1.An epidemic of 201 cases of yellow fever of the jungle type without Aëdes aegypti, on the Planalto of Matto Grosso, Brazil, was studied during the two seasons of 1934 and 1935.
2.The identity of the disease as yellow fever was established by clinical observation, by autopsy, by the protection test, and by the transfer of infection from early human cases directly to white mice. The definite date of acquisition of immunity was determined in fifteen cases by the observation of negative protection test results on sera obtained before the onset of illness or early in the course of the disease followed by positive protection test results on convalescent sera.
3.Protection test survey results suggest that the outbreak studied did not originate from immediately preceding urban outbreaks of Aëdes aegypti-transmitted yellow fever; towns with aegypti showed negative or very low immunity rates for children. High immunity rates among Indians suggest this outbreak was probably part of Amazonian jungle endemicity.
4.The paucity of human population in the infected district and the scatter of cases in both time and space, together with the isolated circumstances attending many cases argue against man being the only vertebrate host involved.
5.The sera from five Cebus monkeys captured for this study in known infected districts all gave positive protection test results, indicating immunity naturally acquired in the jungle.
6.The immunity survey of the infected area revealed more than half of the cases discovered. Rural immunity rates were higher than village rates, and rural rates rose as the proximity of house to fields and jungle increased.
7.All available evidence points to infection occurring either in clearings next to uncleared jungle or in the jungle itself, especially during the working hours.