字幕表 動画を再生する 英語字幕をプリント What I'm going to talk about here are the characteristics and traits of pandemic pathogens. You just heard my colleague Crystal's talk where she introduced the concept of GCBR. I'm going to try and delve very deep into that concept, to try to understand what is it about certain pathogens that allows them to cause a GCBR? And I think the theme of this conference is to be curious, and that's really what motivated this project, was to be very curious about what goes on there. I have a picture of my blog there, Tracking Zebra, if you're interested in infectious disease, I do write a lot about that, and that's my Twitter handle. The aim of this project was really to develop a whole new framework around the traits of naturally occurring pandemic pathogens that could constitute a GCBR in order to change preparedness activities. In the past, I'm going to talk about this a little bit later, we've really focused on list based approaches, that are largely derived from the former Soviet Union's biological weapons program. There hadn't been a lot of fresh thinking. It was very static. I think that's what we tried to do in this project. So a couple of basic definitions, just because I don't know if everybody has a biological background. Pandemics are infectious disease outbreaks that occur over a wide area and affect a large proportion of the population. It doesn't necessarily have to be severe; 2009 H1N1 was a mild pandemic, but it was still a pandemic. An epidemic is an infectious disease outbreak that occurs over a large number of individuals within a population. So, the SARS outbreak in 2003 would be an epidemic. An endemic is something that occurs regularly within a population. For example, the common cold is endemic in the human population. Those are just things to keep in mind. What we're talking about are specific types of pandemics that are very severe for the GCBR, to meet GCBR criteria. I'm not going to spend much time on this definition because Crystal really went into some great detail, but what I'm going to do is really expand on what is it about those biological agents? What types of biological agents can cause GCBRs? Everybody is very focused on viruses, some people are focused on bacteria, some people on other things, that's what I'm trying to understand is what traits does a biological agent have to have in order to be able to cause something this severe, to cause this massive catastrophic loss of life, disruption of society, that type of analysis. I just want to draw a distinction, because what I'm talking about here are pathogens of pandemic potential, versus what's this distinction that was made in Mike Osterholm's recent book about pathogens of critical regional importance. When you have an outbreak like Middle East Respiratory Syndrome, that doesn't mean... just because it's not a GCBR doesn't mean it's not important or that it's not going to be very disruptive to people's lives and to societies and to governments. But what we're talking about in the GCBR is something that's going to be global, like the 1918 flu. Something that's a lot different in scale than even Middle East Respiratory Syndrome or SARS. Something much different. There's lots of pathogens of critical regional importance. Even the Ebola outbreak in 2014 in West Africa falls under this type of criteria, versus this type of criteria. The specific aim with this project was really to, like I said, move away from this list-based historical approach. People had really just taken the Soviet Union Biological Weapons program and added a couple things here and there, but really hadn't thought much about why were these things on there? Challenge the assumptions that put them on there, and really try to understand what was it that made smallpox so scary? What was it that makes pandemic flu so scary? We really try to go into an inductive manner, trying to make a whole new paradigm, looking at the actual attributes. We tried to do this by being totally microbignostic. What I say microbignostic, that means we didn't go into this project saying, "This has to be a virus. This has to be a bacteria". We said it could be anything. It could be a parasite, a protozoa, it could be a prion. So that was something that was totally new. We really wanted to challenge thinking and then take this paradigm, and hopefully use it to move forward when we think about preparedness and try and think of new infectious disease outbreaks with this new paradigm in mind, to get better at being prepared because we're constantly surprised, which I'll get to later in the talk. What are the essential traits? The next slide is a little busy. I'm going to walk through it one by one. Thinking about what does it have to have? Talking to people and doing a lot of literature review, there's a whole bunch of different things that make up the alchemy of a pandemic pathogen. I'm going try and explain what this equation means and all of this as best I can. The first thing you need to do, is you have to have a pathogen that can efficiently transmit from human to human. You can have a disease that can be really bad like Tetanus. That doesn't transmit between humans, so it can't be a pandemic pathogen. When you're talking about a pandemic pathogen, it has to be able to get from people to people, so that's number one. It has to have a moderate fatality rate. It doesn't have to be really, really horrible like a 90% fatality rate or 100% like rabies. It has to be something that's kind of in a sweet spot that it allows enough death to occur that it causes disruption in the society. Remember that the 1918 Influenza pandemic, which killed 50 to 100 million people, only had a fatality rate of two percent. But because it was so widespread, it led to disruption. Contagious during incubation period. I have bolded this because in multiple modeling studies, and in experience, and Crystal alluded to this earlier when she talked about smallpox, if a disease is contagious during the incubation period, when you're not sick, it's very, very hard to control. That's why the H1N1 pandemic had spread everywhere before anybody even knew about it because people were contagious one day before symptoms. If a disease is contagious in that period, it becomes very, very difficult for public health interventions to have any impact. The same goes with mild illnesses with contagiousness. When you have the flu or the common cold and you're out shopping, doing your normal daily life, you spread that to other people. It's very hard to stop that, versus something like Ebola, when you're sick and highly contagious you are in bed and you can't really move, and move about in society. So this is another key factor. An immunologically naïve population. Again, reflecting back on Crystal's talk when she showed the map of the indigenous populations in the Americas, in the pre-Columbian area in 1492. That was an immunologically naïve population to smallpox, which allowed smallpox to spread very rapidly through that population. That's what a pandemic pathogen would require. No vaccine or treatment. You don't have any way to stop this. That's another thing that fits into this. Correct atmospheric and environmental context. Infectious diseases happen in a context. Is it happening during World War I like the pandemic flu did in 1918? Is it happening where there's been societal disruption? Like, for example, Yemen right now and the Cholera outbreaks? All of that's going to play a major role in how prolific an infectious disease outbreak is. There's a lot of biology that has to go into this too. Not every pathogen can infect every type of human. You have to have a proper receptor. So you've got to have some receptor that lots of humans have that this virus or this bacteria can actually cling onto. It's also going to explain which organs it affects, because obviously some organs are more important. If it affects your brain, your kidney, your liver, your lungs, those are what you really see with these pandemic pathogens. And then it has to be able to evade the host immune response. It has to be something that is not easy for the immune system to mount an effective response against. This is a fancy equation that showed up. The point of this equation is not to memorize it or to think about it, it's just that you can take all of these things and give them values, and come up with pandemic potential of a pathogen. You can look and vary them. If you look at some other things, for example, the more host types a pathogen has, the more chance it is to emerge. That's another thing that comes up, that these things can infect more than one type of species. That's where the concept of zoonosis comes about, where something comes from an animal species into humans. But the more hosts something has, the more likely it is to be able to infect humans and cause a problem. Thinking deeper about this. We have that recipe there. When you think deeper, there's a couple of things that come out of this. When you look at the way these things transmit, the most likely way to cause a pandemic is for it to be done through the respiratory or the airborne route. There's much, much less you can do to stop an airborne virus or a respiratory droplet spread virus. If I had measles right now, you would all be exposed. It's very, very hard to do that. But if it was something that was spread through, for example, fecal/oral, like Hepatitis A or Cholera, you can really delimit that with sanitation. Remember, there was a couple of cases of Cholera in Mexico about five years ago, and everybody panicked. But there was just even a modicum of sanitation - stopped Cholera. It did not spread in Mexico. You can't do that with respiratory viruses and airborne viruses. It's much, much harder through the respiratory or airborne bacteria. A vector borne transmission, so that means through mosquitoes, through ticks, that's something that's very interesting and it is something that I think we struggle with trying to figure out exactly how bad a vector borne outbreak can get. They are, in general, limited by the vector range. For example, mosquitoes frolic in places that are going to be much more conducive to their habitat, so it's going to be very hard for them to live in a temperate climate. I live in Pennsylvania, we don't have mosquitoes year round there. But there are parts of the world that mosquitoes thrive in all year round. That's why I talked about specifically aedes mosquitoes, which are the mosquito that's responsible for spreading Dengue, Chikungunya, Zika, Yellow Fever. They are basically covering half the population of the globe. That is something that's a little bit different with vector borne. In general, we don't think vector borne could do this because the host range, the range of the vector, is kind of limited. The other thing to think about is, talking about global catastrophic biological risk, we talk about deaths, but is fatality everything? This is a question to pose to yourself. There's two purposes for an organism. To survive and to reproduce. What if you had a disease like Zika? It was much more widespread. Or Rubella? Pre-vaccine. If you decrease the reproductive fitness of a species, could that lead to a GCBR? I think the answer is yes. I don't think that Zika or Rubella really make that criteria, and maybe if we were talking about this, if Rubella occurred now, maybe it would fit in the GCBR. But back in the 1960s, people coped with Rubella, but it is one way to think about a GCBR that doesn't end up killing everybody. The other thing is, there's another virus, HTLV, which as been in the headlines a lot in the last couple of weeks because of some studies that have come out of Australia. HTLV is the most carcinogenic virus. It causes human t-cell leukemia. This was the first human retrovirus that was discovered. What if an infectious agent causes cancer in everybody? Would that lead to a GCBR? That's something just to think about, that it's not always going to necessarily be death. I think you have to be very broad and active minded about this. There's also something I wanted to talk about called sapronotic disease. That's a term that we found from the plant world and the animal world, where you have this idea that if an infectious agent is killing everybody that it's infected, it's not very good because it's going to run out of people to infect. But what if it doesn't care? What if that's a secondary source? What if it's an amoeba that eats things in pond scum, but only intermittently infects humans? Like the brain-eating amoebas that always grab headlines? How does that fit into this? If it doesn't necessarily need to be in humans to thrive. That it has other things. It could eat dead bark on a tree, or it can eat stuff on the bottom of the forest floor. That's another way to think about a pandemic pathogen, I think is really interesting that came out of this talk. The first set of conclusions we drew from this project were, the traits that are most likely to be possessed are going to be respiratory droplet transmission, fecal/oral much less likely. The aedes vector-borne agents, those mosquitoes, have a special status because there's widespread mosquito prevalence and there are certain viruses that get very high levels in your blood that these mosquitoes can just kind of pick off. That's why we've seen explosive outbreaks of Dengue, Chikungunya, Zika, why we've seen Yellow Fever resurface. So they are a special category. They probably don't fall as high as respiratory/droplet, but that's something to keep in mind, that these could possibly do that. So then the next thing we try to do is think about, okay, we've said respiratory/droplet transmission. So we have to make a choice, we have to think: is it gonna be virus, bacteria, fungi, parasite? So I say there's no agnostics in a foxhole. We had to push people that we talked to in this thing, and push ourselves to think, what would it really be? So I think that viruses are very formidable in this realm. They mutate much, much more rapidly than bacteria. The transmission and replication cycle in a human is much faster than in bacteria. And you heard this earlier today, that there's no real broad spectrum antiviral agent. I have a picture there, this is from Epcot Center, for penicillin.