EPIDEMIOLOGICAL AND BIOLOGICAL PROBLEMS 29 



problems to be encountered in the control of water-borne amoebiasis. From 

 these characteristics, it is apparent that if polluted water is to be used as 

 a source of public water supply, it must be considered as a potential 

 source of amoebic infection and must be treated as adequately as is the 

 practice in a modern municipal water works, namely, by storage, floccula- 

 tion and sedimentation, filtration, and chlorination. The cysts that may 

 be present in the water are completely removed by the combined effect 

 of the first three methods but will not be killed by chlorination as normally 

 practiced in water works. If chlorination is the only method available for 

 destruction of cysts in water, then superchlorination or breakpoint chlorina- 

 tion must be employed. For emergency treatment of water to destroy 

 cysts, superchlorination at pH 5.0 to 6.0 followed by dechlorination or treat- 

 ment with elemental iodine to give a residual of about 4 to 5 ppm in 10 

 minutes at pH 5.0-7.0 would be satisfactory. The use of 30 to 50 ppm 

 of some of the best cationic detergents is also feasible, but this treatment 

 would produce a bitter and slightly soapy water. Ozone is a powerful cysti- 

 cidal agent, but its use is bound to be handicapped by its low solubility and 

 the difficulty of distributing it evenly in a large body of water. 



It goes without saying that one of the best control measures of amoebia- 

 sis is a thorough treatment of the cases of amoebic dysentery to prevent 

 them from swelling the army of carriers and a thorough treatment of all 

 carriers. While the former can be effectively carried out, the treatment 

 of all carriers, particularly in areas where the carrier rate is high, would 

 certainly encounter many difficulties. 



V. Summary 



In this paper, some of the clinical features of amoebic infection have 

 been discussed to bring out the difficulties involved in the study of the 

 epidemiology of this infection for establishing the mode of transmission. 

 These features are quiescent infection, primary and secondary amoebic 

 dysentery, incubation period, and the not-too-well-understood factors 

 involved in the provoking of amoebic dysentery. 



The water-borne nature of amoebiasis has been discussed. Evidences 

 such as the Chicago epidemic, the Chicago Stockyard fire outbreak of 

 enteric infections, and finding of E. histolytica-\ike cysts in sewage and 

 sewage effluent are brought out and analysed to show the probable role 

 played by polluted water in the spread of amoebiasis. 



The biological characteristics of the cysts of E. histolytica have been 

 presented, such as the cultivation of amoebae, the specific gravity and 

 settling of amoebic cysts in water and sewage, the removal of amoebic 

 cysts from water by flocculation and sedimentation and by filtration 

 through sand or diatomaceous earth filters, and the resistance of amoebic 

 cysts to various water disinfectants, particularly the halogens and halogen 

 compounds. 



At the end of the paper, the thought is expressed that if amoebiasis is 

 not a serious public health hazard in the United States as a whole, it is 



