Extended Interviews


Interview with Dr. Ali Khan

Dr. Ali Khan is the acting director of the National Center for Zoonotic, Vector-Borne and Enteric Diseases at the Centers for Disease Control and Prevention (CDC). In the past decade, he has led responses to numerous high-profile domestic and international public emergencies, including outbreaks of hantavirus pulmonary syndrome, Ebola hemorrhagic fever, avian influenza, Rift Valley fever, severe acute respiratory syndrome (SARS), and many more. He spoke with FRONTLINE/World’s Serene Fang about the new strategies the CDC is using to tackle emerging diseases.

FRONTLINE/World: For someone who has never heard of One Health, can you explain what it is, and what developments led the CDC to this concept?

Dr. Ali Khan: When we think of diseases such as SARS, West Nile, pandemic influenza, or even HIV [human immunodeficiency virus], one of the common factors that links these new and emerging diseases is that all of them actually started with an animal somewhere. We call these zoonotic diseases -- diseases that are transmitted from animals to humans. So this is a common theme for many of these diseases, even though, like HIV, which is one of the defining infectious diseases of our generation, or now influenza, after it originally came out from the animal world, it was then transmitted from person to person to person. 

The One Health approach asks, how do we look at new infectious diseases in animals, in humans, and in the environment to figure out how to detect them, how to prevent them, and how to prepare for them. After the germ theory, people generally thought of infectious diseases and focused on the pathogen. So people worried about the bacteria, the virus, the fungus, and so forth. And that theory was actually very beneficial -- it led to dramatic declines in infectious diseases, starting at the beginning of the 20th century. So thanks to sanitation, clean water, clean food, vaccines, and antibiotics, there was a dramatic decline in infectious diseases at the beginning of the 20th century, and many people actually said, "Okay infectious diseases are over. We don’t need to worry about them." But there are excellent examples over the last couple of decades that that’s really not true. 

"The One Health approach asks, how do we look at new infectious diseases in animals, in humans, and in the environment to figure out how to detect them, how to prevent them, and how to prepare for them."

What started to happen toward the end of the 20th century was the recognition that lots of new diseases that were cropping up -- and the best example is HIV -- originally started in animals and now are transmitted from person to person. The thing that links together some of the key infectious diseases over the last decade or two, such as HIV, SARS, Ebola, hemorrhagic fever, West Nile, and these new influenza viruses, is that they’re transmitted originally from animals to humans.

The infections due to animals represent 75 per cent of all the emerging infectious diseases; so, if you’re really going to tackle these diseases, you can’t just focus on people. You need to focus on the animals, you need to focus on the environment, and on the interface where those come together. 

If you think about the spinach outbreak that occurred in the United States a couple of years ago, traditionally, you’d say, “Okay, it’s due to a certain bacteria,” and so many people become sick and die from the disease. But if you go back and look at where the spinach is grown, all of sudden you realize that there are these feral or wild pigs carrying the same type of bacteria running through the fields. You realize that there are water issues in how these fields are irrigated, and all of a sudden you say, “Okay, if I’m looking at this not just from a human or bacterial perspective, but if I’m looking at the animals that may be involved, what’s going on in the environment -- that suggests some new strategies to try to prevent this disease.” This new strategy is really more in tune with environmental stewardship and animal stewardship in addition to taking care of people.

Is there something about zoonotic diseases, compared to nonzoonotic diseases, that makes them particularly hard to control?

Zoonotic diseases present unique challenges because they come from an animal reservoir, and these viruses exist all the time in the animal reservoir. There are a number of factors that increase the possibility for us to have contact with animals and, once we have that contact, or get infected, to spread that infection worldwide. Some of those factors include an increase in the population going into areas that are wild or where wild animals may exist, and an increasing need of that large population for agricultural products, like beef and poultry and pork.

Also, how fast people travel is really a big driver for infectious diseases. Once upon a time, it would have taken days, weeks, months to go from one continent to another. Nowadays, within 24 to 48 hours, you can travel from one place to another and still be incubating the disease, but not necessarily manifesting that you're infected. It becomes very easy to transmit diseases worldwide.

Looking back over the past couple of decades, is there a particular example of a disease or an outbreak from which you learned important lessons from a public health perspective?

SARS is really a poster child for these new emerging infectious diseases that threaten us worldwide -- and a good example of what we need to think about in the future to prevent these diseases. It was a disease that was not previously recognized, and it probably occurred from infected animals in a live market, animals that probably got infected by bats. And a transmission of the disease started within humans, through person-to-person transmission, in Southern China. 
That disease was then able to get transmitted worldwide, after it got started in humans , thanks to airline travel. And then it was transmitted within hospitals due to hospital-related factors. So this is a really good example of a new disease associated with animals that got transmitted worldwide. 

We were very lucky with SARS, in that we were able to shut down the disease with good hospital infection-control practices. But that’s not always true: The new influenza viruses are another excellent example. New influenza viruses invariably arise in some sort of animal -- usually, wild birds are the natural reservoir -- and then they either infect humans directly or through pigs. And then, at that point, they can be person-to-person and can stay endemic, or [they can be] transmitted throughout the population without the need for animals anymore. 

These examples also get to the heart of the question "How do we think about prevention?" You need to focus on the virus, but you really need to think broader. It’s not just about the virus; it’s about "OK, what are the animals that were involved, that led to this -- the factors that led to this emergence? What are the environmental factors?" And then look at that holistically to say, "What are our prevention probabilities? What are the strategies for trying to find these diseases a lot earlier than we currently do? And once we find them, how do we prevent their spread?”

So what are the strategies? How are they different from past strategies?

The One Health strategies are a lot more integrated than previous strategies. The cornerstone of our One Health strategies is integrated monitoring activities for these pathogens -- virus, bacteria, prions -- whatever they may be. When I investigate outbreaks worldwide, the animal side of the house (ministry of agriculture, ministry of wildlife) has never really spoken to the ministry of health, even though they have these diseases in common. So how do we think about monitoring for these diseases within animals, within humans, and how do we bring that information together with these integrated systems?

If you think about rabies, the solution for rabies was not going around and vaccinating everyone in the world against rabies. Here in the States, we got rid of canine rabies by focusing on the dogs. And that led to improved human health, and obviously to improved animal health. The same thing is true for other diseases, such as brucellosis, where the solution for preventing humans from getting a severe illness is not treating the person, or vaccinating the person, but taking care of the disease in animals so that you're protecting both the animal and the human.

"If you think about rabies, the solution for rabies was not going around and vaccinating everyone in the world against rabies. Here in the States, we got rid of canine rabies by focusing on the dogs."

How has the composition of the CDC team changed over the years due to the One Health strategy?

These teams have changed dramatically from just medical epidemiologists to people who are entomologists, mammalogists, demographers, modeling experts, and so forth. Our whole approach to the investigation and research studies and prevention strategies is a lot more multidisciplinary and integrated than it ever was

Uganda is also an excellent example of what we call a hot spot. In Uganda, we have been working with the Ministry of Health on diseases such as monkey pox, Ebola hemorrhagic fever, Marburg hemorrhagic fever, and plague. We're now about to send a team to Uganda to look at a novel disease called nodding disease. This is sort of a seizure-like illness in young children that may be infectious. But it's a really good example of a hot spot where diseases arise and where we should be working to try to identify what diseases are in the animals, what diseases are in the vectors, like mosquitoes, for example.

Uganda is considered a hot spot because people there come in close contact with animals  -- both wildlife and domestic -- in nature, often in an environment with the forests disappearing or other environmental changes going on. So as you bring these sorts of culture together -- the animals and the people -- it provides lots of opportunities for new viruses to emerge in that setting. The same thing is true if we think about the emergence of new influenza viruses. Those tend to emerge in Southeast Asia, where we again have this sort of confluence of people and birds and pigs all living close together, and lots of opportunities for viruses to move between those three and for a new virus to develop. So it's that combination of those factors that creates a hot spot where new diseases can emerge. 

We’ve heard that for these new, odd diseases, it's unlikely that anyone is going to invest the money for a vaccine. What are the likely strategies for reducing the disease from this angle?

For rare diseases that do not have implications in developed countries, treatment and prevention are always problematic. Often there are local solutions, if people stop thinking, “My only solution is to vaccinate somebody or have a new drug for somebody.” An excellent example of that is Nipah virus. This is an emerging infectious disease that tends to be transmitted, like many of them, by bats. In Bangladesh, it appears that the bats feed on palm dates, and the sap from the trees gets infected. They have figured out low-tech solutions, like how do we cover the pot as the sap runs down into the pot, so it doesn't get contaminated with bat or bat feces or bat saliva, and thus decrease the risk of infecting humans.

So that's just one example of many, where you're not putting all your focus on developing a new vaccine or a new drug. But you can think about “How do I, given what is locally available to me, prevent disease in the community? Is there a better way to bundle the grain or store the grains so we don't have a whole lot of rodents around?" There are often local solutions that suggest themselves if you take yourself out of the mindset that "The only solution available to me is a new vaccine or a new drug," which often will not be available for many of these diseases. 

Can you talk a little bit about how the National Center for Zoonotic Diseases was created and why a veterinarian, as opposed to an epidemiologist, was chosen to be the director?

This One Health strategy led to the creation of the National Center for Zoonotic Diseases. And the first person selected to head that center was Dr. Lonnie King, who was a veterinarian. That really was to show that if we're going to prevent disease in humans, or the key emerging infectious diseases that are threatening us, we really need to be focused on the animal side of the house. And that actually opened up a whole new set of partnerships for CDC. So we now work much more closely with the USDA [United States Department of Agriculture] than we ever had previously -- that's the animal health side of the house here in the United States -- and with animal and wildlife ministries worldwide. We have actually placed people at the World Organization for Animal Health in Europe and at the food and animal organization in Europe so that they can really help us work with this whole new community, to look at a novel set of prevention strategies for human disease.

And how recent is this development? 

That strategy has been gaining steam over the last couple of decades, but three years ago, here at the agency, we decided to reorganize around this strategy. Epidemiologists and the animal-human health folks, entomologists, mammalogists, and climate experts have all come together to say, “We're going to tackle these emerging infectious diseases with this new strategy.” This is not just here at the CDC. This is a worldwide movement.

How is this strategy playing out as far as monitoring systems go?

Currently, there are actually no good examples of integrated animal-human health laboratory monitoring systems or other disease monitoring systems that are well integrated and working with good communications. We're trying to build those. The United States has a model that looks like that, something called Arbornet, so we have an integrated system that looks at West Nile disease and other associated mosquito-borne diseases. It looks at what's going on in birds, what's going on in mosquitoes, and what's going on in people. That's the closest model we have here in the United States. We’d like to replicate those models worldwide, where the ministry of agriculture and the ministry of health, and the ministry of wildlife are working together to make sure that we're testing animals, that we're recognizing which are sick and which are not sick. Similarly, we're testing people with unexplained diseases, with fever and unexplained death to see if that could have been a new agent -- linking that information together and sharing it across agencies.

Does it ever strike you as strange to approach world health in this way?

I personally see no reason why we should make a distinction between the health of humans and the health of animals. If we're going to protect humans from emerging infectious diseases, we need to worry about the health of animals. And similarly with the wonderful example in Uganda, trying to protect these mountain gorillas. These are great examples where there really doesn’t need to be a distinction. We need to think about how we can have healthy species.