338 Microbes and You 



pig or rabbit virulence tests. Bacteriophage has been found to 

 alter non-virulent strains of otherwise typical diphtheria organisms 

 in such a way as to make them suddenly virulent. 



MYCOBACTERIUM TUBERCULOSIS 



Non-motile rods, ranging in size from 0.3 to 0.6 by 0.5 to 4.0 

 microns, straight or slightly curved, occurring singly and occa- 

 sionally in threads. Sometimes branched. Stain uniformly or 

 irregularly, with banded or beaded forms. Acid-fast. Gram 

 positive. Growth in all media is slow, requiring several weeks 

 for development. Optimum temperature 37° C. Facultative. 

 Produce tuberculosis in man, monkey, dog, and parrot. Can 

 infect guinea pigs, but not rabbits. 



Most tuberculosis in human beings is pulmonary, and infection 

 is acquired principally through droplet infection or by direct 

 contact with infected individuals. Inhalation of dust containing 

 dried sputum should not be overlooked as a potential source of 

 infection. Bovine tuberculosis may be contracted by drinking raw 

 milk from infected cows. The death rate from tuberculosis in the 

 United States has had a dramatic drop in the last fiftv vears from 

 well over two hundred deaths per one hundred thousand population 

 to less than thirty deaths per hundred thousand at the present 

 time. This progress can be attributed to decreased consumption 

 of raw milk, better diagnostic technics, improved treatment of 

 recognized cases, and increased facilities for keeping infected 

 persons isolated from healthy individuals. The disease is still 

 one of tremendous public health significance, however, as evidenced 

 by the thirty-three thousand deaths annually in the United States. 

 Nearly one-half million persons are suffering from tuberculosis in 

 our country, and this is a challenge to public health authorities 

 who know that tuberculosis is a preventable disease. 



Pulmonary tuberculosis is almost always due to the human 

 tubercle organisms contracted from infected persons or their dis- 

 charges, while non-pulmonary tuberculosis (bones, joints, viscera) 

 appears to be food-borne. 



Detection of infected individuals is difficult in the earlv stages 

 of the disease, since clinical symptoms mav be absent for months. 



