22 LIMNOLOGY, WATEK SUPPLY AND WASTE DISPOSAL 



II. The Role of Polluted Water as a Transmitting Agent of Amoebiasis 



As early as 1926, Craig mentioned the possibility of water-borne 

 amoebiasis. Clark (1925) reported the marked reduction in post-mortem 

 incidence of amoebic infection in Panama following the introduction of a 

 modern water supply; but the evidence has been considered as too non- 

 specific to support the view that amoebiasis is water-borne, since many 

 other factors, such as improvement of personal hygiene and change of eat- 

 ing habits, could have altered at the same time and might also have 

 affected the incidence of amoebic infection. Nevertheless, there have been 

 accumulated a few substantial facts that provide sufficient ground to believe 

 that polluted water may be one of the most important sources of amoebiasis. 



A. The Chicago Epidemic. In spite of the skepticism expressed by 

 some epidemiologists and eminent tropical disease experts, the Chicago 

 epidemic of amoebic dysentery, in several of its essential features, still 

 stands out as an example of water-borne amoebiasis. As stated before, 

 Wenyon (1947) expressed skepticism on the basis that the incubation 

 period was too short for amoebic dysentery; but the number of cases hav- 

 ing an incubation period of less than one week was so small that they 

 should carry no weight in judging the nature of the epidemic. 



Although the finding of E. histolytica-like cysts in the cross-connection 

 pipe removed at the time of inspection (Natl. Inst. Health Bui.) served 

 only as weak evidence for the water-borne nature of the epidemic, there 

 were a few essential observations that strongly supported the water-borne 

 theory. First, if the epidemic were bacillary dysentery, there should 

 have been a very large number of cases of bacillary dysentery noticed 

 during the early part of the epidemic. On the contrary, the epidemic 

 was reported to be uncomplicated by the existence of outbreaks of bacterial 

 enteric infections (Natl. Inst. Health Bui.). Second, the fact that amoebia- 

 sis, including the asymptomatic infection, has been successfully controlled 

 in the two Chicago hotels after the sanitary defects were corrected is also 

 strong evidence that the source of infection of that epidemic was of water 

 origin. Third, the recent outbreak of bacillary dysentery in Kansas (Kin- 

 naman and Beelman 1944) in which 3000 cases were reported was not 

 complicated by cases of amoebic dysentery. 



B. The Chicago Stockyard Fire Outbreak. In the Chicago Stockyard 

 fire in 1934 (Hardy and Spector 1935), at least 11 cases of amoebic 

 dysentery were noticed along with over 300 cases of dysentery and 78 

 cases of typhoid fever among the firemen and some spectators who drank 

 water from a pipe which was used to supply water to the stock and fed 

 with sewage-polluted water and sewage effluent. It is of particular interest 

 to note that among the 216 firemen who developed enteric infection of 

 various degrees of severity, 57% showed cysts of E. histolytica in their 

 stools, while only 15% of 161 firemen who did not drink the polluted water 

 and consequently were not infected, had the cysts. While it could be argued 

 that the 11 cases of amoebic dysentery might have been secondary cases 

 developed in carriers, the much higher percentage of cyst passers among 



