9 December 2025, 4pm GMT
Simon Building, Room 2.57 [maps and travel]
Online Access tbc

Angela Cassidy, University of Exeter

From shared to separated health – and back again? The multiple lives of modern mycobacteria

Abstract

The family of microbes known as mycobacteria have undergone multiple transformations – in biological classification; connections to disease in humans and other animals; evolutionary and ecological roles; and their positioning in policy, public health, food and agricultural systems. In this paper, I will trace the multiple and changing lives of mycobacteria, with a particular – although not exclusive – focus on Mycobacterium bovis, colloquially known as the cause of ‘bovine TB’.  Building upon ideas about mess, disease framing and nonhuman agency, I will explore how mycobacteria were made visible to humans and participated in the framing and reframing of tuberculosis across human and nonhuman health.   These disease concepts have moved from pre-microbial pthisis and consumption; through Koch’s identification of ‘tubercle bacilli’ as a single cause of tuberculosis in humans and cattle in 1882; to their rapid re-classification and firm demarcation into separated concerns of human and animal health through the 20^th century; and, I argue, a recent disintegration/reintegration into the ‘MTB Complex’.   Today’s reconsiderations of mycobacteria were initially driven by the recognition in the 1970s that wild animals also carry and suffer from TB, requiring biomedical investigations to move beyond humans and domestic animals by enrolling wildlife biologists and animal protection campaigners.  These developments in turn benefited from and contributed to the rise of disease ecology in microbial science, forcing humans to engage with the ‘fundamental ontological indeterminacy’ (Atkins, 2016) of mycobacteria in farm, field and policy room.   The ongoing, unresolved knowledge controversy over bovine TB, taking place in the context of a wider resurgence of TB as a global (human) health problem meant that the newly routine (and cheap) tools of molecular biology, particularly rapid DNA sequencing were eagerly adopted by TB scientists. While these technologies have helped resolve some mycobacterial uncertainties, for example by making visible interspecies transmission routes, they have also opened up further indeterminacies, upending widely received assumptions about TB.  These include the re-classification of tubercular mycobacteria into a single ‘MTB complex’; indications that ‘animal’ mycobacteria evolved from ‘human’ forms; and the placement of these microbes into their ecological context as unruly, persistent, organisms living beyond the body in soil and water.   The increasingly obvious refusal of TB to be ‘controlled’, alongside changing scientific knowledge, has forced  tacit and explicit recognitions of the importance of nonhuman agency in addressing this chronic disease problem: initially that of ecosystems, then wildlife and more recently the agency of the microbes themselves.  I discuss the complex connections between this most recent ‘merging’ of mycobacteria across longstanding human/nonhuman divides and 21st century imperatives for ‘One Health’.  I close with a challenge for scholars of all disciplines: how can old and new insights from the separated histories of human and animal health be applied across traditional silos, and how could this this create new understandings of this very old disease?

Angela Cassidy is an Associate Professor in Science and Technology Studies at the University of Exeter. Her research expertise spans environmental/agricultural history; the history of science, technology and medicine; and science and technology studies (STS). She is interested in science-policy relations, science communication and engagement, and interdisciplinarity, and investigates these themes through a topical focus on environments, conservation and agriculture; human-animal relations; and questions of shared health. Her work explores how scientific knowledge is produced, communicated, interpreted and contested across disciplines, professions and the wider public sphere. She has explored these processes through a series of case studies, including of ‘One Health’ advocacy; food chain risks, popular evolutionary psychology, biodiversity renewal, and UK debates over bovine TB and badger culling.

All welcome!

Seminar Programme on the CHSTM Website

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