4. Bovine Tuberculosis in Man.—In the past widely diver gent views have been entertained, from the belief that the bovine strain never affected man to the opposite view, that all human infection was derived from bovine sources. Such widely divergent views naturally stimulated research and as a consequence it is now possible to say with some degree of finality that the bovine tubercle bacillus is responsible for from to to 15 per cent. of all human tuberculosis, the clinical types produced being chiefly cervical adenitis, abdominal tuberculosis and generalized tuberculosis of alimentary origin. It is exceed ingly rare in pulmonary tuberculosis, which is practically due only to the human strain of the tubercle bacillus. Infection is usually found in children under sixteen years of age, while susceptibility is greatest during the first five years of life.
In New York City 7 per cent. of the deaths among those of less than five years of age are due to bovine tuberculosis. Infection is contracted through the consumption of contami nated milk. When we consider the wide prevalence of the disease in cattle, as indicated by the following table and the small proportion of human infection, one must conclude that human infection is not very easy.
The bovine tubercle bacillus has been found in the following proportions in the milk supply of different cities: New York City. r6 per cent. of milk specimens examined.
Washington City 2.7-6.7 per cent. of milk specimens examined.
Chicago 7.9 per cent. of milk specimens examined.
Manchester, England 8.9 per cent. of milk specimens examined.
Tuberculosis is widespread among the dairy herds of the United States, though by constant effort, reduction is being gradually accomplished. A few years ago it was found that 302 of 421 dairy herds examined in the state of New York were infected. It has been authoritatively estimated that 3o per cent. of all dairy herds in the U. S. are infected.
The presence of tubercle bacilli in milk usually arises as a result of milk contamination with bovine feces. Mammary tuberculosis is very rare in cattle, only from z to io ten cent. of infected cattle having a tuberculous mastitis. On the other hand, pulmonary involvement is most common. The sputum instead of being expectorated is swallowed and the organisms pass out of the body with the feces.
Since the disease is chronic and the infection commonly widespread in invaded herds, it is easy to understand that the contamination of the milk from an infected dairy will probably be continuous. On the other hand, the tubercle bacillus is very slow growing, so that in the interval between production and consumption of the milk no appreciable increase in the number of organisms will take place.
Pasteurization of milk at a temperature of at least is the only safeguard against milk-borne tuberculosis. Further more pasteurization should be in closed vessels to avoid the formation of the scum upon the surface of the milk which serves to insulate some of the organisms from the heat.
The tuberculin testing of dairy cattle and the slaughtering of those found to react is a very satisfactory means of eradicat ing the disease and has been successfully practiced for some time. This method, however, gives rise to serious losses in the case of blooded stock. To overcome this disadvantage the Bang system was originated. Reacting cows without open.
lesions are not killed, but are permitted to be bred. Following calving the calves are immediately separated from their mothers and never permitted to suckle. The cows are milked and the milk pasteurized before being fed to the calves. Of course the reacting cows used for breeding are separated from all other healthy cattle. The success of this method lies in the fact that intrauterine infection is so rare as to be a negligible factor in the dissemination of the disease. As a consequence, the desir able qualities of highly bred cattle may be perpetuated and the losses are very much diminished, while healthy uninfected progeny are secured, and in the course of a few years a farm is clear of tuberculosis.
5. Typhoid typhoid fever was first recognized in 1857, over three hundred similar outbreaks have been reported in the literature and this must represent a minor fraction of the total.
Milk-borne typhoid is urban rather than rural in character and is probably responsible for a considerable proportion of endemic typhoid, represented chiefly as small epidemics. Ogan estimates that 39 per cent. of all typhoid fever in New York City is milk-borne. In Washington City the minimum number of milk cases represent from 9 per cent. to r r per cent. of all typhoid, these cases occurring chiefly in small epidemics. An interesting bit of data in this connection is the following observation from Washington.
These figures clearly indicate that milk is a considerable factor in endemic typhoid, and demonstrates the protective value of pasteurization.
In considering the introduction of the typhoid bacilli into the milk let us separately consider the dairy and the retail end.
Infection of the milk at the dairy or producing farm has been observed to have resulted from the following practices or cir cumstances in different epidemics (Fig. 64): (a) Unrecognized cases serving as milkers or handlers.
(b) The nurse of a typhoid patient serving as a milker or milk handler (Fig. 63).
(c) Washing milk utensils in contaminated water.
(d) Washing milk utensils with the same dish cloths used for dishes of a typhoid case.
(e) Adulteration of milk with infected water.
From the standpoint of the distribution of a milk supply, the following circumstances have given rise to epidemics: (a) Unrecognized cases or carriers delivering milk or working in milk depots.
(b) Use of bottles from premises on which typhoid cases existed without their previous sterilization.
The development of the typhoid bacillus in milk is rapid as the temperature rises above ten degrees C. As a consequence most milk outbreaks occur during the summer months or during warm periods in winter. The outbreaks are explosive in char acter and affect milk drinkers most heavily, particularly women and children. The introduction of the infective agent is inter mittent and as a result several explosive crops of cases may be observed.
6. Other Milk-Borne Infections.—The distribution of scarlet fever, diphtheria or septic sore throat by milk does not essen tially differ from that of typhoid fever, although they are of rarer occurrence.
7. Other Milk Products as Routes of Infection.—Dairy products, as well as fresh milk may serve to distribute infective agents. Thus the cream supply, ice cream, butter and butter milk must be borne in mind in the investigation of epidemics.