SOME EPIDEMIOLOGICAL AND BIOLOGICAL PROBLEMS 

 IN WATER-BORNE AMOEBIASIS 



B7 SHIH L. CHANG 



DEPARTMENT OF SANITARY ENGINEERING, GRADUATE SCHOOL OF ENGINEERING AND 

 SCHOOL OF PUBLIC HEALTH, HARVARD UNIVERSITY, CAMBRIDGE, MASS. 



Interest in the problem of amoebiasis in this country reached a 

 climax in the few years following the Chicago epidemic of amoebic 

 dysentery in 1933 (Natl. Inst. Health Bui.). Toward the end of the thirties, 

 the problem was more or less tossed out of the window and attracted atten- 

 tion only from those interested in tropical diseases. Although it has been 

 estimated that from 5 to 10% of the general population pass the cysts of 

 Entamoeba histolytica (Craig and Faust 1943), the infection has not been 

 considered a serious public health hazard. This is partly due to the fact 

 that in most cases, the infection is in a quiescent state, relatively few cases 

 developing clinical amoebiasis which requires medical care, and partly due 

 to the fact that the highest incidence of even quiescent infections has been 

 found in those localities where health problems have not yet received full 

 attention of health authorities. 



While it cannot be denied that in spite of the world-wide occurrence 

 of quiescent amoebiasis, amoebic dysentery and liver abscess are usually 

 diseases of the tropics and subtropics, the Chicago epidemic has clearly 

 shown that under certain circumstances, severe clinical amoebiasis may 

 occur in epidemic form even in the temperate zone. It may also be pointed 

 out that while the carrier rates were high in the Southern States, e.g., 17.3, 

 11.4 and 36.4% in Tennessee and 25.9 and 14.9% in New Mexico, they were 

 also impressive in some of the surveys made in the Northern States, e.g., 

 4.6, 7.7, and 10.7% in Minnesota and 4.1 and 11.1% in Pennsylvania (Craig 

 and Faust 1943). These carriers not only constitute a potential source of 

 infection to others, but may themselves develop amoebic dysentery when 

 they enter the tropics or subtropics, or when certain changes take place in 

 the alimentary canal. 



The successful control of an infectious disease demands a thorough 

 understanding of its mode of transmission. Unfortunately, it is an extremely 

 difficult task to ascertain the mode of transmission of some infectious 

 diseases. For instance, in spite of extensive epidemiological and experi- 

 mental studies on human poliomyelitis in the last 15 years, we are still 

 in the dark as to how this infection spreads in a community. Controversial 

 opinions also exist on the mode of transmission of amoebiasis. In places 

 such as mental institutions and orphanages where water supply is well 

 controlled and where personal hygiene of an overcrowded population is 

 usually bad, direct contact and contamination of food and drink by car- 

 riers are probably the only two routes by which amoebiasis spreads. How- 



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