THE FLIES THAT CAUSE MYIASIS IN MAX 15 



withstands a critical examination, we must admit the possibility of 

 accidental parasites, in some cases and under certain conditions. 

 maintaining themselves in the human digestive tract. 



Komarek ( 76) and Causey ( 20) have attempted to disprove the pos- 

 sibility of infestation of the human digestive tract by fly larvae. The 

 arguments of these authors are based on the premises. first, that the 

 active normally free-living larvae (in contrast to Gasterophit/us) can- 

 not survive the relatively anaerobic conditions existing in the human 

 digestive tract, and second, that the mechanical movements of the tract 

 and the action of the digestive juices would destroy the larvae even if 

 they could obtain sufficient oxygen. Komarek subjected larvae of 

 various species of flies reported to be involved in intestinal myiasis to 

 conditions that would simulate anaerobic conditions of the stomach and 

 intestine: he also fed some living larvae to a cat. All the larvae per- 

 ished. Causey used cats and dogs as experimental animals : in all eases 

 the larvae "were found to be killed or immobilized in the stomach within 

 3 hours and. on passage into the intestinal tract, were eventually 

 digested. In no instance could living larvae of any of these species 

 be discovered in the large intestine or passed feces of the experimental 

 animals. 5 ' 



The conclusions of Komarek and Causey are criticized by Riley 

 ( 120 ) . As that author points out — 



a limited series of experiments may be wholly negative without justifying the 

 disregard of many detailed reports by careful physicians and entomologists who 

 have been well aware of chances of error involved. Similar negative results 

 could be obtained by administering infective stages of cat ascarids to human 

 beings. Children everywhere are exposed to innumerable opportunities to pick 

 up infections of these worms and yet instances of their development in man are 

 So rare as to lie veritable medical curiosities. In those rare instances scim- 

 abnormal condition of the individual has made it possible for the worms to 

 maintain themselves. The possibility of this occurring in the case of fly larvae 

 would seem fully established * * *. 



Case records of enteric myiasis in man often indicate gastric and 

 intestinal disturbances which have endured over a considerable period 

 of time, sometimes years. This has sometimes been interpreted as 

 suggesting, or indicating, that the larvae were reproducing paedoge- 

 netically within the digestive tract. Following Riley's suggestion, one 

 might conclude that in such cases digestive disturbances of another 

 nature may modify conditions within the digestive tract to such a 

 degree that larvae not normally capable of living there could endure 

 the new conditions. Ingested air might supply the oxygen for at least 

 part of the journey through the alimentary canal: flatulence is usually 

 associated with this form of myiasis. If oxygen is not available at 

 all times, it must be considered that even active maggots are capable 

 of undergoing periods of suspended activity. Extended periods of 

 infestation, however, may be explained in some instances by reinfesta- 

 tion. Sometimes the habits of the patient are such that this is a strong 

 possibility. That the presence of fly larvae in the digestive tract could 

 produce symptoms such as are usually ascribed to enteric m\ iasis. not- 

 withstanding Causey's opinion to the contrary, should seem reasonable 

 when one considers the effect the rasping action of savage mouth hooks 

 might have on the intestinal wall and the possibility of toxic and 

 infective effects following. 



