l82 YELLOW FEVER [CH. 



Geographical distribution. In considering the distribution 

 of yellow fever it is necessary to emphasize the fact that the 

 disease is being rapidly eradicated from the more civilized 

 regions of the world, and comparatively few endemic centres 

 exist at the present time. 



The most important of these are the following : 



Guatemala, Nicaragua, Costa Rica, Ecuador, Spanish 

 Honduras, Venezuela, French Guiana, certain parts of Mexico 

 and the West Indies, and along the banks of the Amazon, 

 Orinoco, and Magdalena Rivers. It will thus be seen that the 

 States of Central and South America are the great centres of 

 the disease, and from these regions it has spread into many 

 other countries. It is probably endemic in West Africa for the 

 continual recurrence of small epidemics cannot be explained on 

 the supposition that these represent infections introduced by 

 ships. 



The endemic centres of yellow fever do not extend beyond 

 latitudes 40 N. and 40 S., where the mean isotherm is not 

 below 26 C. The malady, however, often extends into colder 

 regions during the summer months, and may produce great 

 epidemics, which, however, always disappear on the return of 

 cold weather. 



Great epidemics of yellow fever have occurred in many of 

 the seaport towns of the Southern United States, especially 

 in New Orleans where, in 1878, there was a record of 4046 

 deaths as the result of one epidemic. The Gulf ports were 

 probably endemic centres during the eighteenth century and 

 first half of the nineteenth, but as the result of improved 

 hygienic conditions and better drainage the breeding places 

 of the mosquitoes have been reduced until now the disease is 

 almost extinct. 



The Atlantic ports, as far north as New York, were also 

 frequently visited by more or less severe epidemics, as the 

 disease was continually being introduced by ships coming 

 from Cuba and other endemic centres. The infected Stegomyia 

 carried from these places would be able to live on board for 

 some weeks and thus be capable of spreading the infection at the 

 ports at which the ship called. 



