TYPHOID FEVER 12/ 



' typhoid-fly ' is open to some objection as conveying the 

 erroneous idea that the fly is solely responsible for the spread 

 of typhoid." For many reasons exact bacteriological proof 

 of the conveyance of this infection by flies is difficult in the 

 majority of outbreaks and consequently we have to rely on 

 indirect evidence as is done in water analyses. If on bacterio- 

 logical examination a sample of water is found to contain fsecal 

 bacteria, and it can be shown that the source of supply is liable 

 to contamination with human sewage, the water is considered 

 to be dangerous, not because the ordinary faecal bacteria are 

 themselves the cause of specific disease, but because the organisms 

 causing typhoid fever and other intestinal diseases may find their 

 way into the water in the same way as the faecal bacteria. 

 Typhoid bacilli have only rarely been isolated from infected 

 waters, though numerous undoubted water-borne epidemics have 

 been recorded. Flies we know constantly carry and distribute 

 faecal bacteria and no doubt carry the bacteria of intestinal 

 diseases, when suitable opportunities occur. 



The difficulties in the way of producing definite bacteriological 

 proof of infection through flies are due to several different causes. 

 The typhoid bacillus does not originate in the fly ; the latter 

 must obtain infection from some pre-existing case of the disease 

 in the human subject either by contact with some article soiled 

 by the patient or more usually by visiting infected excreta. 



Modern research has shown that many patients continue to 

 excrete B. typhosus in the urine or faeces long after the symptoms 

 of the disease have disappeared. Such persons, who often have 

 the disease in a mild and almost unrecognizable form, and subse- 

 quently remain in perfect health, are termed ' carriers.' Some 

 of these carriers constantly excrete the bacilli, while others only 

 do so at intervals, but the majority continue to excrete them for 

 prolonged periods, often many years. Numerous outbreaks have 

 been traced to unrecognized carriers, and it is now universally 

 recognized that many of them, especially those who have to do 

 with the preparation of food, constitute a serious danger to the 

 health of the community in which they live. 



Flies cannot obtain B. typhosus from the excreta of normal 

 individuals, but can do so from the faeces of apparently healthy 



