1104 



PATHOGENIC PROTOZOA 



tions may occur at any time ; while in the sub-tropics and temperate 

 regions it is a seasonal disease, appearing soon after the onset of hot 

 weather with its new crop of anophelines and continuing until the 

 first cold weather which destroys most of the infected mosquitoes. 

 It is possible that the disease may be carried over from season to 

 season by the hibernating mosquito although definite proof of the 

 importance of this is lacking. It is carried over to the next season 

 by the human carrier, in whom the disease may be latent or who may 

 have suffered from clinical relapses throughout the year. Modern 

 times have seen it disappear from many regions where it was formerly 



N$^!c^0 



FIG. 149. PLASMODIUM VIVAX 

 (Army Med. School Collection, 

 Washington, D. C.) 



FIG. 150. PLASMODIUM VIVAX. (Gamete.) 

 (Army Med. School Collection, Washing- 

 ton, D. C.) 



endemic, because of increased cultivation of the soil and better surface 

 drainage, as, for example, in England and the Ohio river valley. 



In the registration area of the United States there were 1565 

 deaths from malaria in 1913 ; in Italy, up to 1900, the average number 

 of deaths from this cause annually was 16,000. One cannot obtain a 

 true picture of the importance of the disease, however, from mortality 

 statistics, since it is not often fatal, and the morbidity is out of pro- 

 portion to the mortality. In many villages, where it is endemic, one- 

 third to one-half the population may have parasites in the blood, most 

 of them without clinical symptoms, yet they are not able to work and 

 the children remain undeveloped and backward. Much of the illness 

 attributed to hookworm infection is, in reality, due to latent malaria. 



