248 SANITARY ENTOMOLOGY 



DISEASES OF UNCERTAIN ORIGIN TRANSMITTED BY MOSQUITOES 



DENGUE FEVER, one of the severe fevers of the tropics, sometimes 

 called break-bone fever, occasionally occurs in the United States. It is 

 undoubtedly caused by a living organism which requires over two days 

 to reach the stage necessary to produce the symptoms of the disease when 

 inoculated into human beings. It is so small that it will pass through the 

 pores of a filter which will retain Micrococcus melitensis, which is only 

 0.4 micron in diameter. This minute organism is taken up by mosquitoes 

 and transmitted to man. Graham-Smith and Ardate have observed small 

 bodies in the red blood corpuscles, which are described as small, usually 

 round, but sometimes elongate, bodies about one-fifth to one-third of the 

 size of a red corpuscle. They divide up into minute granules, which 

 become extra-corpuscular, and complete a cycle of schizogony. Graham 

 (1903) fed Cvlex quinqitefasciatus Say (fatigans Wiedemann), on dengue 

 patients and claimed to have found his organism in the mosquitoes up to 

 the fifth day after feeding. He succeeded, after an incubation period 

 of four to six days, in infecting healthy people by the bites of mosquitoes 

 fed on dengue patients in two series of experiments, claiming the trans- 

 mission to be due to the Culex, but he states that Aedes argenteus Poirret 

 {Stegomyia fasciata Fabricius) were present in many if not all of his 

 experiments. Ashburn and Craig (1907) in the Philippines also claimed 

 to have proved transmission by the bite of the same mosquito, but Cleland 

 and Bradley (1918) challenge the results of both these investigations. 

 Nevertheless, Bancroft (1906) conducted experiments obtaining two 

 apparently successful cases of transmission of the disease by Aedes 

 argenteus, ten and twelve days after these had bitten dengue patients, 

 while in the three failures the test patients were bitten fifteen, fifteen and 

 seventeen days after the mosquitoes fed on individuals suffering from 

 dengue. 



Observations made by Legendre in Hanoi led him to suggest Aedes 

 (Stegomyia) as probably a carrier of the virus. 



Cleland, Bradley, and McDonald (1918, 1919) conducted extensive 

 experiments (1918) with both Cvlex quiriquefasciatus (fatigans) and 

 Aedes argenteus (fasciata) and obtained positive results with the latter 

 in four out of seven tests, and negative results with the former in two 

 tests. The mosquitoes after biting dengue patients were conveyed to dis- 

 tricts where dengue fever did not exist. The incubation period in man in 

 these cases was from six to nine and a half days. Later experiments 

 (1919) corroborated this work. 



Poliomyelitis was experimented on with negative results by Howard 



