This study was undertaken to investigate the prevalence of Mansonella ozzardi
infection and to estimate the parasitic infection rate (PIR) in simuliid black flies in the municipality of Pauini, Amazonas, Brazil. We used thick blood films to examine 921 individuals in 35 riverine communities along the Pauini and Purus Rivers. Simuliids were caught in several communities. Flies were identified, stained with haematoxylin and dissected. Overall, 44 (24.86%) of 177 riverines were infected in communities on the Pauini River and 183 (24.19%) of 744 on the Purus. The prevalence was higher in men (31.81% and 29.82%) than in women (17.98% and 19.18%) and occurred in most age groups. The prevalence increased sharply in the 28-37 (50% and 42.68%) age group and increased in the older age classes. The highest prevalence was in farmers (44% and 52.17%, respectively) in the Pauini and Purus Rivers. Only Cerqueirellum amazonicum
(Simuliidae) transmits M. ozzardi
in this municipality, and we found a PIR of 0-8.43% and infectivity rate of 0-3.61%. These results confirm that rates of M. ozzardi
infection are high in Pauini and suggest that its prevalence may be far greater than has been previously reported due to the absence of a program for treating the population.