Orthoflavivirus nilense surveillance in the state of Piauí, Northeastern Brazil

Background: The cycle of the Orthoflavivirus nilense (WNV) involves birds and mosquitoes, while humans and equids serve as terminal hosts. In 2014, the first human case in Brazil was confirmed in Piauí. Objectives: To investigate the presence of WNV in birds, mosquitoes, and equids in municipalities of Piauí. Methods: Collections were carried out following recommendations from the Ministry of Health of Brazil, in 11 municipalities (all with human cases or bird mortality), where biological samples were collected from birds, mosquitoes, and equids. The Viral RNA extraction was performed using a commercial kit, following the manufacturers’ recommendations; samples were subjected to reverse transcription and polymerase chain reaction, with specific primers for WNV. Findings: 2,706 samples were collected (636 birds, belonging to 99 species; 420 equids, and 1,650 mosquitoes, grouped into 346 pools, totaling 18 species. No collected sample yielded a positive result, corroborating with other studies showing the difficulty of molecular detection of WNV in healthy animals, which may explain the non-detection, in addition to the delayed diagnosis in humans. Main conclusions: A local investigation involving suspected cases is still recommended in animals; however, in locations with late diagnosis in humans we suggest a serological survey of asymptomatic birds and equids.