Oropouche virus transmission in the Amazon River basin of Peru.

Seroepidemiologic studies were conducted to determine the prevalence of Oropouche (ORO) viral antibody, risk factors, and the incidence of infection among residents of the Amazon region of Peru. Blood samples, as well as demographic, cultural, and medical history data, were collected from residents in a sector of the city of Iquitos and in an adjacent rural and three neotropical rain forest communities. Blood specimens were obtained approximately one year later from a cohort of the same study subjects who were negative for ORO antibody on the initial cross-sectional survey. Sera were tested for ORO IgG antibody by an enzyme-linked immunosorbent assay. Antibody prevalences were 35% for residents of the urban population, 24-46% for the forest communities, and 18% for the rural community. Antibody prevalence increased with age, and subjects who were seropositive were significantly (P = 0.001) older (mean = 33 years) than the seronegative subjects (mean = 15 years). Multivariate analysis revealed that only age, urban and forest residence, and occupation as a farmer or housekeeper remained significantly associated with seropositivity. Seroconversion data for the same populations one year later demonstrated evidence of ORO viral infection among 28% of the residents in the rural community and 2% or less in the forest and urban communities. Oropouche virus infection was significantly associated with older age (P = 0.04) in the rural community (P < 0.001). These data support prior evidence of ORO viral infection among residents of Iquitos and surrounding villages and suggest that transmission of this virus occurs continuously in the population of this area of the Amazon basin.

The epidemiology of dengue virus infection among urban, jungle, and rural populations in the Amazon region of Peru.

The first confirmed outbreak of dengue fever in Peru occurred during 1990 in Iquitos, a city of approximately 300,000 residents in the Amazon region. Because of the apparent establishment of endemic transmission of this mosquito-borne viral disease following the outbreak, epidemiologic studies were initiated in 1992. Blood specimens and data on demographic, environmental, and medical history factors were collected from volunteers in an urban sector of Iquitos, in a rural area on the outskirts of Iquitos, and in three nearby jungle communities. A follow-up blood specimen was obtained approximately one year later from a sample of subjects. Sera were tested for dengue IgG antibody by an enzyme-linked immunosorbent assay, and specificity was verified using a plaque-reduction neutralization test. Dengue antibody prevalence was 66% in the urban population, 26% in the rural population, and 32-67% in the three jungle areas. A significant association was found between age and antibody prevalence, with a steady increase in prevalence from 18% among subjects less than five years of age to greater than 90% for subjects more than 50 years old. Increased antibody prevalence also was associated with urban and jungle residence and with a piped source of household drinking water. Seroconversions were documented in four of five surveyed communities. These results indicate that dengue virus transmission continues in and around Iquitos and suggest that transmission also occurred prior to the 1990 epidemic.