Bovine tuberculosis (bTB) is an infectious disease of cattle that occurs worldwide. Its has devastating consequences for both the animals that succumb to the disease and for the personnel/farmers who care for them daily on many levels. This combination of welfare issues, production losses and the zoonotic risk to public health that has reinforced the need for an effective eradication strategy; components of which have proved extremely controversial and highlighted through a variety of media outlets. 

 



Bovine Tuberculosis

Fig.2 – The “Three-Legged Stool” approach to TB control (XL Vets, 2014).

Fig.1 – Nature (2016) captures a close encounter between the potential host (cow) and a potential infection reservoir (badger).

THE PATHOGEN

Caused by the bacteria, Mycobacterium bovis (M. bovis).
A slow-growing aerobic bacterium.
M. bovis can survive in the environment for long periods of time in a wide range of acids and alkalis. - It can survive in cattle faeces for 1-8 weeks!


TRANSMISSION

 Transmission is mainly through aerosols (infected droplets) produced by infected cattle. It is for this reason dairy cattle are at higher risk because of proximity between individuals at milking or when housed.
Reservoirs of M. bovis in wildlife species are major infection sources for cattle on grazing pasture. The main UK reservoir host being the badger (see Fig.1).
Infection may occur via ingestion of raw milk from infected cows – common routes of infection for calves and humans (OIE, 2017). With pasteurisation implemented in the 1930s, cases of bTB are now rare (XL Vets, 2017). 


CLINICAL SIGNS


Weakness, loss of appetite, weight loss, fever, hacking cough, diarrhoea and swollen lymph nodes are the classic signs; however, can take months or even years to appear.


DIAGNOSIS

Currently no gold standard.
Tuberculin test –cell mediated immunity to antigen is measured. (OIE, 2017).
Culture of bacteria takes 6-8 weeks.
PCR – takes 3 hours, but expensive!
Positive result = CULL. 


NO TREATMENT!

 There is no treatment for bTB at present and animals cannot self-cure.
If cattle test positive for bTB, Public Health England (PHE) are notified and they are to be removed for compulsory slaughter as soon as (NFU, 2013).
Farm animal restrictions on that farm are implemented until all cattle test negative for bTB.


NATIONALLY & GLOBALLY

bTB has a global prevalence and is more prevalent in parts of Asia, Africa, North America, and South America.
Significant areas of infection remain in wildlife in Canada, the UK, the US and New Zealand (OIE, 2017).
Isolates of M. bovis have been attained from many species, including: bison, sheep, goats, equids, camels, pigs, foxes, badgers, ferrets, elephants, seals, lynx and many more. (OIE, 2017). 


WHY DO WE NEED TO CONTROL bTB?

Over 30,000 cattle were slaughtered after they tested

positive for bTB! (XL Vets, 2017). Farmers then left emotionally

defeated about the loss of their stock and anxious about the

financial implications, whilst dealing with movement restrictions.
EU law requires the UK to have an accelerated bovine TB Eradication

Plan fulfilling specified criteria [Council Directive 78/52/EEC]

(BCVA, 2014). TB is spreading across the UK. During 2016, there

were 4,499 new outbreaks in Britain. (TB Free England, 2017). 



CONTROVERSIAL CONTROLS?

Regular testing of cattle and the slaughter of positive-testing

animals is compulsory at present. If cattle test positive,

movement restrictions are placed on the affected farm until the

entire whole test negative (XL Vets, 2014). Badger culling is a

highly debated topic. As the main UK reservoir for M. bovis it is

argued that controlling the reservoir may reduce infections between farms. Literature can be found arguing cases both ‘for’ and ‘against’ badger culling and it is recommended professionals should become familiar with each case.
Fig.2 demonstrates the integrative strategy currently in use to help control bTB in the UK (XL Vets, 2014). The ideology demonstrates, an integrative program will give best chances for success, however, if one aspect lacks/fails the program will be weakened. 


COULD VACCINATION BE USED?

Only bTB vaccine commercially available is “BCG” which has been used for decades. It doesn’t prevent disease establishment in animals or humans, but it does make that individual less infectious and reduces the likelihood of disease spread.
Badger vaccination aids the long-term control of the disease, but it will not cure a badger already infected (TB Free England, 2017).If cattle are intended for trade, they are prohibited from being vaccinated against bTB (XL Vets, 2014). 


References:

A.R.Spickler. 2016. Overview of Zoonoses. [ONLINE] Available at: http://www.msdvetmanual.com/public-health/zoonoses/overview-of-zoonoses. [Accessed 12 November 2017]
D.Cressey. 2016. Scientists track badger-cow encounters to understand cattle TB. [ONLINE] Available at: http://www.nature.com/news/scientists-track-badger-cow-encounters-to-understand-cattle-tb-1.20378 . [Accessed 13 November 2017]
OIE. 2017. Bovine Tuberculosis. [ONLINE] Available at: http://www.oie.int/fileadmin/Home/eng/Media_Center/docs/pdf/Disease_cards/BOVINE-TB-EN.pdf [Accessed 16 November 2017]
XL Vets. 2014. Tuberculosis. [ONLINE] Available at: http://www.xlvets.co.uk/sites/default/files/factsheet-files/TB%20Brochure%20Final%20artwork.pdf [Accessed 16 November 2017]
NFU. 2013. TB Free England: FAQs. [ONLINE] Available at: http://www.tbfreeengland.co.uk/faqs/ [Accessed 18 November 2017]
Paul Torgerson. 2014. Bovine tuberculosis: an economic threat or a big fuss about nothing? [ONLINE] Available at: https://www.bcva.eu/system/files/resources/Bovine%20tuberculosis%20an%20economic%20threat%20or%20a%20big%20fuss.pdf [Accessed 27 November 2017]
TB Free England. 2017.Bovine TB is out of control. [ONLINE] Available at: http://www.tbfreeengland.co.uk/tb-free-england/downloadable-assets/tb-infographic/ [Accessed 27 November 2017]







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