DENGUE AND MOSQUITOES 303 



five generations in France under conditions that exist about houses, but the 

 German experiments show that it is unlikely that this species can produce even 

 a generation under the natural conditions of the climate at Hamburg. 



DENGUE. 



This disease frequently appears in epidemic form throughout the tropics and 

 subtropical regions. It is marked by sudden appearance, acute fever, short 

 duration and comparative benignity, fatal cases being extremely rare. Dengue 

 has been confused with influenza and various febrile diseases and its existence 

 as a disease entity has even been denied. However, it is now generally recog- 

 nized as a specific disease. Considering the fact that dengue has been com- 

 paratively little studied, its mosquito-bom character may be said to be fairly 

 well established. Ashburn and Craig point out that attention has been directed 

 repeatedly to the resemblance between dengue and yellow fever and that it is 

 well founded in fact. Craig has recently shown, as will be seen in the following, 

 that, like yellow fever, this disease is caused by an organism of ultra-microscopic 

 size, almost certainly a protozoan and closely related to the causative organism 

 of yellow fever. 



Harris Graham, of Beirut, in 1902, was the first to point out that dengue is 

 not contagious, but is due solely to the agency of mosquitoes. In a second paper, 

 in 1903, he specified the common house-mosquito of the tropics (Culex quin- 

 quefasciatus) as the responsible species and this has been experimentally con- 

 firmed by some of the later investigators. 



Graham was led to investigate the possibility of mosquito agency in the 

 propagation of dengue through the fact that at Beirut, where there was a very 

 extensive epidemic, mosquitoes were excessively abundant, while certain high 

 and dry mountain villages where there were no mosquitoes remained free from 

 the disease. From the previous history of the disease he made the following 

 deductions : 



" There is great multiplicity of evidence to show that it does not spread to any 

 extent when carried away from certain low-lying regions, which are its favorite 

 abode. Epidemics in Cuba, Jamaica, East Indies, Reunion, Martinique, and 

 Madagascar, all seem to show that, in spite of the most active communication, 

 dengue cannot spread to any extent when carried into dry and high places in the 

 interior. These epidemics have shown time and again that people come down 

 from these higher and drier places, contract the disease, and then have it break 

 out on them in their homes to which they have returned, and there lie smitten 

 with it for several days without the other inmates of the household catching it." 



Graham went to work to prove experimentally the transfer of dengue by mos- 

 quitoes. A mother suckling her child became ill with dengue. As soon as the 

 diagnosis was made, wire screens were put in all the windows of the house, and 

 the mosquitoes in the interior were all destroyed. These precautions were con- 

 tinued until the 10th day after recovery. The infant did not cease to nurse and 

 remained constantly in its mother's arms, yet it did not take the disease. In 

 another case one of four children was attacked by the disease. The room was 



