Bovine Tuberculosis – An Overview

I have closely followed the contentious issue of bovine tuberculosis management in the UK for many years. In spite of numerous eradication programs, deployed at a government level, the UK remains under threat from this costly disease. One hotly debated issue is the management of badgers, a significant wildlife host for the disease that implicates disease management in cattle. Furthermore, shortcomings in the specificity and sensitivity of current testing methods allows for uncertainty in diagnosis and can increase the risk of probability of transmission within and between herds. There are many interacting proximate factors of the disease, with underlying causes including social, monetary and practical aspects that ultimately lead to policy failure.

Bovine tuberculosis (BTb) is a serious animal health and economic problem, a notifiable disease, it continues to cause disruption to the cattle farming industry, inflicting a large financial burden on the UK taxpayer, and compromising the UK’s reputation for safe beef and dairy products. BTb is currently increasing at an annual rate of 18%, and BTb control cost the UK taxpayer around £100 million in 2011/12. This increase is in spite of numerous government BTb eradication programs, which have failed to gain control of the disease.

Over the next decade, BTb costs are estimated at £1 billion at the current disease rate and the severity of the disease is predicted to worsen, which will intensify the emotional and financial hardship on farmers and threatens the viability of beef and diary businesses. Therefore, the severity of the problem falls to a policy level, and the UK government has an urgent unresolved animal health matter.

The causative agent of BTb, Mycobacterium bovis (M.Bovis), is not exclusive to cattle and can infect a range of other domestic and wildlife mammalian hosts in the UK, including the European badger Meles meles; deer Cervus sp., Capreolus sp., Dama sp., red fox Vulpes vulpes and domestic cat Felis catus. Additionally, M.bovis is a zoonotic disease communicable to man and, therefore warrants a public health concern. However, stringent milk pasteurization, improved meat hygiene practices and human TB vaccination has led to a marked reduction in the number of human BTb cases over the past 50 years, and it is not currently considered a significant risk to public health.

The most common transmission route of M.Bovis transmission is through aerosol respiratory contamination, and a single bacillus within a nucleus droplet is sufficient to establish infection in the recipient. Other routes of transmission, such as ingestion through environmental contamination (i.e. excrement and mucus), are less effective. Although, some studies have suggested M.Bovis can survive in cool, damp conditions for up to 5 months however, those bacteria exposed to high temperatures and desiccation do not survive more than a few weeks.

The disease dynamics between hosts are still poorly understood due to the complex epidemiology of BTb, and it’s eradication is further complicated by the existence of multiple wildlife reservoirs hampering the success of long-term eradication programmes. Despite many years of research, monitoring and intervention strategies, cattle farmers and the UK government remain heavily burdened by this incessant disease.