192 DENGUE [CH. 



Neither age, sex, race, nor social conditions, seem to have 

 any effect on this disease, which attacks rich and poor, old 

 and young, black and white, with the utmost impartiality. 



The rapid spread of epidemics of dengue is another feature 

 which was noticed even by the earliest observers. The rapidity 

 with which it extends is probably unequalled by any other 

 malady, and usually within a few days of its appearance in any 

 particular locahty a considerable proportion of the population 

 will be found suffering from the disease. In 1884 an epidemic 

 in Noumea broke out so suddenly that the majority of the 

 public services were disorganized ; a regiment of marines was 

 reduced to less than one section, and so many of the sailors 

 were affected that the ships were temporarily put out of action. 



The disease is usually conveyed from one place to another 

 by means of ships carrying infected passengers. Thus dengue 

 was introduced into Tahiti by a steamer that carried a single 

 infected passenger, who had contracted the disease in Noumea. 

 This case was sufficient to start an epidemic in the island. 



When any particular maritime locality becomes the 

 centre of an epidemic, all ships visiting the place are liable to 

 become infected. Occasionally the disease is spread by means 

 of trains as, for example, in India, where it was carried from 

 Calcutta across Bengal by these means. Such a method of 

 expansion, however, is somewhat unusual and seaports 

 continue to be the localities most visited by epidemics, the 

 infection being introduced by ships. An epidemic generally 

 lasts for about five or six months, gradually diminishing in 

 the number of cases until it finally disappears. 



It is interesting to note that the distribution of dengue 

 shews a remarkable coincidence with that of Culex fatigans. 

 (Figs. 51 and 52.) 



Causal agent. Our knowledge of dengue is still very im- 

 perfect and in spite of numerous researches the cause of the 

 disease remains unknown. McLaughlin, in 1886, found a 

 micrococcus in the blood of infected patients and supposed 

 that this was the causative agent, but his results have been 

 disproved by subsequent investigators. In 1903, Graham 

 believed that he had discovered the cause of the disease, in 



