XIV 



Immunity and Resistance 



Natural resistance 



Acquired resistance 

 Active immunization 



Leishmania 



Trypanosoma 



Babesia 



Plasmodium 



Coccidia 

 Passive immunization 



Trypanosoma 



Plasmodium 



Factors involved in acquired resistance 



Antibodies 



Defensive mechanisms in trypanosome 



infections 

 Defensive mechanisms in malaria 



Serological diagnosis of infection 

 Agglutinin tests 

 Precipitin tests 

 Complement-fixation tests 

 Skin tests 

 Adhesion tests 



Serological differentiation of species 



Literature cited 



NATURAL RESISTANCE 



J. 



usT AS THERE ARE natural infections with Protozoa, so there 

 appear to be natural immunities to protozoan parasites, immunities 

 which probably should be attributed to biological incompatibility. A 

 natural immunity may be absolute, or it may be a relative immunity 

 which can be overcome by massive inoculation or by debilitating factors. 



The degree of natural resistance to a given parasite commonly varies 

 with the host and may vary widely even within a single genus, as dem- 

 onstrated in Peromyscus (128). In highly susceptible species of Peromyscus, 

 infection with Trypanosoma hrucei is usually fatal within a week. In 

 another group of species, the infection is subacute and survival of the 

 mice averages about three months. In a third group, the infection runs 

 a chronic course and most of the mice apparently recover. 



Within a single species, racial differences in natural resistance may 

 exist, although little is known about this aspect of immunity against 

 Protozoa. Differences between the apparent resistance of Europeans and 

 that of natives to tropical diseases have often been emphasized as ex- 

 amples of racial differences in immunity. These differences also have 



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