366 DISEASES OF UNCERTAIN ETIOLOGY 



in 1495, in ihe island of St. Domingo. These Spanish troops carried 

 it to America. 



It is endemic un ihe east coast of Mexico, Central and South America 

 as far as Rio de Janeiro, and the Antilles. Also in Guatemala, Spanish 

 Honduras, Nicaragua, Costa Rica, Labrador, French Guiana, Dutch 

 Guiana, Ecuador and along the rivers Magdalena, Orinoco and 

 Amazon. 



The true home centre is Central America and the West Indies. 



It was formerly common but now is extinct on the Isthmus of 

 Panama. 



Since 1905, eleven cases have been, d^ected and isolated by the 

 Canal Zone authorities. 



These cases came from Cartagena, Guayacjuil and Buenaventura. 



The epidemic of 1635 to 1690 affected Guadeloupe, Cuba, Jamaica, 

 San Domingo, Martinique and Vera Cruz. 



West Africa has probably been a second endemic centre since 1520, 

 when the Cape \>rd Islands and the Gulf of Benin had an epidemic. 



From these endemic centres ships carr}- the disease to 46° 56' X., 

 and 34° 54' S. Towards the North the disease becomes milder but 

 towards the South it may become very severe. 



England, Swansea, was attacked in 1S65 but it died out. 



France was attacked in 1861. 



Madrid in Spain, in 1878. 



The distribution seems to coincide with that of the mosquito, S. 

 calopus. 



This is supported by the fact that : — 



The disease is endemic in warm climates. 



It increases in the summer and disappears during the winter in 



temperate climates. 



It is carried by ships. 



It affects low-lving parts of the coast, especially (he insanitary 



districts. 



An atmospheric temperature of over 75° F. is required for its active 

 propagation. Towns upon the sea coast, banks of rivers and near 

 deltas are often infected. 



The disease follows lines of communication. 



In Rio de Janeiro visitors maintain the disease. 



Long residents in an infected district tend to become immune. 



AETIOLOGY. 



The causative organism is an ultra-microscopic, non-filtrable virus, 

 because : — 



o'l c.c. of infected blood will reproduce the disease in a non- 

 immune person. 



