562 Protozoa of the Digestive and Urogenital Tracts 



E. histolytica, and there seems to be fairly good correlation between the 

 canine and the human response to known amoebacidal drugs (160). 

 Young rats also have been used to advantage (85). 



Problems in control of amoebiasis 



The transfer of E. histolytica is a simple inatter. All that is neces- 

 sary is for viable stages, voided in the feces of an infected individual, to 

 reach the mouth of another host and be swallowed. The control of in- 

 testinal amoebiasis involves nothing more than preventing the comple- 

 tion of this sequence. The fact that no immediate solution of the problem 

 is in sight depends not only upon the biological characteristics of E. 

 histolytica but also upon human behavior. That the combination is still 

 beyond control by current public health practice is attested by the wide- 

 spread distribution of E. histolytica. 



The encysted stage of E. histolytica is well adapted to its normal 

 method of transfer. At temperatures below 22° cysts may remain viable 

 for 1-6 weeks under favorable conditions, with time of survival showing 

 an inverse relationship to temperature (29a). Cysts also are viable for at 

 least several hours after ingestion by flies and passage through the insects 

 (131, 179). Pollution of the soil with cysts is an important source of in- 

 fection whenever human excrement is used as fertilizer. Under suitable 

 experimental conditions, cysts remain alive in soil for at least eight days 

 at 28-34° (14). Consequently, uncooked vegetables from contaminated 

 soil are potentially dangerous. Treatment of such vegetables Avith dilute 

 acetic acid may be an efl:ective prophylactic measure (15). 



The infected individual may distribute cysts widely, as in the "general 

 pollution of the environment" noted in a revealing survey of a children's 

 home (79). Cysts were recovered from the hands of children, from soiled 

 clothing, from the bottom of a laundry chute, from damp sand in a play- 

 box, from a wading pool, and from the floor of the pool after drainage. 

 In general, any conditions under which sanitary precautions are relaxed 

 or neglected will contribute to infection. Crowding in asylums, prisons, 

 and other institutions may be a contributory factor, especially when 

 coupled with carelessness or ignorance. A recent outbreak in an eastern 

 state hospital is illustrative. Investigation showed that a toilet used by 

 kitchen attendants was without soap and paper, that attendants caring 

 for amoebic patients spent part of their time working in the kitchen, and 

 that carriers of E. histolytica had been serving as cooks and kitchen 

 helpers. 



Since cysts may remain viable for 15-45 minutes under the fingernails 

 (4), the infected food-handler has often been considered a major source 

 of infection (40, 41), both within the family and in hotels and restaurants. 

 Although there are no adequate data and at least one statistical study has 

 failed to support such transmission (147), the burden of proof would seem 



