CHAPTER VIII
ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA
Mosquitoes and Malaria
Under the name of malaria is included a group of morbid symptoms 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 undergoes 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 malariæ, which has an asexual cycle of seventy-two hours, and therefore the fever recurs every three days. This type is more prevalent in temperate and sub-tropical regions, but appears to be rare everywhere.
3. The sub-tertian "æstivo-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.