Further evidence for the transmission of Mansonella ozzardi by Simulium amazonicum in Brazil.

The transmission of Mansonella ozzardi was studied in two rubber collecting villages on the River Purus, state of Amazonas, Brazil. Haematophagous insects were collected from human and bovine baits during the day and night: 687 Mansonia amazonensis and 154 Culicoides sp. indet. were free from infection with M. ozzardi. The former species is probably not a vector, but the low numbers of culicoides dissected preclude any determination of its vector status. Thirty-five (0-99%) of 3530 Simulium amazonicum dissected were found naturally infected with larvae of M. ozzardi. Two hundred and ninety-nine M. amazonensis and 280 S. amazonicum were experimentally infected with M. ozzardi by feeding on volunteers. Microfilariae were detected in the blood meals of both species but no developing larvae were found in the thoracic muscles of M. amazonensis, confirming its non-vector status; 7-1% of the S. amazonicum dissected had filarial larvae in the thorax. There was a statistically significant difference between this rate and the natural rate of infection in this region, verifying that penetration of the thoraric muscles by M. ozzardi had occurred in the experimental infection. The data confirm the observation of Cerqueira (1959) that S. amazonicum transmits M. ozzardi in Brazil.