Epidemiological investigations of an outbreak of Mayaro (MAY) virus which occurred in the rural village of Belterra, Pará, Brazil are reported. Human cases were first recorded in December 1977 and continued through June 1978. Approximately 20% of the more than 4,000 persons resident in Belterra were infected, and a very high proportion of those infected suffered overt clinical illness. Cases were identified in all areas of Belterra and among all age groups; however, the greatest number of cases was seen among those who resided in close proximity to the forests. Yellow fever (YF) virus was also active in Belterra concurrently with the MAY virus outbreak. Six human cases of YF were identified, of which five were fatal. The YF outbreak ended following YF vaccination of the human population.
Present address: Gorgas Memorial Laboratory, APO Miami 34002.