STEGOMYIA FASCIATA AND ITS RELATION TO YELLOW FEVER 545 



found Stegomyia fasciata resting under bushes, in open fields, or in the 

 woods; this fact explains the well-founded opinion that yellow fever is 

 a domiciliary infection. 



The question of hibernation in the larval stage is important. Agra- 

 monte failed to get larvae that could resist freezing temperature, and 

 found that in the case of Stegomyia fasciata this degree of cold was 

 invariably fatal. 



The possibility of their being capable of life outside their natural 

 element must also be considered from an epidemiological point of view. 

 The dry season in the countries where this species seems to abound is 

 never so prolonged as completely to dry up the usual breeding places. 

 Experimentally, adult larvae removed from the water and placed over- 

 night upon moist filter paper could not be revived the following morning. 



The question of the life period of the female insect is of the greatest 

 importance when we come to consider the apparently long interval 

 which at times has occurred between the stamping out of an epidemic 

 of yellow fever and its new outbreak without introduction of new cases. 

 The fact is that Stegomyia fasciata is a long-lived insect; one individual 

 was kept by Agramonte in a jar through March and April into May for 

 seventy-six days after hatching in the laboratory. 



It was definitely shown by the experiment of the Army Medical Board 

 upon non-immune persons that a period of at least twelve days at a 

 temperature of about 83 F. was necessary before the infected insect 

 could transmit the germ of yellow fever from the sick; later on a mos- 

 quito which reached the age of seventy days, in the hands of Dr. Carroll, 

 was able to produce a case of yellow fever by stinging an American 

 soldier fifty-seven days after it became infected. 



These mosquitoes bite principally in the late afternoon, though they 

 may be incited to take blood at any hour of the day. They are abundant 

 from March to September, and even in November Agramonte was able 

 to capture them at will in his office and laboratory. 



The mosquito is generally believed to be incapable of long flights 

 unless very materially assisted by the wind. At any rate, the close study 

 of the spread of infection of yellow fever shows that the tendency is for 

 it to remain restricted within very limited areas, and that whenever it 

 has travelled far beyond this the means afforded (railway cars, vessels, 

 etc.) have been other than the natural flight of the insect. 



Experimentally, it has been found that the infected mosquito must 

 be kept at about 80 to 85 F. for twelve days after having bitten a yellow 

 fever patient. This is necessary in order to enable the parasites to per- 

 form the evolutions in the body of the mosquito that will render them 

 capable of reproducing the disease. In winter insects kept at this 

 temperature have failed to infect even after eighteen days. 



Experiments have demonstrated that not all mosquitoes which bite 

 a yellow-fever patient become infected, but that of several which bite 

 at the same time some may fail either to get the parasite or to allow its 

 later development in their body. This condition is similar to that seen 

 in Anopheles, with regard to malaria, j 



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