An epidemic of jungle yellow fever was investigated in November and December, 1954, and early 1955, in the Oriboca Forest about 20 km distant from Belém, Pará, Brazil. The virus was isolated from ten persons all of whom were employed in opening trails in a virgin forest.
A second epidemic was studied near the village of Apeu about 60 km east of Belém in April and May of 1955. Yellow fever virus was isolated from 11 cases.
A comparison of the acute and convalescent sera of all 21 cases showed a significant rise in antibody titer for yellow fever virus.
Four strains of yellow fever virus were isolated from mosquitoes caught in the Oriboca Forest at the time of the jungle epidemic.