Tropical Medicine and Hygiene 



PART II. DISEASES DUE TO METAZOA. 



CHAPTER I. 

 INTRODUCTORY. 



THE Metazoa include many forms of animal life para- 

 sitic in man. Some of these parasites cause definite 

 diseases which may lead to death or disablement. They 

 serve as good examples of the various kinds of parasitism. 

 Thus the filariae are examples of metazoa parasitic, in 

 vertebrates or invertebrates, during their entire existence. 

 Such parasites for their continued reproduction and 

 multiplication require the presence not only of human 

 beings but also of a suitable intermediate carrier. These 

 carriers may be insects such as mosquitoes, or biting flies, 

 or crustaceans such as cyclops. Molluscs also are carriers, 

 as some of the trematodes develop in them. Meteoro- 

 logical conditions must be such that both growth of the 

 parasite in these cold-blooded hosts will take place, and 

 also that conditions favourable for the life and growth 

 of these invertebrate hosts exist, otherwise the continued 

 propagation of the parasite could not take place. When 

 the parasites have been introduced into the warm-blooded 

 host they may continue their existence indefinitely. 



Other parasites of man, as some of the tapeworms, are 

 parasitic during different phases of their existence in 

 mammals of different species, and in the case of such para- 

 sites meteorological conditions are of little importance. 

 Proximity of man to the other mammals is the main 

 condition required in some cases, in others it is a question 

 of one animal consuming the flesh of the others. 

 i 



