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 or 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 arc 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 (iqio) 
