Bovine tuberculosis

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Contents

Introduction

Bovine tuberculosis is the infectious disease caused by Mycobacterium bovis.

See also Tuberculosis article.

Historical

Epidemiology

Aetiology

Mycobacterium bovis.

Clinical

Clinically, once established, bovine tuberculosis is little different from that caused by Mycobacterium tuberculosis. Most current human cases of M bovis TB in the UK probably represent reactivation of infection acquired before routine treatment of milk supplies and testing of cattle.

Humans can get pulmonary or gastrointestinal TB (caused by M bovis) from cattle; but the risks are insignificant in the UK because:

  • Few cattle are allowed to develop disease per se (and unless they do, like humans, they're not infectious). Most infected cattle are identified (and presumably destroyed) very early in the disease.
  • The level of contact with infectious cattle required for a human to become infected is extraordinary in the UK.

The rare human infections are pulmonary TB from cattle with pulmonary TB, or gastrointestinal TB from drinking milk from cows with infected udders. Both conditions seem easily recognised, so that diseased animals are likely to be destroyed before they have a chance to infect anybody.

BCG vaccination of farmers is therefore not necessary.

Symptoms

Signs

Investigations

Blood tests

Radiology

Tuberculin skin tests

A tuberculin skin test (TST) is conducted by introducing tuberculin, a protein derived from mycobacteria, into the skin. Somebody with prior immunity to mycobacteria will produce a response to test, and a vigorous response may indicate current infection with a mycobacterium, most likely (in the UK) MTB.

Until 2005 the test used in the UK was the Heaf test, which had the advantages of -

  • Ease of administration (compared to alternatives)
  • Could be read 7 days later (allowing clinics to be run weekly for adminstrative convenience).

In 2005 the Heaf test became unavailable, as it was only used in the UK, and the only company manufacturing it ceased doing so. was the only was withdrawn. The Mantoux test - the main test used internationally - was introduced instead for routine screening. This (like BCG) has to be given as an intradermal injection, which requires skill, and has to be read after 48-72 hours (up to 96 hours may be acceptable) - but certainly less than a week.

Treatment

Prevention

The disease can be prevented by vaccination with BCG vaccine, although the vaccine is far less effective than most other vaccines in current use. The risk of bovine TB is so low that vaccination against it is seldom warranted.

BCG vaccine

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