178 YELLOW FEVER [CH. 



can exist all the year round, and in consequence only appears 

 sporadically in subtropical and temperate regions. It is 

 mainly a disease of seaport towns and practically all the great 

 epidemics have occurred in such localities. 



About the early history of yellow fever very little is 

 certain. It is said to have been known by the Aztecs under 

 the title of " Matlazahuatl." Other authorities believe that 

 the disease originally occurred in the Antilles and was carried 

 by the Spaniards to the mainland of America. There is little 

 doubt that the disease originated in America and was fully 

 established by the time that the early explorers arrived from 

 Europe. 



On the other hand certain authors have thought that it 

 might have been introduced from West Africa by the slave- 

 boats, but such a view is not in accordance with the fact that 

 the disease seems to have been already known in America when 

 Columbus discovered the continent. From Central America 

 yellow fever has been carried by ships to various parts of the 

 world, in some of which it has become endemic, and in others 

 only occurred in epidemic form. 



Its distribution is shewn in Fig. 50, which represents 

 the extreme range of all places in which yellow fever has been 

 known to occur within recent times. At present many of 

 these localities are quite free from the disease and, as a result 

 of anti-mosquito campaigns, many more are likely to become 

 so in the near future. 



At present the chief endemic foci of the disease are the 

 States of Central and South America, with the exception of 

 Panama, and the West Coast of Africa. In the United States, 

 the Gulf States have frequently been the site of great epidemics, 

 but the climatic conditions prevent the disease from becoming 

 endemic. In West Africa yellow fever seems to have been 

 known since 1778, when it was recorded from St Louis. The 

 fact that the disease has existed in an unbroken line for more 

 than a century, is strong evidence of its endemic character in 

 West Africa, and although there have been no outstanding 

 epidemics, yet the number of patients who annually succumb 

 to " Bilious Remittent Fever " is considerable. One of the 



