to get themselves or their family members to the hospital because they understand what's at stake. Physicians are well trained and even more well equipped. Protective gear is either disposable and disposed of correctly, or used once then sterilized, not merely disinfected and certainly not by hand. Patients are isolated under stringent conditions and are provided superb supportive care that includes sanitation and cleaning measures. Simply put, the U.S. has the resources needed to handle Ebola patients in a way that will prevent an epidemic. The worst that could happen is a small outbreak in which a few people are infected before they are correctly diagnosed and treated. But once discovered, we would be able to effectively stop Ebola from spreading. So relax people. Seriously.
One last thing I'd like to address is the fear of a naturally occurring worldwide epidemic (pandemic) of Ebola. Also, not going to happen, and the physicians out there claiming it is coming should be ashamed. An important factor that reduces the potential for an Ebola pandemic is that Ebola isn't actually very good at being a virus. When it infects and sickens an organism, it kills it quickly. It renders the patient sick enough, fast enough, that transmission is actually limited. Sure it will spread through heavily populated areas quickly under the right conditions (lack of resources, sanitation, leadership, medical care and effective preventive measures), but it will burn itself out eventually and it certainly won't spread that easily in developed countries. If you are interested in this concept I highly recommend checking out the game Plague Inc in which you can design an infectious agent and give it different properties that will affect severity of disease, transmission route and rate and ultimately demonstrate why the agent either does or does not cause epidemics. It is a bit morbid, and I'm not sure how I feel about my husband and son shouting for joy when they "win" because their infectious agent decimated the world. Nonetheless, it's based on real world epidemiology models and is a very practical way to learn about the fundamentals of infectious disease epidemiology. If you plugged Ebola's characteristics into the system, it would demonstrate that Ebola is self-limiting.
So, instead of fear mongering and hate-filled political rhetoric, let's focus on being compassionate to those who are suffering. Just because we aren't expecting an epidemic on our soil doesn't mean we shouldn't be working hard on behalf of those facing the disease right now. Let's celebrate the heroes who are already there, working tirelessly under horrific conditions with severely limited resources and focus our energy on helping. They can't do it alone. Let's quiet the divisive ignorance, and act. Each of us can make a difference in the lives of those in need. The question is, will we?
Go to these websites to learn how you can help:
Africare
Global Giving
Direct Relief
Action Aid
Update 8/20/14: Here's where to go for great specific info about how you can make a difference:
Caitlin Rivers Thanks Caitlin!!
And for more great updates on this and other infectious disease topics I highly recommend Tara Smiths' Aetiology Blog. It's well written and insightful!
I'm curious why Ebola seems so much much easier to transmit than aids. From what I've read, both spread via contact with bodily fluids. Is it related to how many viruses are needed to cause an infection?
ReplyDeleteHi and thanks for the question.
DeleteYou are correct that they both spread through bodily fluids, but there are differences. Infectious HIV particles can be found in blood, pre-seminal fluids, semen, rectal fluids, vaginal fluids, and breast milk. Ebola is found in those as well as others including sweat, tears, respiratory tract secretions and saliva. You might be able to see then, how HIV transmission, mostly through sexual activities, is more limited than Ebola. Ebola on the other hand can be spread through sex but also through all other fluids, which patients lose a lot of through sweating, vomiting and diarrhea, which generate a lot of droplets/aerosols/fomites. In addition, Ebola patients require serious care while they are ill, bringing more people into closer contact. So the types of infectious fluids and the symptoms themselves, combine to make Ebola far more easily transmitted than HIV. Your question about infectious dose is a good one. We know for Ebola that dose is 1-10 individual virus particles, but for HIV it's still unknown. I imagine Ebola has a much lower infectious dose, but even if they are the same, the other reasons I outlined would be enough to cause the disparity in transmission. I hope this helps.
Very interesting that ebola gets into so many more nooks and crannies! Thanks for answering. I really enjoy your site.
DeleteYou are very welcome and thanks for stopping by and asking great questions. It's what makes this enjoyable.
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