# Orthoflavivirus nilense surveillance in the State of Piauí, northeastern Brazil

## TL;DR

This study investigates the presence of West Nile virus in birds, mosquitoes, and horses in Piauí, Brazil, but finds no evidence of the virus in collected samples.

## Contribution

The study contributes new data on WNV surveillance in Brazil and highlights challenges in detecting the virus in healthy animals.

## Key findings

- No positive WNV samples were found in birds, mosquitoes, or equids from 11 municipalities.
- The lack of detection may be due to the difficulty of molecular detection in healthy animals and delayed human diagnosis.
- Serological surveys in asymptomatic animals are recommended in areas with late human diagnoses.

## Abstract

The cycle of the Orthoflavivirus nilense (West Nile virus - 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 State.

To investigate the presence of WNV in birds, mosquitoes, and equids in municipalities of Piauí.

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.

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.

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.