bTB or not bTB? How to control it is still the question

Guest post by Catherine O’Connor, Epidemiologist for the Health Protection Services, discussing the badger cull

As an epidemiologist, my job is to understand the how, what, when, where and whys of disease transmission. Though we now possess much fancier tools than those used by the father of epidemiology, John Snow (he of the Broad Street pump and cholera fame), it is by tackling these age-old questions that we attempt to understand and ultimately eradicate disease. But sometimes it’s not as easy as just removing a pump-handle.

For humans we have two main methods of controlling infectious diseases, either we protect the susceptible individuals or we quarantine infected individuals. Often methods are used in combination for maximum effect. For animals, we have one additional control measure in our repertoire: culling.

Culling animals is used not just to control disease (enzootic and zoonotic) but also to reduce human-animal conflicts and to ensure population survival when resources are limited. But for most, the word culling conjures up a haunting image, one of burning pyres as a result of the food and mouth disease outbreak in 2001. But culling is an effective disease control measure, in the correct circumstances.

So why haven’t we succeeded in stopping bovine tuberculosis (bTB), a disease we’ve been trying to control for nearly 90 years? I could write a book on it (or at least two chapters of my PhD thesis!). But really it boils down to this: we haven’t managed to implement the correct combination of control measures. Since the resurgence of bTB in the 1980s, attempts to control the disease in cattle has failed to stop the spread of this disease. Why? One main reason: this is now a wide-scale multi-species disease. Infection in both cattle and badgers needs to be addressed.

And here it gets tricky: while we have a reasonably effective test to determine infected cattle, no such test exists for badgers, meaning any cull of badgers is indiscriminate, targeting both healthy and sick animals. From previous badger cull trials we know that ultimately badger culling can reduce disease in cattle if executed conclusively and over a large enough area. However, if implemented incorrectly, badger culling can result in the incidence of disease increasing, which I fear is going to be the unwelcome result of the currently proposed trials in England.

There is an animal health emergency with regards bTB in England and Wales. This situation demands a proportionate response to allow the correct tools to be developed to control the disease. There is not only a requirement for monetary backing to facilitate enhanced research but also legislative support to ensure that once tools such as vaccination are developed, they can be rapidly applied. Until these exist, we will continue to fail to control this devastating disease to the detriment of both the cattle and badger populations.