An epidemic of yellow fever in central Brazil, 1972-1973. II. Ecological studies

Results of ecological studies undertaken during the 1972-1973 epidemic of yellow fever (YF) in Goias State, Brazil, suggest that mosquitoes of the genus Haemagogus were the only vectors infected with YF virus. Nine isolations of the agent were made from 1,688 Haemagogus spp. caught within or near forests from 27 January to 3 March 1973. Seven of these isolations came from mosquitoes collected on the forest floor. No YF virus isolation was made from 791 Haemagogus leucocelaenus or 1,096 Sabethes chloropterus. Haemagogus were caught both in and outside houses located 500 m from the forest, although at a lower rate than in the forest. Haemagogus collection rates in a secondary growth forest were similar to or even higher than those in primary forests. YF virus was recovered from a Cebus monkey and hemagglutination-inhibition and/or neutralizing antibody to YF virus was found in seven (30.4%) of 23 primates examined. There was, however, little evidence of sick or dying monkeys. Among other wild-caught animals only a single marsupial (Caluromys) had antibodies to the virus. These data show that sylvan YF is not confined to the forest, nor always associated with conspicuous epizootics.