DREW HARVELL: Thanks to all of you for coming. We really appreciate your help in getting the word out and helping us communicate the kinds of research that we do. I'm wearing my hat as the Associate Director for Environment in the Atkinson Center, I just want to take a second, sort of a commercial break here, just tell you a little bit about the Atkinson Center.
This is now a four-year-old center at Cornell, and the goal is to advance multi-disciplinary research. Ideally we like to really advance broad disciplinary research, so engineers working with economists, working with environmental scientists. This project is an example of one of those. We're not engineers, but we do represent a range of different disciplines, and there's a modeling component involved in this project.
I'll be happy to tell you more about the Atkinson Center later if anybody has questions. For now I want to just head on into this talk. Please interrupt us at any time. The real goal is to interact with you and communicate as best we can our message and the information we have. And if it helps to ask questions, please do. This should be very informal.
So our talk today is entitled A Warmer World Is A Sicker World. [INAUDIBLE] and I are the two speakers. And maybe you could think of it, Or When Is a Human Like a Coral? A lot of you, I know, have come-- you're interested to hear about the potential chikungunya virus outbreak, I'll talk about that. But I'd also like to frame this as a broader question in climate change and disease, including wildlife as well as humans. We're not going to spend a lot of time talking about the climate itself. I think we've reached the point-- the economist even agrees that no matter how you measure it, the earth is getting warmer. And that's sort of the main climate driver we're going to be talking about today.
So why is a warmer world a sicker world? One thing I'd like to point out about sort of basic disease interactions is there's always this triad involved. There's a host, whether it's a human or coral. There's a causative agent, whether it's a virus, a fungus, a bacterium, some kind of an infectious agent. And the reason we're here today is because this interaction is very sensitive to the environment. And so when there are changes in the environment, whether it's warming oceans, acidification, changes in nutrients-- and the observation here is that many diseases are sensitive to warming.
The premise of the project that Laura and I and a colleague of ours, who isn't here that works on frogs, started with in this project is that there are particular source of disease interactions with climate that can be sentinel systems. They tell us-- they're the canary in the coal mine that tell us about change on our planet, change for good or for bad. They can affect humans as well as the environment. And particularly informative disease sentinel systems are the coral disease outbreaks, because they're very sensitive to climate warming. One or two degrees temperature will tip them over into an outbreak stage.
Human vector borne diseases are also very sensitive to warming, as Laura will talk about. And then we're not going to talk about the frog chytrid outbreak, but this is an example of a series of disease epidemics worldwide that is essentially driving a group of organisms, the frogs, to extinction. And this is a project that's led by our third colleague, Kelly Zamudio, who's not here today.
So this is our roadmap for our plan. So we're going to talk about health as the sentinel of climate change impacts. I'm going to start off by talking about what could be called a rising tide of ocean diseases. First-- and I'm going to go through this pretty quickly, because I know you don't want to just sit here and listen to us talk-- I'll talk about the ecosystem threats to coral reefs that are particularly relevant because of the disease issue.
And if coral reefs are not the one that's most interesting to you I'll also mention briefly some serious challenges with oyster fisheries. And actually, the most emailed article today on the New York Times was about a dolphin and bird mass mortality of Peru, so this is also very timely. And then Laura will talk about the human health issues associated with climate change, and particularly the example of chikungunya being bad for your health.
And I just want to make the point, I'm an ocean biologist, so I work in the oceans. And I often find-- here I am at Cornell University, I often find the oceans are a little bit out of sight and out of mind. And so I just want to remind you, since last week we were working on this climate change assessment for the oceans and I was kind of looking at the exclusive economic zones of the US, and thinking, wow, the US really is an ocean country. We are bounded on virtually all sides by very rich oceans, as well as having very large holdings in the Pacific with some of the Pacific Islands. So I just wanted to make that point.
So I opened up The New York Times this morning to find this, and I thought well that sort of fits within the realm of what I was talking about today. Essentially this article describes a large die off of dolphins and birds. These were in Peru. And this is sort of a case in point of where these very rapid outbreaks can occur. We can have large scale mortalities. And these are the kinds of things that we're predicting will increase in warming oceans. Now we don't know, we haven't gotten to the bottom of this mystery yet. I'm just giving you this as an example of some of the newsworthy issues associated with this.
This is an article I had in 2010, that was right on the eve of a big warming event that probably a lot of people didn't know about, because it was largely being played out in the Caribbean. We had the warmest year on record and massive levels of bleaching, which, when we followed these corals in Curacao and throughout the Caribbean six months later, we had a 30% loss of life cover, of coral cover, and outbreaks of disease. So this is kind of an example of the sorts of climate related situations that are driving our coral reef ecosystems to an unstable level.
And I wanted to give you an idea of how we see temperature from space. One of the interesting things about the ocean is that we can measure the ocean skin surface temperature. And so I regularly get these plots from NOAA, and what they show-- this was kind of the peak of the 2010 event, which was the most extreme series of temperature anomalies we'd had. And this pink area is 16 degree heating weeks. That means 16 successive weeks where we had warmer than average temperatures.
Now corals will show stress and bleaching at four to eight degree heating weeks. So this was a massive event. And then when we followed it, in the-- it's not actually working. That big pink area is where Curacao is, there were large outbreaks of coral bleaching and [INAUDIBLE] disease. And just to show you this plot along the bottom, it gives you an idea of the kind of heat stress we've had for the last 25 years. And I'd like you to be impressed by the fact that these are getting bigger and bigger and bigger, and that we're having our biggest events in the last few years.
And this is what it looks like underneath the surface of the ocean when we dive down and monitor the reefs. So essentially all those corals are white. Does everybody know what that means, that they're white? Any questions about that?
AUDIENCE: They're dead.
DREW HARVELL: No, they're actually still alive. So these corals are alive, but they've expelled the symbiotic algae in their tissues that give them the color. So they're still alive as long as they don't get hit by a disease which then kills them. But of course the next thing I'm going to tell you is then what happens is that their immunity is compromised, and they get hit by a disease that then kills them. But under normal-- if the warming succeeds in the winter, as it does-- secedes, then these corals can recover algal symbionts and they can survive.
But this is what happens when they pick up a disease. So these are lesions caused by a bacterial infection. And my colleague Ernesto Weil actually measured the rates of those lesions, the rates at which the coral loses its tissue. And the interesting thing about this, if you look at this plot that started-- he started measuring this in 1999. This is the lesion growth rates through time. What you see is that in 1999, the lesions were twice as-- grew twice as fast in the summer as in the winter. They essentially stopped growing in the winter.
But we've had consistent winter warming through this whole period, and so these temperature sensitive infections on corals have been getting faster and faster through time. And the winter growth rates have caught up. So these never die back, they're basically killing the coral. So this is a little bit of detail about how this temperature effect can operate. And that's only till 2006, but Ernesto just sent me yesterday the data all through 2011. So you can see that the warming has continued and the rates of disease-- yeah?
AUDIENCE: Why do they become susceptible to disease that they lose their algae symbionts, and how do they keep living if they lose the symbionts, which I assume provide photosynthesis and therefore nutrients?
DREW HARVELL: Right. So the symbionts, they're obligate in the sense that they need to have this algae in their tissue. They're basically-- they're solar powered animals, is what a coral is. They can live for short periods without the symbionts. They won't grow, but they can live. And then they can reacquire them from the water column. And so that's how they can survive.
AUDIENCE: But they're more susceptible to disease without them?
DREW HARVELL: Well, it's--
AUDIENCE: Or are they just less healthy?
DREW HARVELL: Well, we think they're more susceptible to disease. There's a lot of research actually trying to investigate the complex-- the immune system between the coral and the algae to understand how they become more susceptible. It's tough because it's really a double whammy in a warming event, because not only does the host become stressed and more susceptible, kind of like college students at exam time, but also the pathogens are growing more faster.
So that's really the key to why a warmer world can be a sticker world. A lot of pathogens, the microorganisms, the bacteria, and the viruses cause disease can be below their optimal temperature. So when you warm things up, they really, they do better. So you have two things operating. It's a great question.
This isn't just the Caribbean. This is Southeast Asia. I'm not going to go into much detail, but these are bleached corals from a reef in Thailand in 2011. And these events are becoming almost annual, somewhere on the globe. Way back when, I was a graduate student, we didn't even know about coral bleaching. It wasn't happening at all. So this is, again, I want to emphasize this is a good example of a climate driven disease phenomenon.
Now the project that Laura and I worked together on was to do some modeling and projecting associated with climate change and disease. Our part of that was predicting outbreaks of a climate driven coral disease in the Great Barrier Reef, and laying the groundwork to also do this in the Caribbean. And so this is sort of one of the things we can do is be prepared for these events.
Seems like it's worth-- Laura said, be sure you tell them why we should care about coral reefs. There's a lot of reasons. Several other projects that I work on in Indonesia, in the Philippines, in East Africa, are funded by the World Bank. And that's because the economies of those countries are critically dependent upon their coral reefs, because of a range of what we call ecosystem services.
Certainly they are the richest areas-- habitats for biodiversity in the ocean. They're a rich source of fisheries, ecotourism dollars, wave breaks. And we've even done some research on pharmaceuticals from coral reefs. They're one of the regions that has the highest hit rates in terms of discovery for new, important pharmaceuticals. So they're valuable habitats.
OK, I'm going to move on. I want to just give you two other brief examples related with climate impacts on disease in the ocean, just to make the point this is much more general than just coral reefs. I don't know if anybody saw this, ocean acidification linked with larval oyster failure. Like temperature, the other factor that's driven by climate in the oceans is carbon dioxide accumulation, which is called ocean acidification. Has anybody heard of this? Yeah. So what do you think our levels of CO2 are now, our greenhouse gas accumulation? Does anybody happen to have that figure right at hand?
AUDIENCE: Is it 390?
DREW HARVELL: Very close. Let's call it 390. That's parts per million CO2. So a quarter of that CO2 will be absorbed by the oceans. So if we didn't have oceans, we'd have a lot more problems with greenhouse gases. However, that CO2 causes problems in the ocean. It's causing a direct effect, which is acidification. And the acidification isn't uniform everywhere. It's much higher in the Pacific Northwest, where there's upwelling that contributes to it.
And already this year, and last year, and the year before, there were large scale problems in the oyster hatcheries associated with acidified water. That water was corrosive enough to prevent the oysters from metamorphosing, and there were large scale die offs. There's also a bacterium associated in that area that likes acidic waters, and so it caused a disease outbreak in the oysters.
So these are events that are happening now, this is near term. This is occurring already. And then also associated with warming, there are various pathogens, such as this oyster pathogen that's expanding its range up the east coast. So there's a lot of movement of organisms in the ocean, and disease organisms are among them.
So I want to end my section, and I'm hoping that you'll have questions for us afterwards. I've talked about my three examples of rising tide of ocean diseases, and Laura's going to take over for the next part.
LAURA HARRINGTON: How many people here have heard of the Asian tiger mosquito? OK. Sometimes when I ask my students, the ones from the mid-Atlantic states have definitely heard of it, because it's really taken over in that region. And it's heading this way. And I'm highlighting the Asian tiger mosquito because not only is it an invasive species, it's a species that was introduced to the US in the mid '80s, probably in tires. It can lay its eggs inside containers, and they can remain dry and dormant for some time, and they can be dispersed readily that way.
So I'm highlighting it as an invasive species, but also many of the pathogens that it transmits are also invasive. And one example that I'll tell you more about today is chikungunya. So Drew has already told you about the effects of warming, which is part of climate change, on oceans and disease. And in the same way, warming effects mosquitoes and the pathogens that they transmit.
So for example, temperature drives the development of not only the mosquitoes that do what we call vector transmit pathogens, but it also drives the development of the pathogens within the mosquito vector. Warming temperatures can also, especially in the winter, which we've already observed, can increase the survival of mosquitoes that over-winter.
So this particular species over-winters in the egg stage, and it can survive, as the winter temperatures get warmer, in containers, even under the snow, as long as the extreme cold temperatures don't dip below the standard traditional levels. Another effect of climate change is extreme rainfall. And mosquitoes spend part of their life in water. Water is essential for them to complete their life cycle, and increases in water-- in rainfall can increase the availability of breeding sites.
So I'm going to talk about chikungunya virus today. How many people have heard about chikungunya before today? Sometimes when I ask my students they think it's something on the local Chinese menu or something like that. The name sounds unusual. It's actually from the Makonde language, which is a Tanzanian tribe. This is where we think the virus originated, in Africa. And-- around the Rift Valley region. And it means, that which it bends up, or bent up in pain. And that's a classic symptom for humans who are infected with chikungunya.
This is a virus. It's-- it has been around for some time. It was first detected in the 1930s. But in recent years it's changed. And it's shown a surprising ability to expand geographically. And one of things that has happened is that the virus has mutated, so there's a new form of the virus. And this new form of the virus actually can more readily invade the Asian tiger mosquito, and replicate within the Asian tiger mosquito. So that's why we're concerned about this duo. The Asian tiger mosquito, which is invasive, and also this virus.
So on the back of the Asian tiger mosquito, chikungunya virus has spread out of Africa into the Indian Ocean, into India, and now into Europe. And there was even local transmission of chikungunya in temperate regions of Italy a few years ago. Another thing about this new genotype of the virus is that where traditional chikungunya infection was what we call self-limiting, or people recovered from it, and it was rarely fatal, this new genotype has some mortality. It's still low, it's still less than 1%, but it is causing concern, and we don't know if mortality rates will increase over time. And there's no vaccine and there's no treatment. Like many of these mosquito borne viruses, just like dengue, like West Nile, there's no vaccine, and so treatment is really supportive.
So there are a variety of different symptoms with chikungunya. There's always a fever. There's nearly always a rash associated with it. Probably one of the key symptoms is pain in the joints. It's a little bit different from dengue, where you have pain in the back, larger bones in the body. Usually with chikungunya you have pain in the fingers, in the elbows, in the ankles. You can have swelling, arthritis can be associated with it.
And for some individuals this can be long lasting. So this is something that I hear over and over again from chikungunya patients, is that they were sick for months, sometimes years, with debilitating symptoms. So even though the mortality rate isn't as high as for some other viruses, the impact on human well being is significant.
OK so this map shows the movement of different strains of chikungunya out of Africa. And I want to highlight the strain in blue here, which moved into Reunion Island. There was an outbreak in 2005 in Reunion Island. And from there, travelers actually went back to Europe and brought chikungunya back to Europe. There was movement also into India. The outbreak in Italy that I mentioned was from a traveler, an Italian traveler, who went to India and returned in the summertime to his community, and the Asian tiger mosquito was there and it started and epidemic.
So we're really concerned about these introduced, these invasive mosquito species. We have several in the United States. The yellow fever mosquito has been around a long time, it was probably brought over with the African slaves to the New World. But some of these other species are relatively new. The Asian Bush mosquitoes was discovered in New Jersey and Long Island simultaneously in 1998. And the Asian tiger mosquito was introduced in the mid '80s.
This map shows the global expansion of the species. It's amazing. This is a very quickly developing mosquito. It tends to be very competitive with other mosquito species. In red shows the places where it's been introduced and become established globally. It originated in Asia, and it's really moved around the world and is still expanding in its range.
So what are we doing about this issue at Cornell? Well, we have a couple of studies that are ongoing. One of them is the study in collaboration with Drew, where we did some modeling to try to understand the risk for human health here in the US, with the chikungunya introduction. The other study that I have conducted is a study to understand if local US strains of the Asian tiger mosquito can actually transmit chikungunya. And so I did this work with colleagues at Colorado State University. you need a highly contained facility in order to do this work. And I'll tell you a little bit more about these two studies.
So with the testing of the US strains of the Asian tiger mosquito, we took strains from the New York-- so the Asian tiger mosquito is established on Long Island now. It has been detected in New York. We've collected it in Central Park several years ago. It's well established in New Jersey. So we think, as temperatures increase, it will move and become well established in New York. So what we did is we took one of these Long Island, New Jersey strains and we tested it against this epidemic strain of chikungunya that I told you about. And what we found is 80% of these mosquitoes were able to take up the virus in a blood meal and then transmit it.
And we compared this to the Asian tiger mosquito from your Reunion Island as our comparison, and it was just as competent as those mosquitoes that were involved in the outbreak on Reunion Island. So indeed, I think that we-- this study really gave us some good information about the potential for transmission by our local strains.
The other project that we conducted was a modeling study, and this is in review now in [INAUDIBLE] neglected tropical diseases. And what we did is we looked at the potential for introduction of chik to three different areas in the United States. The model was driven by temperature as well as other environmental factors, and included human movement patterns. So we actually looked at commuter movement in these different cities to try to understand the spread of the virus.
So the New York Metro area was one of locations that we picked. And what we found from the study is that areas of seasonal transmission, where you have distinct winter and summer, like New York, you can have the potential for an outbreak of chikungunya by one individual coming into the area. What we learned also from-- or what we estimated from our modeling study is that by using vector control, well planned, remember there's no vaccine and no treatment, you could actually interrupt an outbreak in this area. Some of the other regions we looked at farther south, it would take more than vector control to actually interrupt an epidemic.
So these are just some of the modeling outputs that I wanted to show you. This one is the probability of an outbreak. Here we have New York, Atlanta and Miami. And what we found is that the probability of a full scale outbreak in New York reached 38% later in the summer season. So if we have an individual coming into the city who is what we call viremic, they have the virus circulating in their bloodstream, a mosquito can pick it up in a blood meal. The risk begins in July and it peaks in August. And the later in the summer we go, the higher the risk; eventually it starts to die down in the fall.
And what we did is, in our models, we assumed a fairly high mosquito to human ratio. We had about five mosquitoes per one individual, which is high, it's much higher than what we have in this region. So I wanted to mention that, that this is a prediction of what could happen in the future with these human to vector ratios.
This model output is for the peak infection rate. And this varied also significantly, so part of our modeling exercise was to try to understand what different factors are important in influencing an outbreak. And of course depending on the ratio of mosquitoes to humans, the proportion of mosquitoes to actually feed on humans rather than dogs or some other animal that they can't pick the virus up from, we get different outputs. Question?
AUDIENCE: This slide makes me realize I might have misunderstood the earlier slide. You said that 80% of the New York, New Jersey [INAUDIBLE] mosquitos are currently carrying the virus?
LAURA HARRINGTON: No, no.
LAURA HARRINGTON: Yes. 80% of the ones we tested were able to pick up the virus in a blood meal and then transmit it. So we actually had them salivate--
AUDIENCE: [INAUDIBLE] blood with the virus, as it were?
LAURA HARRINGTON: Yes, we fed them blood with the virus. And then the way we test that is the virus gets into the salivary glands of the mosquito, and they salivate when they take a blood meal. So we actually had them salivate into a medium in a tube, and then we tested that for virus. Yeah.
AUDIENCE: And when you say the [INAUDIBLE] infection rate, is that the 38%?
LAURA HARRINGTON: 38%, yeah.
AUDIENCE: So if there was an outbreak, we're saying that 38% of the people in New York could be affected.
LAURA HARRINGTON: No. So there's a 38% probability that one individual coming in to New York infected with the virus would start an outbreak. Is that clear? So there's-- so it's not 100%, because you can have perhaps no Asian tiger mosquitoes feeding on them. They might not be exposed. There are other factors that come into play.
AUDIENCE: How are you defining outbreak?
LAURA HARRINGTON: An outbreak is the-- it's more than one individual from the index case contracting the virus. That's a really good question.
AUDIENCE: That would imply that if there were ten people with the virus in their blood coming into an area and they went outside a lot, that there would be an outbreak.
LAURA HARRINGTON: The probability goes up, absolutely. You're right. That's why we feel that it's conservative because we're just looking at one individual. But yes, you get a group of people coming back from a tour, or just traveling, the probability goes up.
AUDIENCE: And do you have any sense of how well-prepared either public health agencies or individual doctors are to recognize this as opposed to all the other things that--
LAURA HARRINGTON: That's a really great question. I wanted to tell you more about that. I don't think we are prepared. And that's one of the reasons we're here today. We really want to raise awareness about this. So I'll tell you a little bit more. There's some guidelines that have been published, and I'm hoping that public health officials and physicians in New York will take notice of that. OK. Drew?
DREW HARVELL: Laura, so in terms of your model, you have New York, and Atlanta. Is the notion that with climate change that window in New York will widen?
LAURA HARRINGTON: Absolutely.
DREW HARVELL: And it will start to look more like [INAUDIBLE].
LAURA HARRINGTON: Absolutely. I'm glad you mentioned that.
DREW HARVELL: --climate change.
LAURA HARRINGTON: So this is right now. And we know the temperatures are just going to increase. We know that the population of the Asian tiger mosquito is just going to increase. So it will only get wider and wider. At some point, to the point-- this is Miami over here, where you just have so much transmission, the mosquito populations are so high, that you just have continual transmission throughout the season.
AUDIENCE: So if we're saying that there's a 38% probability that one individual infected with the virus could start an outbreak in New York, how does that compare with percentage probabilities in the other--
LAURA HARRINGTON: They're higher in the other locations, just because the vector population is higher there. And also because the temperatures are higher. So hopefully that gives you a sense of how critically important temperature is in driving this entire system. Question.
AUDIENCE: In terms of the readiness of public health officials and doctors, is this do you think the most likely tropical disease that could cause an outbreak, or this is just one of many that you chose as a--
LAURA HARRINGTON: Yeah, this is just one of many. I think that it's very likely, based on what's happening in Europe. So we've already seen this happen in Europe under very similar environmental situations, like the Italy case that I was telling you about. So we picked this because it was a new virus that we thought was really poised to come into the US.
We are susceptible to dengue here. This Asian tiger mosquito transmits dengue. We already have dengue within our borders. We're dealing with increases of dengue in the southern states.
Some of the other viruses we were talking about earlier before the session started-- Rift Valley fever. This mosquito also transmits Rift Valley fever. We're talking about up to 60% mortality rate in humans. So there are some very serious viruses out there. This is a model. But I think the lessons that are learned and the plans that are developed for this model could be applied to these other infections as well.
AUDIENCE: When you say it's very likely, is it possible that it could happen this summer? Is there anything stopping it happening this summer?
LAURA HARRINGTON: I don't think so. We have to put this in perspective. For New York City, the populations of the Asian tiger mosquito are not as high as what we used in our model. Remember I said we had five mosquitoes for every one person. Right now, there are five mosquitoes for every one person in Atlanta for sure, and some of the other locations. So it may not be New York. It could be some of these other locations.
But the thing about New York, as you know, it's a major port of entry to the US. From people who are coming from places where chikungunya is endemic. And so in some cases that might increase the risk of introduction here.
It's hard to predict anything, and it may not be introduced here this year. Or it may not be detected. For example, with West Nile virus, it's likely it was introduced before it was detected. But we should be aware of it for sure.
I was talking with someone earlier about this. We didn't learn our lesson from West Nile very well. And a lot of health departments around the country don't even have the reagents to detect chikungunya. And that was the problem with West Nile. And so I think we should really be thinking about lessons learned from prior experience, and New York was a major example.
AUDIENCE: How did the peak probability of the virus transmission causing outbreak-- what is that in Atlanta and Miami?
LAURA HARRINGTON: It's much higher. Well, I guess it reaches a peak that's the same, but the window is much broader. So, for example, in Atlanta we're talking about introductions in May, any time between May and November, the probability being about 40%. In Miami, any time of year you've got a 45% probability, based on our model parameters, which may not be optimal. That 5 to 1 ratio, for example, is one parameter.
AUDIENCE: And you used that same 5 to 1 model in all of research?
LAURA HARRINGTON: We did.
AUDIENCE: Other than the satisfaction of knowing what it was, why would it benefit the public health department in Atlanta or New York City to know that the patients they were seeing had chikungunya virus?
LAURA HARRINGTON: Because it's a debilitating illness.
AUDIENCE: Right, but they can't treat it.
LAURA HARRINGTON: They can't treat it. They can provide supportive care, and they can stop other people from getting sick. So they can implement public health interventions right away, which means isolating the patients so they can't be fed on by mosquitoes and getting out education messages, and that sort of thing Great question.
AUDIENCE: One more question.
LAURA HARRINGTON: One more? So I just wanted to highlight-- so this document is a plan that was published last month by the CDC in the Pan American Health Organization. And I really wanted you to know about it. It's a good document because it has all the information about chikungunya. It has case definitions for physicians. It talks about the vector. It's good as far as providing recommendations, but they're fairly general recommendations.
The other thing that this document highlights this is the number of cases. So 126 lab confirmed or probable cases of chik have been detected from people coming back from traveling into the US. So people are coming back infected with this virus already. And the general recommendations are to develop a plan, to start thinking about it. So different metropolitan areas, states, counties should be thinking about this and coming up with a plan.
What to do? Again, there's no vaccine or treatment, so vector control is really critical. And based on what we know about the Asian tiger mosquito, there are some things we can do.
We know that we can treat within a short area around the index cases, for example, because the mosquitoes don't move very far. We know that we can look at the movement patterns, the commuting patterns, of individuals and start to predict where they might have been exposed to mosquitoes. So there are things that can be done. And also informing the public-- letting physicians know that they should be looking for signs and symptoms of chikungunya illness.
So this could be a really helpful guide for developing a response plan. Question?
AUDIENCE: The city of New York Health Department's got a document. They look like they produce it every year about mosquitoes in general. What are your thoughts on that and do they need something more specific about this virus?
LAURA HARRINGTON: Yeah. I haven't seen the one that they put out for this year yet, to be honest. But I don't think it hurts. It tends to be quite general and focused on West Nile virus. And I think that there would be a benefit to including at least signs and symptoms of chikungunya. And don't forget about the physicians, the primary care providers, too. It's really important that they are educated about this as well.
Hopefully today Drew and I have given you some more updated information on the issue of climate change. Hopefully you can see these linkages. They may seem like different systems, the corals and the mosquitoes, but they're actually all interconnected. And when we started our project together, we were thinking about how we could link everything together. And it just naturally came out.
So the same sort of modeling exercises, the same sort of detection systems, risk estimates that you'd use for the coral disease, you would use at least to start with the vector borne diseases. And it really reminds us that this is all connected and within this global ecosystem. We call it one health, where animal, human, and environmental health is all interconnected together. And I think we can open it up for questions.
AUDIENCE: I'm curious what it is about the Asian Tiger mosquito that makes it capable of transmitting a virus [INAUDIBLE]?
LAURA HARRINGTON: That's a wonderful question. I wish we knew that. I think there are scientists who've been devoting their careers in trying to understand that. For some reason, the Asian tiger mosquitoes is just a good, all around vector. I tell my students it's probably the best all around mosquito vector there is.
We know of 22 different pathogens that it can transmit well. Some of them are viruses that affect human health. Some of them affect animals. The dog heartworm, for example. It's a very good vector of dog heartworm. And we don't know why it's so permissive to infection. That's the billion dollar question I guess.
AUDIENCE: I have a few more questions about chikungunya. You said that one of the ways to control the vector would be to identify people who were infected. It sounds like some kind of quarantine, but if this is a disease that can last for years in the body, is that something that's being proposed? How long would that quarantine--
LAURA HARRINGTON: So what happens is when somebody gets infected, it takes a while for the virus to build up and replicate in their body. At some point in time, they enter what we call the viremic window. And so they have virus circulating at high levels in their bloodstream.
And that's what we're concerned about for mosquitoes. If they feed on that individual during that viremic phase, then the mosquito can pick up the virus. That phase only lasts about a week. And so after that, even though the individual is still ill, they can't be infectious to mosquitoes. So if you talked about isolating patients, it would not be for long term. It would only be for a shorter period.
AUDIENCE: [INAUDIBLE] Is this one that young children and the elderly are more susceptible or does it kind of cross--
LAURA HARRINGTON: Yeah, the elderly are the most susceptible to this virus, but young children are as well. And people with weakened immune systems. It's the same sort of epidemiology as with West Nile virus. Another question?
AUDIENCE: Is it transmittable between people or does it need to go through the mosquito?
LAURA HARRINGTON: Now, that's a great question, and that's something to think about for planning. We do not believe that it's transmissible from animal to animal. But again, we were surprised with West Nile. We didn't know that it could get into the blood supply. And there were many cases of people contracting West Nile from blood transfusion, organ transplant. There were cases of transplacental transmission of West Nile. I don't think enough research has been done on this virus to know that for sure. But I think that the likelihood would be low, but it can't be ruled out.
AUDIENCE: Most of the things that mosquitoes take up don't benefit them at all, and some of them, in fact, are quite deleterious to the mosquito's health. Is the fact that this mosquito is so permissive, do chikungunya infections of the mosquito hurt it and has that been looked at as a way of trying to modify the mosquito?
LAURA HARRINGTON: So another great question. I don't think anybody has really good data on the impact of these viruses on the fitness of the mosquito. Certainly we know with some of the parasitic infections, once the parasite burden gets really high then it affects the fitness of the mosquito. A lot of these viruses really have co-evolved with the mosquito vector. And so they're actually very well adapted to minimize the impact on the vector in order to maximize their own fitness.
So your question was does this impact the fitness of the Asian tiger mosquito, right?
AUDIENCE: Well, people have worked on things like malaria to see if they could make the mosquito resistant to the microorganism. I guess no one understands the Asian Tiger mosquito well enough to think of a way of making it resistant to taking up the virus.
LAURA HARRINGTON: So I have a little bit of experience with that with dengue. So I was involved in a project to make a dengue resistant mosquito. That's a virus like chikungunya. It's a different type of virus, but a similar issue. We do know that there are certain receptors in the gut that bind with the virus that allow the virus to enter the mosquito. And you can actually knock out the genes that create those proteins. So you can genetically modify vectors. It does affect their fitness sometimes.
But the biggest problem is how to get-- well, there are many problems. There is the ethical problem of releasing transgenic mosquitoes in the population, which is really big issue and an important one. But there's also the issue of how to get these certain genotypes into the population in high frequency so that it's actually protective. And that's a very difficult technical problem that hasn't been overcome to date. So genetically modified mosquitoes, where you're really targeting the interaction of the parasite where the pathogen with the mosquito has not really been accomplished at an operational level.
Other approaches have been tried. One of them is using a bacterium, which lives in the mosquito and makes them sterile. So there's a project in Australia where they've done field releases with that. So that's sort of a sterile mosquito program. We try to reduce the population of mosquitoes rather than replacing the population with a genotype that can't transmit. So I think we're still years behind kind of making any progress in that area. I think really the effort should go into vaccine development for these pathogens.
AUDIENCE: Is there any?
LAURA HARRINGTON: There are experimental vaccines. Actually, there's a West Nile vaccine in development. For chikungunya there's no commercially available vaccine, but there are some experimental vaccines. And because of the importance now of chikungyna, I think efforts will move forward to develop a vaccine. But it can take years to get these vaccines to market, and they might not be effective.
AUDIENCE: You said the health effects of chikungunya can last up to a year or more?
LAURA HARRINGTON: Sometimes more.
AUDIENCE: Has the disease been around long enough that they've studied long-term implications of what the impact has longer than that?
LAURA HARRINGTON: Yeah. It's been around long enough, but surprisingly, to my knowledge, I've not seen some really carefully controlled, well conducted studies on long term impacts of chikungunya. You really have to track patients through time. And that can be a difficult thing to do.
AUDIENCE: Highest concentration states would be in Africa I'm assuming?
LAURA HARRINGTON: [INAUDIBLE] India. Actually, India has a lot of cases. There are some really good studies going on now with the Reunion Island population. A very high proportion of that population was infected with chikungunya, so there are lots of asymptomatic cases. And I think probably the best information will come out of that population because people are tracking them through time. And if you look in the literature, there are lots of really good studies coming out of that population.
AUDIENCE: I'm curious regarding this virus or just generally with vector born human disease or with corals, is there a threshold we're looking at with regard to climate change in terms of temperature?
LAURA HARRINGTON: Do you want to address that?
DREW HARVELL: The bleaching occurs just above 30 degrees. So we know pretty much what the thresholds for that physiological response are. And for some of the diseases, it's been worked out that one or two degrees in excess of that will trigger outbreaks. But it's an evolving front as well, so it's changing through time. And I don't know with the human outbreaks what the thresholds would be.
LAURA HARRINGTON: So the coral disease work is so much farther along, or advanced, than the work with the vectors. I think what will be interesting is that there probably will be shifts in where these infections are endemic. So there won't necessarily be a threshold.
There is an upper limit in temperature for optimal survival of the vectors, which effectively will interrupt transmission. And so when that happens you'll probably start to see shifts in where the location of where these infections are endemic. Does that answer your question? So once you get up-- well, each mosquito is different. But for the Asian Tiger mosquito, when we start talking about sustained temperatures of 40 degrees or more, it could negatively impact survival.
AUDIENCE: You mean 40 C?
LAURA HARRINGTON: Yeah. 40 C. Sorry. I don't know if it's as much a question of threshold as the risk is going to go up and up and up until it just gets too hot for the vectors, and then you'll see the shifting patterns farther north.
AUDIENCE: So maybe in areas in the tropics, this disease will disappear because it's--
DREW HARVELL: Right. So there's an optimum temperature, and when you're below that, a further increase in warming will trigger an outbreak or allow it to occur. There's other examples. For example, new diseases of salmon in the Yukon with warming of the rivers there has been causing some outbreaks. And I don't know exactly what the temperature threshold is, but there definitely are thresholds that are definable for a lot of these.
AUDIENCE: So there's coral bleaching, but have you seen any evidence of coral migrations? Are there new sites where coral is now becoming--
DREW HARVELL: There are. That's such a good question. So, for example, we've noticed around Florida, coming up the coast, some of the coral populations are beginning to recruit a little bit farther north during warm years. And certainly in Australia, where there's a very wide latitudinal range for corals, there's been a detection of a widening of that range to the north and south. And if it were only warming for coral reefs, we'd expect there to be a lot of extinctions but that we might be able to maintain the integrity of reefs.
The problem is this acidification issue that I mentioned for the oysters is also a huge problem for corals. So it's already been detected that coral skeletons are thinner. So one of the tipping points with acidification is the ability to make a calcium carbonate skeleton. And those corrosive waters make it harder for organisms like snails, oysters, corals to actually make their calcium carbonate skeletons.
And so you could imagine the corals might expand their range if it were only temperature. They could go to cooler places. But in the next 50 years the acidification is going to catch up with them, so there will be no place to hide from that. So that's kind of a big problem we're concerned about in the ocean.
AUDIENCE: In that New York City public health document, it talks about the first case of the virus in the city in 1997. Do you know where that person had been?
LAURA HARRINGTON: The first case of chikungunya? I don't know where that person had been. I do know that there were quite a few cases coming in India, from travel in India. It's quite possible that that person was coming from there.
AUDIENCE: If the most important food source from the ocean were jellyfish, we'd be very happy now. They seem to be benefiting from acidification and global warming and thriving in new environments all over the place. Besides jellyfish is any other type of organism expanding its range thanks to these changes.
DREW HARVELL: That's a good point. Actually Jeremy Jackson, I think, titled one of his papers "A Slippery Slope to Slime" because of the predicted prevalence of groups like the jellyfish with warming and acidification. Some of the phytoplankton and the algae really like it. They like the increased levels of CO2. We can go to natural seeps in the ocean where there are already very high levels of CO2 and figure out what it is that lives there to get a vision of what our future might be like in the ocean.
There's a couple places where we've done those diversity grades where you go from a vibrant coral reef to these CO2 seeps. There's one in Papau New Guinea. And in general, the diversity falls off very fast. You find far fewer species that are able to live there. You find it tends to be more things like plants and maybe some jellyfish, but certainly not calcified organisms.
AUDIENCE: I have a question about the coral. Just to be clear, you said that the bleaching is caused because the symbiotic algae in the coral are dying. There's all these ideas of humans trying to reverse the effects of climate change that we've cost. Is there any project to try to re-engineer the algae or somehow help with that, like a vaccine for corals?
DREW HARVELL: That's a really good question. There's a incredibly interesting back story about those algae because there are a lot of different genetic variants of the algae. And they don't actually die. What happens is they bail out. So when it starts to get warmer the algae-- the ones that were in the tissue-- leave and different genetic stocks can come in that have a higher thermal threshold. So it is a possible mechanism of adaptation.
And there has been some interest in looking at some of the thermally tolerant clades of those algae to see if we could engineer them into the coral so that they would have a better thermal tolerance. So far it hasn't actually been successful because some of the clades that we've looked at, the corals don't grow as fast. The thermally tolerant clades, you put those in the coral, the coral doesn't grow as fast or re-produce as much. It's not a perfectly good algae.
But there's certain potential there, and there's a lot of interest in that. It's a very active area of research right now. And it's certainly something we're interested in with immune systems.
So the work in my lab is with coral immune systems, and we're interested whether there are some parts of the coral genome that could be beefed up to make them a little bit more resistant. But we're kind of a long ways from that. It's not like plant engineering with crops where we know so much more.
It's exciting work though because corals are the base of the evolutionary tree, so they're about as far from us as you can get. So it's very exciting to see that some of the same genes are active in immunity in corals as in humans. So we're learning a lot about the evolution of these complex immune systems in studying organisms as different as corals.
We've received your request
You will be notified by email when the transcript and captions are available. The process may take up to 5 business days. Please contact firstname.lastname@example.org if you have any questions about this request.
Professors Drew Harvell and Laura Harrington discuss how climate change affects human health globally and in NYC, including serious disease that could spread this summer from Kennedy Airport if conditions are right.