Buildings as Complex Ecosystems

If I asked you to go find an ecosystem to study, where would you look? Maybe in a forest, right? Or a swamp? Or lake? Wherever you picked, it was probably outside somewhere. When we hear the word “ecosystem”, many of us (including me) think of birds, plants and bugs.

But what ecosystem do you live in? And who’s studying it? If you’re like much of America, you spend a majority of your life indoors. We share this indoor jungle with a large number of microbes among others, but until recently few were studying the interactions in this complicated web of ventilation ducts, single-celled organisms and us. Luckily, now we have ecologist, Jessica Green. She summarizes the issue and its importance for human health succinctly in this TED Talk:


Last summer, around the same time this video was being uploaded, I had the good fortune to meet an architect at the World Health Organization named James Atkinson. Jim is a champion in the design of healthy, naturally ventilated healthcare facilities. (One of his recent achievements was the publication of the WHO guideline, “Natural Ventilation for Infection Control in Healthcare Settings,” in 2009.) Jim’s serving up the “architectural yogurt” that Dr. Green’s talking about.

This is a fascinating line of research that is just getting warmed up. I’m excited to watch how it grows in the future.

Epidemiology, I’d like you to meet Chaos Theory

I was at the International Conference on Emerging Infectious Diseases (ICEID) in Atlanta a couple of weeks ago. There were some fantastic presentations that really made me think. One speaker, Arturo Casadevall, discussed his thoughts on the role of fungal pathogens in the natural history of life on Earth. I won’t recap his whole argument, but I will say that it’s captivating and you can read more about it here. In the pursuit of his fungus story, Dr. Casadevall dropped in this little bombshell. He said that virulence is an emergent property of the host-pathogen interaction (1). Something that had been fuzzy for me suddenly came into focus. An emergent property is exactly the right way to look at it!

Virulence, for those who aren’t infectious disease people, is generally taken to mean the degree of pathology (damage) caused to the host by an organism. We tend to think of it as a property of the microbe, but it’s not. Virulence is a product of the interaction between the host and the microbe. It’s a characteristic of my relationship to the pathogen that infects me. Without me, the pathogen causes no damage. It’s non-virulent. That’s pretty cool by itself, but it’s not really big news. Even though we sometimes let ourselves slip, we really know that virulence cannot be separated from host factors, such as immune function.

But there’s more to Dr. Casadevall assertion than just that. He’s saying that the host-pathogen interaction is a chaotic system. For those of you don’t know much about chaotic systems (I would generally include myself in that category), they are dynamic systems that are highly sensitive to initial conditions (also known as the butterfly effect).

An emergent property is pattern that arises from the underlying chaotic processes. So you have a system. It’s chaotic (it’s all kinds of crazy), but suddenly emerges something that has structure (the crazy makes sense). One big example of this is life! Take me. I am a highly complex organism that is the product of chaotic evolutionary interactions at various scales (organismal, cellular, intracellular, molecular). I am an emergent property of the evolutionary process. (So are you!) It’s difficult to explain why these structures exist by looking at the inputs individually. You have to look at the system as a whole.

A few months ago, I was doing some research for an assignment evaluating the impact of HIV on the virulence of syphilis. Given that the immune response against syphilis infection is mediated by exactly the factors that AIDS depletes (CD4+ T-cells), I wondered how T. pallidum spp. Pallidum (which causes syphilis) might be evolving in AIDS patients with syphilis. In other words, if T. pallidum is under less immune pressure in those patients, could the pathogen evolve toward causing worse infection without penalty? One way to consider this question is to use math to model the interaction of the immune system and the pathogen. Researchers have begun to do just that, though not yet for the case of syphilis. Using predator-prey theory (the immune cells are the predator, the microbe is the prey), Andy Fenton at the University of Liverpool and his colleagues used modeling  to predict the effect of the immune response on pathogen competition within the host (and therefore virulence). They found that the evolution of virulence can be highly non-linear and dependent on specific immune features (2, 3).

Does this meet the technical criteria of a chaotic system? I couldn’t tell you. But it certainly seems that Dr. Casadevall and Dr. Fenton are on to something. It’s time to think beyond simple, reductionist relationships to get at what’s really going with virulence.

(1) Casadevall A, Fang FC, Pirofski L-a (2011) Microbial Virulence as an Emergent Property: Consequences and Opportunities. PLoS Pathog 7(7): e1002136. doi:10.1371/journal.ppat.1002136

(2) Fenton, A. and S.E. Perkins (2010) Applying predator-prey theory to modelling immune-mediated, within-host interspecific parasite interactions. Parasitology 137(6): p. 1027-1038.

(3) Fenton, A., J. Lello, and M.B. Bonsall (2006) Pathogen responses to host immunity: the impact of time delays and memory on the evolution of virulence. Proceedings of the Royal Society B-Biological Sciences 273(1597): p. 2083-2090.

Public health’s mixed messages

Last fall, I read “Raising Elijah” by Sandra Steingraber. This book eloquently describes the scientific evidence on the health risks of many ubiquitous industrial chemicals, particularly for children. She tells the story of scary pollutants in our water, food, and air that are propelled by strong corporate interests and remain un- or under-regulated by a government that is supposed to be protecting us.

Runaway corporations harming people and the environment with no oversight. It’s a story we all know. You can see it with a down-and-out but scrappy heroine (Erin Brokovich), in space (Avatar), or animated (The Lorax). It’s one of those “truths” that many have come to accept as the defining feature of our time. Witness the Occupy Wall Street movement. And in the case of the industries and compounds targeted by Steingraber and many others, it happens to be true.

The story is so ingrained, though, that we find it in places where it doesn’t belong. Take the anti-vaccine movement. Pharmaceutical companies are colluding with government bodies (FDA, CDC) to make money at the expense of children, right? But in this case, the classic tale just doesn’t fit the facts. Vaccines, unlike gas drilling, simply don’t command the kind of profit margins that incentivize massive corporate lobbying. (Their low cost is part of the reason public health is so in love with them.) Instead, it is the failure to vaccinate children that is harming the most people where this debate rages. Think of the thousands of infants who were sickened and 10 who died in California during 2010 due to the PREVENTABLE illness, pertussis (whooping cough). Now, I know there’s a lot more that could and has been said about this debate. It’s my not purpose to lay out the cost/benefit analysis for childhood vaccinations here.

My point is that we, in public health, are sending extremely mixed messages. When the topic is BPA in plasticware, we say, “Advocate for removal now! The government’s not protecting you!” But when asked about vaccines, our response is essentially, “Don’t worry about it. The risks are small. Trust us. For the good of society, do what we say.” And this inconsistency is fundamentally problematic. Why should the public believe us? How should an individual decide when advocacy is warranted and when it’s not? When the scientific and administrative authorities can be trusted and when they should be challenged?

The world is a confusing place for an informed consumer. Take the simple act of trying to eat or feed your child. Eating heavily processed foods isn’t good for us, nutritionists tell us. Evidence (and publicity) is accumulating to support the role of probiotic organisms in human health. Yogurt and other cultured dairy products are living foods that seem to support a healthy body flora. Unpasteurized milk, too, is a living food. But the simple fact is that consuming unpasteurized milk greatly increases your risk of contracting a severe foodborne illness.

In short, I can sympathize with the vast majority of vaccine deniers. They are using a shortcut to decide what is most likely to cause harm based on their experience with government and science. I took this same type of shortcut when I avoided YoBaby yogurt. It’s a mass-marketed food product for children. It probably has a ton of sugar, right? (Actually, it doesn’t I discovered.) The government isn’t protecting us from BPA, a vaccine denier might reason, so why should I believe they are protecting us from thimerosal? The link between BPA and endocrine disruption has not yet been rigorously proven (though science is getting there on this one), but toxicologists tell me to avoid it. So, too, the link between MMR and autism is tenuous (completely false I think we can now safely say), but shouldn’t I also avoid that? As science journalist, Seth Mnookin, pointed out this week at the International Conference for Emerging Infectious Diseases in Atlanta, most vaccine deniers are parents trying to protect their children. Although parents who elect not to vaccinate may be getting the true risks wrong by using the “government’s-not-protecting-me” shortcut, in a complicated world it’s easy to see why they do.

What’s the point of this blog?

This is my new blog about… well. About things. Things that I think mostly. Hopefully, interesting (or at least funny) things. Probably things related to my professional interests. So broadly, public health. But really, that’s not a specific enough premise for a blog. The digital world is overflowing with content. I don’t see any reason to add to the chaos unless I can offer a unique, valuable and FOCUSED contribution. Sure, there are probably about 12 people in the world who wonder, What does Jessica think about life in general? But, as much as I love you twelve, I don’t think a diary of my random musings on any topic that pops into my head is worthwhile. Does the world really need a long format publication of my Facebook status feed? (The answer is no.) So if this endeavor is going to be value-added, I think I better figure out what it is I want to talk about.

Unfortunately, that is still a work in progress. We can call this period an attempt to find my voice. Hence the blog’s current title. This is where you come in, oh 12 faithful readers. For the next few weeks/months, I’ll be adding posts here. What thread will bind them all together? So we shall see. And then, I’ll ask for your help coming up with an appropriate name.

After that, we’ll push this blog out of the nest and see if it flies. And that’s it. Voilà!

If you’re looking for my other (currently hibernating) blog, Adventures in the Confœderatio Helvetica, it has migrated to: