13 



Disease-Producing Microorganisms 

 in the Soil and Their Control 



Survival of Human and Animal Pathogens in the Soil 



Microbes capable of causing various human and animal diseases 

 find their w^ay into the soil and into water basins in very large num- 

 bers, either in the excreta of the infected host or in the dead and 

 infected residues of the latter. If one considers the millions of years 

 that animals and plants have existed on this planet, one can only 

 surmise the great numbers of microbes causing the numerous dis- 

 eases of all forms of life that must have thus been introduced into 

 soils and surface waters. What has become of all the bacteria caus- 

 ing typhoid fever, dysentery, cholera, diphtheria, pneumonia, bu- 

 bonic plague, tuberculosis, and leprosy in man, mastitis and abortion 

 in cattle, and numerous diseases of other animals? This question 

 was first raised by medical bacteriologists in the eighties of the last 

 century. The soil was searched for the presence of bacterial agents 

 causing infectious diseases and responsible for epidemics. The re- 

 sults obtained established beyond doubt that, with very few excep- 

 tions, organisms pathogenic to man and to animals do not remain 

 alive in the soil for very long. 



A few disease-producing microorganisms, however, are able to 

 survive in the soil for considerable periods. One need only mention 

 the organisms causing tetanus, gas gangrene, skin infections, actino- 

 mycosis and blackleg in cattle, coccidiosis of poultry, hookworm in- 

 fections, trichinosis, enteric disorders in man. To these must be 

 added diseases caused by various other bacteria, actinomycetes, and 

 fungi. This is also true of numerous plant diseases, such as potato 

 scab, root rots, take-all of cereal crops, and the damping-off diseases 

 of vegetables. The great majority of disease-producing microorgan- 

 isms, notably the human and animal pathogens listed above, are able 

 to remain in an active and reproducible state in the soil for only 



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