DENGUE 183 



over limited areas, affecting a large per cent of the popu- 

 lation. 



Nearly every fluid and organ of the body has been examined 

 in an effort to find the organism causing dengue, but although 

 many supposed parasites have been found, the true cause of the 

 disease is still unknown. In at least one stage of its life history 

 the parasite, like that of yellow fever, is ultra-microscopic. The 

 disease has been proven by experimentation to be transmitted 

 commonly by the tropical house mosquito, Culex quinquefasciatus, 

 and its distribution geographically coincides very closely with 

 that of this mosquito. However, Aedes calopus has also been in- 

 criminated, and in Formosa another closely related species, 

 Desvoidea obturbans. 



Unlike yellow fever, dengue has a very short incubation period 

 in the mosquito in one experiment it was only 48 hours. This 

 fact, together with the short incubation period in the human 

 body (from two to five days), explains the rapidity with which 

 dengue epidemics spread. 



The disease begins with startling suddenness. Within a few 

 hours a normal healthy individual acquires a prostrating fever, 

 a severe headache and terrible aches in the bones and joints 

 which make it necessary to lie still. His face and sometimes 

 his whole body becomes flushed and purple with congested blood- 

 vessels, and the patient is to say the least very miserable. In 

 a day or two the fever moderates, and usually is terminated by 

 a sudden crisis of nose-bleed and diarrhea, relieving the con- 

 gestion which has been felt in all parts of the body. Then follows 

 an interval of apparently normal condition during which the 

 patient feels perfectly well. After a "few days there is a return of 

 more or less severe fever and aches accompanied by a measles- 

 like rash. The latter fades in from three to five days and is fol- 

 lowed by a powdery scaling off of the skin. If lucky, the patient 

 now quickly recovers but more often he has lingering and recur- 

 ring aches in various joints, especially the knees and ankles, and 

 he may be thus afflicted for several weeks before final recuper- 

 ation, whence the name " breakbone fever." The disease is 

 dangerous to life only if complicated in some way. 



An attack of dengue usually confers immunity on an individ- 

 ual but this sometimes lasts only a year and is sometimes not 

 established at all, since more than one attack during a single 

 epidemic have been known to occur. 



