208 



Arthropods as Hosts of Pathogenic Protozoa 



The life cycle under favorable conditions is completed in from 

 twelve to fifteen days. These figures are of course very dependent 

 upon the temperature. The Army Commission in Cuba found that 

 the cycle might be completed in as brief a period as nine and a half 

 days. Under less favorable conditions it may be greatly lengthened. 



The adults are long lived. We have 

 seen that during the experimental work 

 in Cuba specimens were kept in cap- 

 tivity for sixty-nine and seventy-one 

 days, respectively, and that they were 

 proved to retain their infectivity for at 

 least fifty-seven days. Dr. Guiteras 

 subsequently kept an infected adult for 

 one hundred and fifty-four days. 



Low temperatures have a very great 

 effect not only on development, but on 

 the activity and even life of the adults. 

 Long before the method of transmission 

 of yellow fever was discovered it was well 

 known that the epidemics were brought 

 to a close by heavy frosts, and it is now 

 known that this is due to the killing of 

 the mosquitoes which alone could spread 

 the disease. 



Aedes calopus has a very wide distri- 

 bution since, as Howard says, being a 

 domestic mosquito, having a fairly long 

 life in the adult stage, and having the 

 custom of hiding itself in the most ingen- 

 ious ways, it is particularly subject to car- 

 riage for long distances on board vessels, 

 in railway trains, even packed in baggage. In general, its permanent 

 distribution is from 40 degrees north latitude to 40 degrees south 

 latitude (Brumpt), in a belt extending around the world. In the 

 United States it breeds in most of our Southern States. 



Thus, as in the case of malaria, there are many places where the 

 insect carrier is abundant but where yellow fever does not occur. 

 Such, for instance, are Hawaii, Australia and Asia. An outbreak may 

 occur at any time that a patient suffering from the disease is allowed 

 to enter and become a source of infection for the mosquitoes. In 



135&. Aedes calopus; larva, (xy). 

 After Howard. 



