PUBLIC HEALTH 



17 



Like malaria, dengue is tropicopolitan in range, and extends 

 only into the warmer parts of the south. Here it sometimes 

 appears in extensive epidemics, but in a much more erratic 

 way than malaria, which has the well-deserved rei)utation 

 of appearing year in and year out in the same districts. This 

 difference is probably due to the absence of chronic human 



Fro. 6. Distribution of CuUx quinquefaseiaitu in the United States. 



carriers and the fact that Culex quinquefasciatus does not 

 breed in permanent water, but is an almost truly domesti- 

 cated species which breeds in temporary water near human 

 habitations, and under the climatic and other conditions of 

 our country does not find anything like uniform opportunities 

 for breeding from one season to another. In consequence of 

 their separate breeding grounds, measures designed to con- 

 trol malarial mosquitoes have no effect or practically none 

 upon the dengue mosquito. It must be dealt with mainly 

 by education leading to individual effort and cooperation in 

 communities. Aside from its pathogenic possibilities, this 

 species is a rather persistent biter, which is another argument 

 for its control. 



The same Culex quinquefasciatus has been shown to be at 

 least partly responsible for the transmission of a parasitic 

 disease of the tropics known as filariasis. The direct cause 

 is a nematode worm belonging to the genus Filaria which is 

 present in the circulation and lymphatics of the infected 



