1.An epidemic of dengue of unprecedented proportions originating in Galveston in June, 1922, spread over all of eastern and central Texas, and into neighboring states. Between 500,000 and 600,000 cases were estimated to have occurred in Texas.
2.The organism of dengue, shown by previous workers to be a filtrable virus in the blood plasma, has been suspected of being a Leptospira on account of a supposed relationship of the disease to yellow fever. This relationship we believe to have been over-emphasized.
3.Dark field examinations of blood smears, inoculations into guinea-pigs, mice and monkeys, and attempts to cultivate the organism in media used for Leptospirae, have all given negative results.
4.Negative findings in blood, in inoculated animals (particularly guinea-pigs), and in cultures; the usual absence of liver and kidney involvements; the fact that the relationship of dengue to yellow fever has been overemphasized; and the viability of the virus in blood kept in an ice chest after removal from the host (according to Cleland, Bradley and MacDonald) lead us to believe it improbable that the organism of dengue is a Leptospira.
5.Previous experimental work and epidemiological evidence point to Aëdes aegypti (-Stegomyia fasciata) as the principal transmitter of dengue, this species being replaced principally by Aëdes (Stegomyia) scutellaris in Formosa. Culex quinquefasciatus (fatigans) has been incriminated on very slender evidence. The Texas epidemic was accompanied by an unprecedented scourge of Aëdes aegypti, and the epidemiological evidence points very strongly to the agency of this mosquito in transmission, and suggests that Culex quinquefasciatus played a very minor part, if involved at all.
6.Transmission experiments carried out with Aëdes aegypti were successful in 4 out of 6 cases; the mosquitoes succeeded in transmitting the disease in from twenty-four to ninety-six hours after feeding on patients in the second to fifth days of the disease.
7.The incubation period in experimentally infected cases, both when bitten by infected mosquitoes and when inoculated with a patient's blood, varied from four days and two hours to six days and twelve hours.