I’ve been looking for a model or framework to bring together interdisciplinary evidence on diseases of the past. There are a variety of disciplinary approaches but few that can readily incorporate very different types of evidence well.
Apart from past discussions of discrete co-morbidities, the most common framework for understanding historic disease ecology has been pathocoenosis or ‘disease pools’ originated by M. D. Grmek in 1969 and popularized as ‘disease pools’ through McNeill’s Plagues and Peoples (1976). While this concept has proven popular among historians of medicine in high level overviews of human history, the concept begins to break down when practically applied to specific problems, as outlined by Robert Sallares (2004). It is hard enough to identify all of disease-causing microbes in a modern environment, much less a historic environment or population. It is often the minor or chronic disease-causing agents that make the most difference during a co-infection; malaria being a prime contender for the most important. Pathocoenosis doesn’t adequately take into account the dynamic complexity of microbes in any population (however defined) and the idea that epidemics are disruptions in the equilibrium of pathogens in the population caused by new entrants to the population often doesn’t hold up.
Syndemics is a related concept emerging among biologists and medical anthropologists as a way to understand the diverse complex outcomes of diseases in populations. Syndemic comes from the terms synergistic and epidemic; it is a synergistic epidemic. A synergism exists when two conditions together produce a much greater effect than either individually added together ( ex. 1 +1 = 5 not 2).
A syndemic, in short, involves a set of enmeshed and mutually enhancing health problems that, working together in a context of deleterious social and physical conditions that increase vulnerability, significantly affect the overall disease status of a population (Singer, 2014).
The theory of syndemics is still evolving. The CDC’s definition refers specifically to two epidemics in the same population that produce a synergistic adverse outcome in human health. Consequently biology and medicine focus primarily on coinfections with an occasional look at nutrition. So far they are beginning to find some fascinating insights into how the immune system copes with two or more disease-causing microbes at once. We have to really take in that we are all coinfected all of the time. It comes down to if there is a significant interaction between multiple microbial species and the immune system. (It should be also said that coinfection can occasionally be protective as well.) Not surprisingly medical anthropologists insist on there always being a social component like malnutrition causing events, human behaviors like drug abuse and sexual practices, or social disorder and inequality. So far from what I’ve read, these different focuses are complementing each other pretty well.
Some of the well-recognized syndemics include:
- malaria + malnutrition
- influenza + bacterial pneumonia
- HIV + TB
- HIV + HCV
- HIV + HCV + IV drug use
- Lyme disease + other Tick Borne Diseases
- malnutrition + war (social disruption) + infectious disease (mostly diarrhea)
HIV has had a critical role in recognizing syndemics. Not unexpectedly, HIV coinfection with multiple organisms causes recognized synergetically worse outcomes. In many parts of the world, liver disease is a leading cause of HIV+ patient deaths due to Hepatitis C (HCV). It has also highlighted social conditions and behaviors that increase risk and vulnerability. The massive size, duration and amount of research done on AIDS is what has really allowed syndemic theory to become established.
Syndemics is just beginning to look at zoonotic disease but the future is already promising. As has already been suggested by work on pathocoenosis, malaria is a leading candidate to understand the syndemics of zoonoses. Syndemic effects have been suggested for malaria plus malnutrition, HIV and influenza. Patients with long-term and serious health outcomes from Lyme disease are often coinfected with other less common tick born infectious diseases that are often undiagnosed (Singer & Bulled, 2014).
From what I have read so far, syndemics appears to take the best parts of the pathocoenosis paradigm, while jettisoning the unsupportable, over-reaching baggage. As we can already see for HIV and malaria, the syndemics approach has the potential to build up a foundation to understand the multifaceted outcomes of disease causing agents in different environments and provide insights into how the human microbiome and immune system interact. While its not perfect and doesn’t incorporate all of the disciplines needed to understand historic disease, it may provide a basis to build upon.
References and further reading:
Sallares, R. (2005). Pathocoenoses ancient and modern. History and Philosophy of the Life Sciences, 27 (2): 201–220. [Malaria]
Singer, M. (2014). Pathogen-pathogen interaction.Virulence, 1(1), 10–18. doi:10.4161/viru.1.1.9933
Singer, M., & Clair, S. (2003). Syndemics and public health: reconceptualizing disease in bio-social context. Medical Anthropology Quarterly, 17(4), 423–441.
Rock, M., Buntain, B. J.,Hatfield, J. M., & HallgrImsson, B. (2009). Animal–human connections, “‘one health,’” and the syndemic approach to prevention. Social Science & Medicine (1982), 68(6), 991–995. doi:10.1016/j.socscimed.2008.12.047
Singer, M. C. (2009). Doorways in nature: Syndemics, zoonotics, and public health. A commentary on Rock, Buntain, Hatfield & Hallgrı ́msson. Social Science & Medicine (1982), 68(6), 996–999. doi:10.1016/j.socscimed.2008.12.041
Ostrach, B., & Singer, M. (2013). Syndemics of War: Malnutrition-Infectious Disease Interactions and the Unintended Health Consequences of International War Policies. Annals of Anthropological Practice, 36(2), 257–273. doi:10.1111/napa.12003
Morano, J. P., Gibson, B. A., & Altice, F. L. (2013). The Burgeoning HIV/HCV Syndemic in the Urban Northeast: HCV, HIV, and HIV/HCV Coinfection in an Urban Setting. PLoS ONE, 8(5), e64321. doi:10.1371/journal.pone.0064321.t003
Kwan, C. K., & Ernst, J. D. (2011). HIV and Tuberculosis: a Deadly Human Syndemic. Clinical Microbiology Reviews, 24(2), 351–376. doi:10.1128/CMR.00042-10
Conant, K. L., Marinelli, A., & Kaleeba, J. A. R. (2013). Dangerous liaisons: molecular basis for a syndemic relationship between Kaposi’s sarcoma and P. falciparum malaria. Frontiers in Microbiology, 4(article 35), 1–14. doi:10.3389/fmicb.2013.00035/abstract
Faure, E. (2014). Malarial pathocoenosis: beneficial and deleterious interactions between malaria and other human diseases. Frontiers in Physiology, 5. doi:10.3389/fphys.2014.00441/abstract
Herring, D. Ann, & Sattenspiel, L. (2007). Social contexts, syndemics, and infectious disease in northern Aboriginal populations. American Journal of Human Biology, 19(2), 190–202. doi:10.1002/ajhb.20618 [1918 influenza]
Singer, M., & Bulled, N. (2014). Ectoparasitic Syndemics: Polymicrobial Tick-borne Disease Interactions in a Changing Anthropogenic Landscape.Medical Anthropology Quarterly, n/a–n/a. doi:10.1111/maq.12163