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International Notes Yellow Fever in the Americas, 1981 and 1982

For the years 1981 and 1982, five countries in the Americas (Bolivia, Brazil, Colombia, Ecuador, and Peru) reported 368 cases of jungle yellow fever, slightly more than the 324 of the preceding 2 years. Bolivia and Peru accounted for 84.8% (312) of the cases; Brazil, 12.5% (46); and Colombia, 2.2% (eight); two cases were detected in Ecuador. Deaths from yellow fever in those years totaled 183.

The highest monthly number of cases occurred in the first half of each year, with a peak in March. This may reflect increased rural and forest labor practices during the first months of the year among susceptible populations in yellow fever enzootic areas. Another factor may be higher densities of Haemagogus mosquitoes--the main jungle yellow fever vector in the Americas--during the rainy season.

All cases reported in 1981 and 1982 occurred in known endemic areas, except one epidemic in 1981 in Rincon del Tigre, Department of Santa Cruz, Bolivia, that accounted for approximately 50% of Bolivia's cases that year. The last confirmed outbreak in the Department of Santa Cruz occurred in the late 1940's, illustrating the virus' potential to reappear after long periods of inactivity. A 1980-1981 outbreak in Brazil involved the states of Goias, Mato Grosso, and Mato Grosso de Sul. This epidemic and previous epidemics in the State of Goias may reflect virus movement from the enzootic areas of the Amazon Region.

Age and sex data, available for 347 patients, showed that 79% (275) were male. Most patients (79%) were between 15 and 34 years of age; no patients were under 1 year; and all but one case in the 1-4-year age group occurred in the Rincon del Tigre region. All Brazilian patients were over 15 years of age. This age and sex distribution is consistent with patterns of disease acquired in the jungle.

No urban cases of yellow fever have been documented in the Americas for the past 4 decades, although several patients with jungle-acquired disease have been hospitalized in A. aegypti-infested towns during this period. Although surveillance in remote areas may be inadequate, a general decline in incidence of the disease in the Amazon Region appears to have resulted from intensification of vaccination programs throughout endemic areas. About three million doses of 17D vaccine are administered in Brazil annually (3,300,000 in 1981).

Because of continuing yellow fever incidence and the reinfestation of some infected areas, the Pan American Health Organization (PAHO) has recently convened several technical meetings to examine the problem. Recommendations from these meetings include: 1) improving surveillance activities; 2) strengthening direct cooperation among affected countries; 3) promptly disseminating information to member countries; 4) increasing production of 17D vaccine; and 5) promoting assistance among member countries, either directly or through PAHO, with bilateral loans and grants and the provision of equipment, materials, and technical advisory services. Reported in PAHO Epidemiological Bulletin 1983;4(1):1-5.

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