Tuberculosis and the cow.

Abstract

The debate about the transmission of tuberculosis from badgers to cattle, which commenced in the early 1970s, has overshadowed the study of human tuberculosis due to the bovine tubercle bacillus, the two-way transmission of the disease between humans and bovines and the role of the former as a reservoir of the disease. The causative organism of tuberculosis, variously known as consumption and phthisis, defied identification until 1882 when Robert Koch published his milestone paper ’Die Aetiologie der Tuberkulose’ in which he described its isolation from both human and bovine material. He did not give it a scientific name but simply referred to it as the ’Tuberkelbazillus’. It was named Bacillus tuberculosis by Zopf ( 188 3 ) and was given its currently valid title Mycobacterium tuberculosis by Lehmann and Neumann (1896). The generic name, meaning fungusbacterium, is an allusion to its fungus-like growth on liquid media. A few years later, an American, Theobald Smith, observed certain morphological and cultural differences between tubercle bacilli isolated from humans and cattle. He referred to these as the ’human’ and ’bovine’ varieties although he warned against the assumption that they were restricted to the hosts after which he named them (Smith, 1898). These varietal names remained in common use for over 70 years, until Karlson and Lessel (1970) proposed the taxon Mycobacterium bovis, which was included in the ’Approved Lists of Bacterial Names’ (Skerman et al, 1980). Some bacteriologists doubt the validity of this separate species and also of another tubercle bacillus, M africanum (Castets et al, 1969), considering them to be variants of M tuberculosis. Although recent studies on genomic relatedness support this view, the separate species names remain in use but they are often grouped together under the unsatisfactory term M tuberculosis complex. Soon after the discovery of the human and bovine tubercle bacilli, ’avian tubercle bacilli’ were isolated from birds and ’coldblooded tubercle bacilli’ from reptiles and amphibians. These terms are obsolete as the organisms now bear specific names. These bacilli, in common with many other mycobacterial species, are essentially environmental saprophytes whereas s