154 Arthropods as Simple Carriers of Disease 



may pass through their bodies and be scattered in a viable condition 

 in the feces of the fly for at least two days after feeding. Similar, 

 results have been reached in experiments with cholera, tuberculosis 

 and yaws, the last-mentioned being a spirochaete disease. Darling 

 (19 13) has shown that murrina, a trypanosome disease of horses 

 and mtiles in the Canal zone is transmitted by house-flies which feed 

 upon excoriated patches of diseased animals and then pass to cuts 

 and galls of healthy animals. 



Since it is clear that flies are abimdantly able to disseminate 

 viable pathogenic bacteria, it is important to consider whether they 

 have access to such organisms in nature. A consideration of the 

 method of spread of typhoid will serve to illustrate the way in which 

 flies may play an important r61e. 



Typhoid fever is a specific disease caused by Bacillus typhosus, 

 and by it alone. The causative organism is to be found in the excre- 

 ment and urine of patients suffering from the disease. More than 

 that, it is often present in the dejecta for days, weeks, or even months 

 and years, after the individual has recovered from the disease. 

 Individuals so infested are known as "tj^hoid carriers" and they, 

 together with those suffering from mild cases, or "walking typhoid," 

 are a constant menace to the health of the community in which they 

 are fotmd. 



Human excrement is greedily visited by flies, both for feeding and 

 for ovipositing. The discharges of typhoid patients, or of chronic 

 "carriers," when passed in the open, in box privies, or camp latrines, 

 or the like, serve to contaminate myriads of the insects which may 

 then spread the germ to human food and drink. Other intestinal 

 diseases may be similarly spread. There is abundant epidaemiologi- 

 cal evidence that infantile diarrhoea, dysentery, and cholera may be 

 so spread. 



Stiles and Keister (19 13) have shown that spores of Lamblia 

 intestinalis, a flagellate protozoan living in the human intestine, 

 may be carried by house-flies. Though this species is not normally 

 pathogenic, one or more species of Entamoeba are the cause of a type 

 of a highly fatal tropical dysentery. Concerning it, and another 

 protozoan parasite of man, they say, "If flies can carry Lamblia 

 spores measuring 10 to 7[j„ and bacteria that are much smaller, and 

 particles of lime that are much larger, there is no ground to assume 

 that flies may not carry Entamceba and Trichomonas spores. 



