CHAPTER VIII 



ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC 

 PROTOZOA 



MOSQUITOES AND MALARIA 



Under the name of malaria is included a group of morbid symp- 

 toms formerly supposed to be due to a miasm'or bad air, but now 

 known to be caused by protozoan parasites of the genus Plasmodium, 

 which attack the red blood corpuscles. It occurs in paroxysms, 

 each marked by a chill, followed by high fever and sweating. The 

 fever is either intermittent or remittent. 



There are three principal types of the disease, due to different 

 species of the parasite. They are: 



1 . The benign-tertian, caused by Plasmodium vivax, which under- 

 goes its schizogony of asexual cycle in the blood in forty-eight hours 

 or even less. This type of the disease, characterized by fever 

 every two days, is the most wide-spread and common. 



2. The quartan fever is due to the presence of Plasmodium 

 malaria, which has an asexual cycle of seventy-two hours, and there- 

 fore the fever recurs every three days. This type is more prevalent 

 in temperate and sub-tropical regions, but appears to be rare every- 

 where. 



3. The sub-tertian "aestivo-autumnal," or "pernicious" fever 

 is caused by Plasmodium falciparum. Schizogony usually occurs 

 in the internal organs, particularly in the spleen, instead of in the 

 peripheral circulation, as is the case of the tertian and quartan forms. 

 The fever produced is of an irregular type and the period of schizogony 

 has not been definitely determined. It is claimed by some that the 

 variations are due to different species of malignant parasites. 



It is one of the most wide-spread of human diseases, occurring 

 in almost all parts of the world, except in the polar regions and in 

 waterless deserts. It is most prevalent in marshy regions. 



So commonplace is malaria that it causes little of the dread 

 inspired by most of the epidemic diseases, and yet, as Ross says, 

 it is perhaps the most important of human diseases. Figures regard- 

 ing its ravages are astounding. Celli estimated that in Italy it 

 caused an average annual mortality of fifteen thousand, representing 

 about two million cases. In India alone, according to Ross (1910) 



1 86 



