207 



Both infections may occur in the same locality. At Aden, 

 in 1893, the summer outbreak of Phlehotomus fever was followed 

 by one of dengue in the autumn. No immunity was aiforded by 

 the former infection against the latter; whole families were 

 seized ; papular or urticarial rashes broke out in most cases. The 

 author himself was attacked at this time, and in his case joint 

 pains were severe — much more so than in PJtlebotomus fever — 

 and the initial rash was accompanied by itching of the palms 

 and soles. 



Aberrant cases of dengue, and they occur in every epidemic, 

 closely resemble sand-fly fever. Moreover the late eosinophilia 

 observed by Balfour in Khartoum, by Harnett in Calcutta, and 

 by others,' also occurs in sand-fly fever, so that the infections 

 cannot be separated by microscopical examination of the blood. 



Graham, of Beyrout, was the first to investigate dengue experi- 

 mentally. After feeding Culex fatigans on dengue patients, he 

 caused them to bite susceptible people residing in places where 

 the disease was absent. He thus transmitted the infection to 

 six persons. He also induced the disease by inoculating a man 

 with an emulsion of the salivary glands of an infected Culex. 

 In 1906 Ashburn and Craig ascertained that the blood of dengue 

 patients was infective, and that the virus passed through a filter 

 which was impervious to the Micrococcus melitensis. Infection 

 has also been conveyed once by infected Stegomyia. 



Til ere are considerable dift'erences in the infectivity of the 

 virus in sand-fly fever and in dengue. Blood extracted after 

 the first twenty-four hours in the course of sand-fly fever no 

 longer can excite the disease. It has failed to do so in every 

 attempt (five experiments made). The blood of dengue patients 

 with which the successful inoculations were performed was 

 drawn off on the second to the fifth days of the disease. 



Whereas Phlehotomus are not capable of transmitting sand- 

 fly fever until six days after feeding on a patient who is in the 

 first day of his illness, dengue has been conveyed by mosquitos 

 immediately after their meal of dengue blood; nevertheless the 

 virus survives in them, for they have conveyed the disease eight 

 to twenty-seven days after feeding on a dengue sufferer. 



Graham protected families from dengue by means of mos- 

 quito curtains. E. H. Ross extinguished epidemics of dengue 

 which had been of yearly occurrence in Port Said by exterminat- 

 ing mosquitos. Evidence is accumulating that Stegomyia is an 

 agent in the propagation of dengue. Legendre concludes from 

 a study of an extensive epidemic of this disease at Hanoi in 1910 

 that this mosquito was the responsible vector, since the outbreak 

 was coincident with a great increase in their numbers, while 

 other species were few. 



There is a close resemblance between dengue, sand-fly, and 

 yellow fever infections; they are all caused by some virus which 

 circulates in the blood, and is capable of passing through a filter 

 which retains bacteria ; the onset of the fever is similar in many 

 instances, and during the first forty-eight hours of the illness it 

 may be impossible to distinguish between the infections; even 

 later a diagnosis on clinical grounds may be unattainable, for 



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