14 MISC. PUBLICATION 631, U. S. DEPT. OF AGRICULTURE 



other hand, occur in the subcutaneous connective tissue, though from 

 time to time they emerge toward the surface ; the tunnels are broader 

 and not so well-defined. The activity of the larva may cause severe 

 pain. Each type is discussed in more detail under the heading of its 

 genus. In both types man is an accidental host. 



ENTERIC MYIASIS 



Under this heading will be considered myiasis of the stomach, of 

 the intestine, or of both, it being impracticable for the most part to 

 try to separate them. This type of myiasis is most representative of 

 Patton's third group or accidental myiasis-producing flies. 



Great care is necessary in diagnosing enteric myiasis. Undoubtedly 

 many cases reported to be such, some of which become recorded in the 

 literature, are attributed to contamination of stools or to cases not 

 adapted to this interpretation of the facts. The horror of intestinal 

 worms, in which category the layman usually includes maggots or 

 almost anything wormlike, is so firmly implanted in the popular mind 

 that the presence of maggots, actually or supposedly, in fresh stools is 

 usually a source of alarm. One is likely to overlook the possibility 

 that there was previous contamination of the chamber vessel, or that 

 the maggots might have entered the rectum, vulva, or urinary passages 

 or bladder, and in this way might have been passed with the feces or 

 urine. 



Contamination of the stools can easily be accomplished, especially 

 by species of Sarcophaga, in which the maggots are produced alive, 

 and in which the duration of the first two larval instars is often very 

 brief. It may therefore be possible to find third instars resulting from 

 subsequent contamination in stools no more than a day old. Further- 

 more, the mother fly will often drop her maggots through gauze or 

 deposit them in places where they may crawl through cracks through 

 which it would seem impossible for them to pass. A covered chamber 

 vessel, therefore, is not necessarily maggot -proof, at least so far as 

 Sarcophaga is concerned. 



In relation to the work of both Komarek and Causey, the selection 

 of experimental animals, both mammalian and arthropod, may be 

 criticized. Dogs and cats are carnivores, and conditions within their 

 digestive tracts are certainly not identical with those of the human. 

 In regard to the Diptera used,- Causey selected Drosophila melano- 

 gaster, Phaenicia sericata, Phormia regina, Callitroga macellaria, 

 Sarcophaga securifera, and Calliphora erythrocephala; Komarek, 

 Calliphora vomitoria, Sarcophaga carnaria, Musca domestica, and 

 Piophila casei. It should be noted that Sarcophaga haemorrhoidalis, 

 Tubifera tenax, and species of Fannia, Muscina, and Megaselia, the 

 etiological agents involved in most of the best authenticated cases of 

 enteric myiasis, are absent from both lists, whereas Piophila casei, 

 which also belongs in that category, is mentioned by Komarek only in 

 general and not in relation to any particular experiments. 



However, one should not take the extreme view that enteric parasit- 

 ism by fly larvae is impossible. The fact that Gasterophilus larvae 

 develop normally as gastrointestinal parasites of the horse and related 

 animals should disprove this theory. If the evidence is sufficient and 



