Infection in dynamic social networks of a wild mammal

The ways in which humans transmit infections depend on the nature of the pathogen and how individuals contact one another. Some individuals, who are particularly well connected, might expect to receive and spread infection frequently, while others that are socially isolated might be expected to avoid general epidemics. In practice, human populations are usually divided into social cliques, around families, schools and workplaces, where interaction is more intense, set against a background of looser connections. Such variable patterns of interaction can be mapped into a social network, where the characteristics of individuals might relate to their risks of being infected and of being a source of infection.

Human social networks and their association with infection are quite well understood, particularly for childhood infections, such as measles, and sexually transmitted diseases, such as HIV. The same is not true of wild animals, where we still tend to think in population terms, of individuals being uniform and having simple social lives. Social networks of infection have been studied in a few wildlife species, including Tasmanian devils, meerkats and giraffes. In one or two cases, including our pilot studies of badgers, the network positions of individuals have been shown to relate to the presence of infection. However, it is hard to know which came first, the infection or the position? Did animals catch infection because they were leading risky lives, were stressed or had reduced immunity? Or were they putting their resources into reproduction instead of fighting infections and so enhancing their lifetime fitness? Did the infection itself affect their behaviour? Or did they occupy this position because they were infected, perhaps because they were ostracised by other members of their social group?

Given that many important infections of humans and livestock, such as influenza viruses, originate from wild animals, it would be useful to understand how to manage such emerging infections in wildlife. Badgers are a good example. Because they are a reservoir of bovine tuberculosis (TB), which can affect a range of mammals including cattle and humans, they are often culled in an attempt to control the disease. They are also hosts for rabies and U.K. rabies contingency plans currently provide for badgers to be culled to protect human health. The current pilot badger culls being conducted in England are a test of whether effective culling can be implemented by the farming industry, in the hope that this might control TB infection in cattle. Unexpectedly, it has been shown in earlier trials that culling badgers can also bring about increases in new cases of TB in badgers, and in cattle. This has been hypothesised to stem from a "perturbation effect", whereby culling upsets the otherwise stable social behaviour of badgers, causing them to roam, and transmit infection, more widely. Despite the prominence of the badger TB problem and widespread awareness of this "perturbation effect", we know surprisingly little about how infection is transmitted between badgers and how this is affected by culling. This project will look in detail at infection in wild animal networks, using badgers as an example, paying particular attention to social behaviour and individual condition, and working out what these mean for disease control.

We are proposing to use intensively monitored populations of wild badgers to study a range of "indicator" infections and how they relate to behaviour, stress, immune function, reproductive activity and success. Our work will give us an understanding of how infections spread, or do not spread, across real networks and will help improve understanding of the "perturbation effect". Then we will build a computer model of infections in our observed networks and use the model to test strategies to determine which is best for disease control, for badgers and TB, and for animal diseases more generally.

Bovine tuberculosis is probably the greatest challenge in animal health policy and practice in the U.K. and has a large and increasing economic and social impact. Because of the involvement of badgers, policy in this area has become fraught with difficulty and conflict among ardent stakeholder groups. It looks likely that the disease problem will continue to worsen, while conflict around badger management intensifies. Badger ecology, social behaviour and the "perturbation effect" have been shown to be critical, in both biological and policy terms, for transmission and control of TB.

More generally, a high proportion of emerging infections of humans are zoonotic in origin and so the control of infection in wildlife hosts is becoming more important to the protection of human and animal health. Therefore, while we expect this work to be of particular benefit to TB control, it will also make a significant and general contribution to wildlife disease control internationally.

Animal health officials in government departments and agencies.
Bovine TB costs British taxpayers ~£100M p.a. and resulted in the slaughter of ~37,000 cattle in GB in 2012. Control is a high priority for Ministers in Defra, Welsh Government and Northern Ireland Executive; Each of these administrations is adopting its distinct policy for disease control in cattle and wildlife. Defra is contemplating badger culling across large parts of western England. If generalised, proactive culling (as is being piloted) is not adopted, Defra ministers have identified more targeted culling, perhaps in combination with vaccination, as a potential policy option. Wales is focusing on vaccination, while in Northern Ireland, policy is focused on targeted removal or vaccination. The economic impact assessment that underpins Defra current policy, the licensing decisions made by Natural England and the statutory advice given by the Chief Veterinary Officer, all draw heavily on understanding of badger social behaviour, and perturbation in particular. Knowledge gained from this study will contribute to policy development on all these fronts because understanding of badger behaviour, perturbation and its outcomes is critical to all options for badger management.

Veterinarians, farmers, conservationists, animal welfare scientists.
Representative organisations, campaign groups and their publics.
Badger management is a topic of controversy and active social debate. Those who frame this debate frequently draw on their knowledge of badger social structure, perturbation, its effects and mitigation, but do so in a very broad and narrative way. The "perturbation effect" as a concept has achieved remarkably widespread public understanding, extending beyond academic work and permeating into popular media and public consciousness so that it underpins general knowledge of the badger-TB problem. To inform key actors in this debate, our project will help explain the importance of badger social behaviour, the perturbation effect, how it works and what its consequences are.

Disease control specialists internationally.
Globally, a high proportion of emerging infections arise from wildlife. Hence the control of the spread of infection in wild animal hosts is of key strategic relevance to protection of human and livestock health. Furthermore, infection has emerged as an important factor threatening conservation of biodiversity. Since counter-productive and counter-intuitive outcomes of wildlife control have been observed in relation to control of rabies in bats and foxes, spongiform encephalopathy in deer and swine fever in boar, amongst others, the consequences of culling for social systems and disease transmission in wildlife is likely to be manifest. By building on investigations of a well-studied system, this project will inform the direction of wildlife management for disease control more widely.