No course on population health would be complete without talking about how humans are interacting with nature, animals, plants, rivers, oceans, prairies in an endless and interconnected way. Thinking about all of these interconnected worlds and living on one planet has started a quiet revolution among doctors, veterinarians, ecologists, farmers, public health practitioners, who are calling for us to start thinking about One Health. Because the health of the planet and it's animals are directly related to human health. In this module, we're going to define this concept of One Health and summarize some of the relationships between humans, animals and ecosystems for zoonotic diseases, that's animal viruses that infect humans and vice versa. Then we're going to use the One Health perspective to try to identify reasons for recent increases in this zoonotic diseases. What's this One Health concept? Well, it really is about taking stock of the way in which human health influences animal health, influences health of ecosystems and vice versa. How does the health of our environment, influence the health of animals? And how does the health of animals, influence the health of humans? We have to start thinking about this kind of inextricably connected health network. When we're thinking about treating, One Health, aren't we thinking about treating all of these three important parts of our world? Candida auris is an emerging fungus that presents a really serious global health threat. The Center for Disease Control is concerned about it for three big reasons. The first, is that it's often multi-drug resistant. That means that it's resistant to multiple antifungal drugs. Second, it's difficult to identify in standard laboratory methods. It means it can be misidentified in labs without the specific technology to detect it, and misidentifications is going to lead to the wrong management of the disease. Third, it's caused outbreaks in health care setting. For this reason alone, it's really important to quickly identify this fungus in a hospitalized patient so that health care facilities can take special precautions to stop its spread. The CDC is encouraging all US laboratory staff who identify one of the Candida auris patients to notify their state and local public health authorities because this is such a serious disease. Here's a representation of how hospital infections actually arise from Candida. Well, it typically starts way back in the cycle, that human beings have put pressure on the environment and the ecosystems. Something like Candida has now evolved within wetlands to the point that animals like birds are picking it up and they actually are infected by it. Those birds and other animals that are migrating to, for instance, rural environments naturally then infect the environment there, and often it spreads to the domesticated animals within those farm settings. Well, both those animals or those people and the food that they produce work their way into urban environments. Then people that ingest the food or come in contact with this fungus, they then show up at a local hospital or clinic, and people aren't aware that they're carrying a very serious multi-drug resistant form of Candida. It spreads and more and more people get sick. There are many different emerging infectious diseases that are zoonotic. Actually about 70 percent of emerging infectious diseases are thought to be zoonotic, meaning that they get transferred from animal to human and so forth. But seven of them are ones that probably you've already heard of, things like the Pandemic Influenza A, HIV AIDS, West Nile virus, SARS, Monkeypox, Bovine Encephalopathy, and probably not, but you may have heard of Rift Valley fever. All of these are really serious diseases that are from this One Health perspective, something that we ought to be paying attention to. How might we actually look at the multiple layers in a One Health perspective? Here is a map of the mosquitoes that are infected with West Nile virus in 2003. What you can see is that there's a big concentration in Pennsylvania, and then there seems to be some more in the Central Midwest and in the lower Southwest. Okay, these mosquitoes are infected with the West Nile virus and we would think of their relationship to human beings as a potential threat for transfer. But if you look at the repository of the virus in birds, this is the wild bird surveillance in 2003, you can see that it's widespread. West Nile virus is alive and well in our wild bird populations across the vast majority of the country. Well, in 2003 it manifested in a big outbreak of human West Nile virus in the central Midwest, both upper and a little bit of the Southwest, which we probably could have predicted if we had seen the time-lapse of this infection. Because West Nile virus really started on the East Coast and then it slowly moved West. Most of us don't think about looking at West Nile virus infections in wild birds if we want to predict what's happening in humans. But indeed thinking from a One Health perspective, that's exactly what we should've done. There are a number of reasons why emerging infectious diseases are appearing more rapidly in human populations. First, human population pressure. There's about seven billion people in the world and the UN estimates that it's going to increase to about nine billion people by 2050. Human population is a major driver of new diseases because of the way in which overpopulation stresses environment. It increases proximity, so it increases the chances of spreading those diseases, and it also increases our contact with animals. We have to produce more food, there's more animal populations domestically, and as we get further and further into wild areas, our contact with wild animals also increases, even if it's not directly, it's indirectly by the way in which they're influencing the air, the water, etc. Beyond human population pressures, there's a whole host of other reasons for the emergence of zoonotic diseases. Microbial adaption, so microbes actually evolve and change genetically to their environment. When we deforest and we create, I'll call it, catastrophes within ecosystems, well, that destabilizes some of the natural balance that protects against the spread of diseases to the human world. Certainly, the exotic animal trade, and climate instability, and international travel are also increasing the frequency of exposure to some of these infectious agents. Then the last, but not least, because of its major impact is bushmeat practices. This is the killing and eating of wild animals. We know that there are major uses of bushmeat in many countries, and this is one of the primary ways in which human beings can get exposed to viruses. It was the main way, for instance, of the emergence of the HIV virus. For many decades, HIV was at the boundary of humans and animals and unable to be spread human to human. But because of this continual eating of monkeys and other bushmeat, the HIV virus actually evolved inside of human beings and inside of the wild animals, and it developed the mutations that allowed it to be spread human to human. We saw the consequences of that worldwide in the '60s and '70s. As you might imagine, the One Health perspective takes coordination across a lot of different specialties. At the global level, three global agencies are working together in a One Health way. The World Health Organization, the World Animal Health Organization, and the World Food and Agriculture Organization are all working together. The US Federal agencies that are working on One Health include ones like the CDC, the USDA, the Food and Drug Administration, the Department of Interior and Commerce, as well as the Department of Homeland Security, and the Department of Defense. All of them understand the importance of thinking about the interrelationships between humans, animals, and the environment, and how the health of one is going to influence the other. Then also, many professional societies like the American Veterinary Medical Association, or the American Medical Association, and the American Society for Microbiology are working together with the American Society of Tropical Medicine and Hygiene, and Association of Schools of Public Health all on this One Health pursuit of understanding what are the precursors and what are the risk factors, as well as what are the deterrence of health, I'll call it, consequences from one part of the world moving into the human and vice versa. We only have one planet and sometimes we forget that so many humans and animals share that same planet. When we think about population health, we really do need to consider the health of our environment and the health of the animals, wild and domestic, because we share the same air, water, soil amongst all of us.