CHAPTER X 



OTHER SPOROZOA, AND OBSCURE OR INVISIBLE 

 PARASITES 



ALTHOUGH the class Sporozoa includes a very large number of 

 species, all of which are parasitic, and many of them the cause of 

 fatal diseases in vertebrate as well as invertebrate animals, yet 

 very few other than the malaria parasites, already discussed, 

 are normally parasitic in man, and none of these can be looked 

 upon as of prime importance in the causation of human disease. 

 Of greatest importance, perhaps, are the Coccidiida or coccidians, 

 which in lower animals are frequently the cause of fatal diseases 

 and have been known to be fatal to man, though in some cases 

 causing very little inconvenience. Another sporozoan parasite 

 which is of importance where it occurs is Rhinosporidium, which 

 produces tumors in the nose. A group of muscle-dwelling 

 Sporozoa, the Sarcosporidia, occur accidentally or sporadically 

 in man. 



There is another group of Sporozoa, the Piroplasmata, related 

 to the malaria parasites, which are the cause of some of the most 

 fatal diseases of domestic animals, including Texas fever and East 

 Coast fever of cattle, biliary fever of horses, etc. These diseases 

 are invariably, as far as known, transmitted by ticks. There is 

 one human parasite, Bartonella bacilliformis, the cause of Oroya 

 fever of Peru, which is thought to belong to this group of organ- 

 isms. There is a possibility that Rocky Mountain spotted fever 

 and the related Japanese disease, kedani, may also be caused by 

 Piroplasmata, though the parasites have not yet been discovered. 



There are a number of other diseases, some of them of great 

 importance, of which the " germ " either has never been seen or is 

 of obscure nature. It is not always possible to guess -at the 

 nature of such undiscovered parasites but in some cases we can 

 get a fairly accurate conception of them from a study of the course 

 of the diseases they cause, the conditions under which they thrive 

 and their means of dissemination. One by one the villains be- 



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