2 DISEASES DUE TO PROTOZOA 



DISEASES DUE TO PROTOZOA. 



INTRODUCTION TO PROTOZOOLOGY. 



The Protozoa are now definitely proved to be factors of the 

 greatest importance in the causation of Tropical Diseases. It is 

 essential that all tropical practitioners should be acquainted with the 

 outlines at least of their life-history and comparative pathology. One 

 only has to mention such diseases as malaria, kala-azar, trypano- 

 somiasis, framboesia tropica, and relapsing fever to indicate the large 

 amount of tropical pathology coming under this head. 



DEFINITION. 



Protozoa are unicellular organisms, occurring singly or in clusters, 

 either non-parasitic, parasitic on the lower animals only, parasitic during 

 part of their existence, or parasitic in different animals during different 

 stages of their development, and reproducing themselves — 



Asexually by binary fission (schizogony) ; 



Sexually by budding (sporogony); 



Sexually by rejuvenescence by conjugation. 



ORIGIN OF INFECTION. 



Very probably the primitive form of protozoon had some of the 

 characteristics of the simple amoeba. This could be taken into the 

 alimentary tract, from thence into the blood-stream, consequently 

 facilitating blood-sucking insecta in carrying out their part in the 

 transmission of the protozoa in question. 



The blood of man may have been infected from human intestinal 

 excreta or from infective material coming from the intestinal tract of 

 some invertebrate. 



The first form was undoubtedly non-pathogenic, pathogenicity 

 probably beginning in bats and birds, followed some time later by 

 pathogenicity in man, the intermediate links being lost. 



Some protozoa cannot pass through the placenta, e.g., the malarial 

 parasite, while others can pass through and infect the foetus, e.g., the 

 spirochcetes and treponemata. 



Many of the insect "carriers" infect their eggs, and thus hand 

 down the infection to a new generation of blood-suckers. 



The hasmatozoan types may live — 



In the blood-stream free, e.g., trypanosomes ; 



In the red blood cells, e.g., malarial parasite; 



In the white blood cells, e.g., Leishman-Donovan body ; 



In the endothelial cells, e.g., Leishman-Donovan body. 



