A serological survey for hemagglutination - inhibition antibodies to arbovirus was carried out on 516 residents of the rural and urban zones of the Ribeira Valley, Brazil, a largely forested area where there recently occurred an encephalitis epidemic attributed to Flavivirus Rocio. It was discovered that 24.2% of the sample population presented HI antibodies (11.2% against Alphavirus, 13.2% against Flavivirus, 4.6% against the Caraparu virus and 0.8% against other arboviruses). Neutralizing antibodies for Eastern equine encephalitis, St. Louis encephalitis and yellow fever virus were detected in some of the people, not vaccinated against yellow fever, who have always lived in the region. These last two viruses have never before been isolated in the area. The characteristics of people who presented antibodies suggest that the transmission of arboviruses has been going on for a long time, in and outside the forested area, in at least nine districts of the region. Men, and especially fishermen, among other professions, who generally work in the evening and at night, present the highest risk of infection.
Hemagglutination inhibition tests; Arboviruses Serological surveys
