Tuberculosis in man, an animal health problem

Abstract

In testing the Onderstepoort herd of experimental animals, totalling 224 animals, 10 positive reactors were found in 1949. Since tuberculosis was eradicated from this herd in 1940 by slaughtering all reactors and doubtful reactors and since with the exception of one animal, no further cases were encountered at the annual tests during the last 9 years, this result was not only surprising, but also alarming. Seven of the reactors were from a group of gallsickness vaccine reservoir animals, which were kept in complete isolation in so far as other cattle were concerned. Their bay and bedding were sterilized. The only food which was not sterilized was the silage and the concentrate ration. Since the Onderstepoort silage was shown to contain 4 per cent. acid, it was believed that any tubercle bacilli which might be present, would be destroyed. The concentrate ration could carry viable tubercle bacilli, but even if that were the case, the source of such infection was much more likely to be human than bovine. As these animals become too old or are for some other reason no longer suitable as donors of blood for the vaccine, they are slaughtered and in every case a post mortem examination is made by a veterinarian. During the last 30 years not a single case of tuberculosis was found in this group of isolation stables. Lesions were present in six out of the seven animals. The 7th had actinomycosis, which was thought to have been responsible for the sensitization in this animal. An attempt was made to type the organisms from all six animals. In four the bovine type was identified. In one the organisms were lost and in the other, owing to difficulties in obtaining good cultures for the biological examination, the results are not yet available. It was concluded that a human being with open pulmonary lesions due to the bovine type of organism must have been responsible for the infection. All the available humans were tuberculin tested, medically examined and screened. A number of positive tuberculin reactors were found, but no clinical cases were found, on medical examination and on screening. Since the native personnel is constantly changing, it was unfortunately not possible to examine all those who were in close contact with these animals during the last two years. In another group of three positive reactors no lesions were found and it is considered that these animals were sensitized by infection with the human type of organism. The native attendant in close contact with these animals was shown to have pulmonary tuberculosis on screening, but up to now the organisms could not be identified in his sputum by direct smear examination, nor by biological examination. This experience with the Onderstepoort herd, makes it abundantly clear that man as a source of infection of the bovine with the human type of organism, with consequent sensitization and man with open pulmonary lesions due to the bovine type of organism, as a dangerous source of infection for bovines, can no longer be regarded as a rare academic curiosity, but must be faced as an important practical issue, where a serious attempt is being made to eradicate tuberculosis from cattle and to maintain them free from sensitization. Where the bovine as the source of infection has been eliminated and tuberculin tests are not carried out annually, or at the most every two years, serious and disastrous setbacks may occur, when a human being with open lesions, due to the bovine type of organism, introduces the infection to a herd.