The irrationality of being rational.

The Boyd Orr Blog is back! Hopefully with greater regularity than ever before.

Its now been over a year between posts, and it seemed like time to either put up (i.e. with my regular promises to self and other to restart the blog) or shut up – and those who were hoping for the latter, will be sorely disappointed! Many reasons for the hiatus, including the natural inertia that arises from not doing something regularly, through to the desire, as time between posts increases, to make the next one REALLY significant (a possible reason for some of the long-tailed distribution between correspondence times that has been observed in famous and ordinary people, through to realising that I was unsure about the direction that this blog should be taking – is it a personal view on science-related events, a blog meant to inform others, a blog to promote the Boyd Orr Centre, or … ? In the end I’ve decided that it perhaps doesn’t really matter too much, so long as there is some overall relevance to the scientific arena. After all, you as readers can quickly decide for yourselves if what is posted here is worth the time to read it. I would still encourage other Boyd Orr Centre members to contribute if you’ve the time – when I was blogging more regularly, there were a surprising number of views (though predictably, an awful lot of them seemed to be related to a post I did relating Star Wars Imperial Walkers to elephants).

And on to the post. Bovine TB has been in the news a lot over the last year, most recently because of a recent government strategy announcement. Badger culls have not only been continued, but rules for what is viewed as acceptable have also been relaxed. This has been supported by a seemingly innocuous statement that it is supported by the scientific evidence. Leaving aside any comment on the scientific debate itself, it is somewhat disturbing that such a blanket statement is made. Which scientists? And of course, such statements, in the face of the ongoing often vociferous debates going on in both the scientific community and in public, are a misrepresentation of the ongoing debate, refinement and synthesis that should be a defining process of science, and the scientific community itself.

Related to this, my group recently published a paper that looked at how evidence of disturbance of badger setts (from a cross-Northern Ireland survey) was related to incidence of farm breakdowns due to bovine TB. We found that (while somewhat less important than cattle herd related risk factors), a combination of sett disturbance and high badger sett density was a significant and important risk factor. In my view an interesting and useful finding, and one that broadly speaking is in line with studies in England showing that, while badger-related risk factors were important for starting outbreaks, cattle-related factors were primary factors in continuing them. It was also the subject of a rather intense peer review, which our lead author, David Wright, handled with impressive thoroughness (as he did with the entire paper – well done David). The paper received some media attention (including some good radio coverage on the Today Programme on BBC Radio 4 and on BBC Scotland) and there was also a fair bit of controversy over the use of the term ‘persecution’ to describe the unauthorised and illegal activities referred to in the paper. While in no way abrogating my responsibility as senior author for the content of the paper, I must admit that I was initially uncomfortable with this usage, however one of our co-authors insisted that this was, in fact, the standard term used for such activities, and it was on this basis that I was convinced. And indeed, it would in some ways seem to be a reasonable way to describe an activity that is both illegal and for which there is no evidence that it is even creating a positive outcome. And yet even while agreeing, I was well aware how emotive such a term really is (and perhaps, at least subconsciously, seeking out controversy). Insistence on being ‘right’ even when you are aware that it is likely to provoke a response that ends up obscuring the larger, more important debate (I don’t suppose you are reading, Richard Dawkins?) would appear to be a form of irrationality that is not exactly peculiar to scientists, but one which I suspect scientists are unusually susceptible to. Including, apparently, me.

Let the Games begin! Interdisciplinary teams and individuals in science

Just this past week saw the start of the Commonwealth Games. Hosting over 6,500 athletes from 71 countries, the Games is an enormous endeavour, and, if the first four days is anything to go by, one that will be a real success both in terms of participation and delivery of a high quality event. The opening ceremonies included an extended segment on Glasgow itself, and it would have taken a hard individual indeed not to have felt proud of the sometimes very hard history and unique character of this often maligned city.

The Commonwealth Games in Glasgow. A celebration of excellence in sport, and a spirit of common purpose across the nations of the Commonwealth.

The Commonwealth Games in Glasgow. A celebration of excellence in sport, and a spirit of common purpose across the nations of the Commonwealth.

Of course, the venues now completed, the ceremonies past, it is the sport itself that takes centre stage. Like the Olympics, the Commonwealth Games contains some team events, including hockey (field hockey to us Canadians), netball, and rugby sevens. However, by far the emphasis is on sports of the individual, and on the attainment of individual excellence. As a celebration of excellence across a collection of individuals, this of course makes it a very different kind of event compared to say, the just completed 2014 FIFA World Cup, similarly bringing together countries but in a celebration of a single sport, and in which, in the final, the best team beat the team with the best player (albeit not on his best day).

Which brings me to the science. Like sport, science is about the pursuit of excellence. Science can of course be done as a hobby, or purely for personal discovery but at its finest science is about the discovery of the new, and again like sport, the best of the new is achieved by the combination of discipline, long training and bursts of inspired creativity. Recent trends have emphasised the importance and need for multidisciplinary teams in science. Indeed, this was a key subject of the recent Boyd Orr conference, excellently led by the new co-directors of the Centre, Louise Matthews and Richard Reeve. In science which aims to solve real world health problems this is usually critical, due to the complexity of the problems we face, and rabies an excellent exemplar of this complexity, where, despite the existence of an entirely viable vaccine, surrounding issues complicate efforts to eradicate it.

Bigger and broader teams are also the emphasis of the funding bodies, both in terms of training of new scientists, and in terms of the research itself. There is of course considerable sense in removing duplication and enhancing value through partnerships, but such consortia both increase administrative burden, and inevitably lead to greater harmonisation. Can excellence be achieved by teams? Most certainly it can, and there are several palpable examples of this within the Boyd Orr Centre itself. But the hard graft of even the best teams, in sport and in science, must be punctuated by moments of individual brilliance in order to be truly outstanding – the pursuit of excellence is rarely served well by consensus alone. Perhaps the greatest trick of scientific discovery is how to listen to past evidence, and the arguments of colleagues and opponents, filtering out from this what is truly essential and not being swayed by consensus from developing a unique scientific voice. In my view, every scientist should spend his or her forty days in the wilderness – not, as in the Bible, as test of resolve in the face of temptation, but time spent apart from the multi-institutional, multi-disciplinary, multi-voiced environment to identify that voice. Finding that time is, of course, another matter.

Reservoir concepts: axioms and prepositions – Guest post by Rebecca Mancy

Haydon et al.’s (2002) “reservoirs framework” paper provides a structure for understanding reservoirs of infection by distinguishing between maintenance, source and target populations and clarifying the relationship between them (see Viana et al. 2014 Box 1, Figure I for an open access explanation). Reading it for the first time a few years ago, I found myself drawn into testing the structures and the relationships between them, generating new examples, verifying that the framework provided was sufficient to describe them, and checking whether they were topologically equivalent to those depicted in the figure. It felt like learning a new axiomatic system in mathematics. At the time, I paid very little attention to the terminology. The language of squares, circles and arrows seemed sufficient.

The Black Death, probably caused by Yersinia Pestis and depicted here on a panel of the Great Tapestry of Scotland, has long been one of the most iconic examples of a pandemic implicating a reservoir of infection and explanations of its mechanisms still attract considerable scientific interest. Photo:  Alex Hewitt/Trustees of the Great Tapestry of Scotland (GTOS)

The Black Death, probably caused by Yersinia Pestis and depicted here on a panel of the Great Tapestry of Scotland, has long been one of the most iconic examples of a pandemic implicating a reservoir of infection and explanations of its mechanisms still attract considerable scientific interest. Photo: Alex Hewitt/Trustees of the Great Tapestry of Scotland (GTOS)

Although our recent update (Viana et al., 2014) focused primarily on reviewing threads of evidence and discussing ways in which they might be woven into a tapestry to allow us to better identify reservoir systems, its writing has also led to new discussions about the framework and the structural relationships it encompasses. But it has also led to discussions of terminology. Most of these have focused on our use of the term ‘reservoir’. I’ve spent the last couple of hours trawling online dictionaries and etymological sources in order to better understand our use of the word. A foray into another of my favourite worlds: language. Understanding the different meanings of the word might also help us to understand some of the uncertainties that have been raised about the framework.

Most free online English language resources, such as Merriam-Webster and Online Etymology Dictionary, provide fairly limited information on the etymology of the word reservoir beyond a reference to its French origins. The Centre National de Ressources Textuelles et Lexicales, a CNRS resource centre, helps us to trace the term a little further back. According to the entry in their etymological dictionary, the first recorded use of the term dates back to 1510 when it was used to refer to a receptacle for holding a liquid. By 1547, it was being used more generally as a space fitted out for the conservation and storage of provisions, and by 1601 had adopted a figurative meaning, being used to refer to anything capable of serving as a repository. Despite these subtle changes, these uses all relate to the notion of a container employed for purposeful storage. Perhaps surprisingly, it was only in 1742 (in French; and slightly earlier in English according to the OED) that it took on the meaning of a place serving as a natural reserve of something. Yet among modern definitions, even if we exclude epidemiological meanings, we find a third use of the term as a supply of something in which the reservoir no longer refers to the container but to a resource that is contained. I suspect this is the sense in which Acheson employed it in explaining that Winston Churchill

“… still had his glorious sense of words drawn from the special reservoir from which Lincoln also drew, fed by Shakespeare and those Tudor critics who wrote the first Prayer Book of Edward VI and their Jacobean successors who translated the Bible.”

Dean Gooderham Acheson (1961) Of Winston Churchill in Sketches from Life of Men I Have Known.

Actually, what alerted me to the different meanings was not the etymology at all, but prepositions, something else that Churchill is reputed to have been sensitive to. What none of the above sources note is that the distinction between the different meanings of the word reservoir can be detected in its association with particular prepositions. When using it in the sense of a purposeful receptacle, we use the preposition for, such as when we refer to a ‘reservoir for heating oil’; in the sense of a natural reservoir, we would generally employ the preposition of, as we might if talking about a ‘subterranean reservoir of natural gas’. In the case where we want to emphasise the idea that a natural reservoir serves as a supply, we use both prepositions, but the meaning of the word for now changes. In the phrase ‘a subterranean reservoir of natural gas for the population of Scotland’, the word for refers not to the natural gas (as it did in the heating oil example) but to the population due to receive the gas.

In the epidemiological context, the equivalent of a reservoir of natural gas for a population would look something like

A reservoir of [infectious agent] for [target population].

And yet, the epidemiological literature is replete with examples of the equivalent of ‘a reservoir for natural gas’ (i.e. a receptacle into which one puts natural gas). A search in my Mendeley library brings up a list of examples: ‘a potential reservoir for Leishmania’, ‘a reservoir for a coronavirus’, ‘the reservoir for the origin of the SARS epidemic’, ‘a reservoir for emerging infectious diseases’, ‘a reservoir for rabies’ and ‘a reservoir for bovine tuberculosis’. When we write in this way, I am sure that we are simply being imprecise rather than implying a sense of human purpose in the maintenance of these reservoirs. But we really should try to use language a bit better than that.

But how does this distinction relate to the question of how we describe structures using the reservoir framework? Firstly, it explains why we choose to refer to the target in the definition of a reservoir. Basing our definition on that of Haydon et al. (2002), we explain that “A ‘reservoir of infection’ is defined with respect to a target population as ‘one or more epidemiologically connected populations or environments in which a pathogen can be permanently maintained and from which infection is transmitted to the target population’”. Thus, according to the framework, referring to a reservoir without reference to a target constitutes under-specification. Obviously, without maintenance there would be no reservoir; but equally, if there were no target population into which disease spills over then the term maintenance population would fully characterise the system and there would be no need to refer to a reservoir. For example, for a multi-host pathogen such as the virus causing foot-and-mouth disease, referring to buffalo as ‘the reservoir’ makes little sense because the system is under-specified: if we complete the definition by specifying a target, the factual accuracy of the statement “buffalo are the reservoir of FMDV for <target>” depends on the particular target we choose.

More precisely, the framework in Haydon et al. (2002) should be thought of as serving to describe not just reservoirs, but target-reservoir systems. According to the framework, populations and communities are classified in two ways. Firstly, according to their maintenance status as either capable of maintaining the pathogen in the long term or incapable of doing so; and secondly, according to their role in transmission between populations within the target-reservoir system as target, source, or neither. The simplest way to characterise the full system is then to view these dimensions as orthogonal: every population has an attribute from each of the two dimensions.

This construction helps to answer a number of questions that have arisen in discussion with colleagues. For example, it means we may still wish to refer to a reservoir even if the target population is capable of maintenance (or R0 in the target is greater than one). For example, this would be the case if some infections in the target came from other maintenance populations in the system. Furthermore, a source population can be maintenance or non-maintenance. Source populations that are not capable of maintaining a pathogen alone can form an essential or inessential part of a maintenance community, or simply assist in the transfer from the maintenance population to the target. In fact, all three possibilities might be involved in the transmission and persistence of the plague bacterium, Yersinia Pestis, in relation to different flea species and mammalian host communities (Eisen & Gage, 2009; Webb, Brooks, Gage, & Antolin, 2006). One might ask, as Ashford (2003) has, whether or not vectors that do not contribute to pathogen maintenance should be included in the reservoir. As Ashford notes, this particular point could be argued either way; nonetheless, distinguishing between types of vectors is important when designing interventions.

Fundamentally, there are two ways to protect the target: either we prevent maintenance, or we prevent transmission from the maintenance community to the target. As we explain in Viana et al. (2014), there are various ways to achieve these aims, which we refer to as press, pulse and block. However, this categorisation focuses on the implementation rather than the aim. For example, a pulse intervention may consist of culling (to prevent maintenance) or vaccination (to prevent transmission to the target); a block action may employ fences erected between non-target, non-maintenance populations (to prevent community-level maintenance) or between a maintenance community and the target (to prevent transmission to the target).

Simple reservoir-target systems showing the three kinds of vectors. T denotes the target population, V the vector source and P an additional population involved in the target-reservoir system. Arrows indicate transmission between populations, circles represent non-maintenance populations while squares are maintenance populations; maintenance communities are shown with a dashed outline.

Figure 1. Simple reservoir-target systems showing the three kinds of vectors. T denotes the target population, V the vector source and P an additional population involved in the target-reservoir system. Arrows indicate transmission between populations, circles represent non-maintenance populations while squares are maintenance populations; maintenance communities are shown with a dashed outline.

To come back to the importance of distinguishing between vectors that are involved in maintenance and those that are not, an interesting case arises. In Figure 1, although eliminating the vector is effective for different reasons in the three cases, the set of interventions is actually identical (eliminate population P, eliminate the vector population V, block transmission link a, block transmission link b). In the first and third case, eliminating V is effective because it breaks the transmission link to the target; in the second case, its elimination is also prevents maintenance in the community consisting of the vector V2 and population P2.

Ultimately, perhaps the most important questions about the definition and associated framework relate not to the word reservoir in the definition, but to how generally the framework applies. For example, should we use it for situations such as environmental persistence without pathogen reproduction? It seems fairly natural to apply it to when considering to parasites, but should it extend to organisms such as toxin-producing algae or fungi that do not require living matter in order to reproduce? These are all fascinating questions and it should be fun thinking about whether and how to best integrate them.

(With thanks to Daniel Haydon and Mafalda Viana for comments.)

[RRK – Comments can be made here, or addressed directly to rebecca.mancy A T]


Ashford, R. W. (2003). When Is a Reservoir Not a Reservoir? Emerging Infectious Diseases, 9(11), 1495–1496.

Eisen, R. J., & Gage, K. L. (2009). Review article Adaptive strategies of Yersinia pestis to persist during inter-epizootic and epizootic periods. Veterinary Research, 40(1), 1–14.

Haydon, D. T., Cleaveland, S., Taylor, L. H., & Laurenson, M. K. (2002). Identifying reservoirs of infection: a conceptual and practical challenge. Emerging Infectious Diseases, 8(12), 1468–73. Retrieved from

Viana, M., Mancy, R., Biek, R., Cleaveland, S., Cross, P. C., Lloyd-Smith, J. O., & Haydon, D. T. (2014). Assembling evidence for identifying reservoirs of infection. Trends in Ecology & Evolution, 29(5), 270–279. doi:10.1016/j.tree.2014.03.002

Webb, C. T., Brooks, C. P., Gage, K. L., & Antolin, M. F. (2006). Classic flea-borne transmission does not drive plague epizootics in prairie dogs. Proceedings of the National Academy of Sciences of the United States of America, 103(16), 6236–41. doi:10.1073/pnas.0510090103