DENGUE IN INDO-CHINA. 27 



There are no differences between the naval regulations for Annamese 

 and European sailors. 



In shorty 12.96 per cent of the Europeans escaped infection in 1907 

 and 100 per cent of the Annamese; in 1906 the Annamese again escaped 

 infection while but 10.3 per cent of the Europeans were not attacked. 



The natives of the MancJie were questioned one by one with the 

 greatest care; they declared that they did not remember ever having 

 had, at any time, a like disease either on board or at home. If these 

 declarations are worth anything, it must be admitted that the Annamese 

 have not the same susceptibility as the French, or else that dengue is a 

 disease so common in the country that repeated light attacks have 

 protected them. It is this latter hypothesis that has been adopted in 

 order to explain the immunity of negroes to yelloW fever. 



It is also interesting to consider the reasons why some of the Euro- 

 peans escaped the epidemic of 1907. Their number was so small that an 

 individual inquiry was possible. Those which escaped were 4 officers 

 and 10 sailors. 



Inquii*y developed the fact that two out of the four officers had 

 already had dengue on the same boat in 1905. As to the other two, 

 they had previously taken part in a hydrographic mission off the coast 

 of Madagascar, where epidemics of dengue are by no means rare. (See 

 Vincent.) Their immunity was probably gained while at that station. 

 As to the sailors who escaped dengue in 1907, three had served at 

 Madagascar, one in the Senegal and in China, one in Guiana, and one 

 at Saigon. The last two had already contracted dengue, one on the 

 Manche in 1906, and the other on the Eersaint. 



The susceptibility of the French in comparison with that of the 

 Annamese has been amplj' demonstrated by the above considerations. 

 All the young French sailors (100 per cent), the crew being almost 

 entirely composed of these, were affected; we further observed that in 

 four different instances a previous attack had given immunity for froili 

 one to two years. The immunity of the other cases seems to depend 

 somewhat upon former visits to dengue infected countries, where attacks 

 have either passed unrecognized, or been taken for malaria. 



SYMPTOMATOLOGY. 



The disease begins, in general, very abruptly, either in the morning 

 on wakening, or in the course of the day, during work. The patient 

 feels a violent headache in the region of the forehead and around the 

 eye sockets, sometimes he is so dazed that he scarcely can stand upright. 

 The fever rises almost immediately. Sometimes it mounts at once to 

 39°. 5 or 40° or more, sometimes it does not at first exceed 38°. 5, but 

 rapidly increases to 40°. In some instances the attack is less sudden, the 

 patient only coming into the hospital in the afternoon, having felt ill 



