West Nile virus in north-eastern Italy, 2011: entomological and equine IgM-based surveillance to detect active virus circulation.

The research focuses on detecting the circulation of the West Nile Virus (WNV) in northeastern regions of Italy using surveillance procedures that incorporate both the examination of horses for antibodies and the analysis of mosquito species.

Study Background

• The study was conducted due to the continual occurrence of the West Nile Virus (WNV) in several Italian regions since 2008, indicating a potential endemic situation in these areas.
• In response to this situation, a novel plan was executed in 2011 to detect the virus in areas of northeastern Italy – Veneto and Friuli Venezia Giulia – where the virus had previously made an appearance, as well as in areas within proximity.

The Methodology

• From July to November 2011, a total of 1880 blood samples from 521 horse establishments underwent screening via a commercial assay (IgM capture ELISA) meant for antibody detection and used as an indicator for recent infections.
• Mosquitoes were also trapped in 61 different areas in the two regions using CDC-CO2 traps, a method known for its effectiveness in capturing the insects.
• The mosquitoes were categorized, combined by date/location/species and tested with real-time RT-PCR and sequencing to identify the presence of the West Nile virus.
• Alongside these proactive methods, passive surveillance was conducted on horses showing clinical symptoms and on non-migratory birds found dead.

Study Findings

• 29 horse establishments (19 initial and 10 from closer inspection around the initial premises) showed the presence of IgM sero-positives, indicating an active WNV infection.
• A total of 85,398 mosquitoes across 15 species were collected and gathered into 2732 groups. Of these, five groups of Culex pipiens mosquitoes were found to carry the WNV.
• Among the 82 birds tested from passive surveillance, only one dead collared dove was found to be carrying the virus.
• The strain of the virus belonged to lineage 2, which was detected in Italy for the first time during 2011. This strain of the virus is accountable for severe neurological diseases in humans and horses.
• By October’s first week, nine human cases of WNV infection were also confirmed in the same area.

Conclusion

Applying a combined approach for early detection of WNV, such as IgM screening in horses and examination of mosquito vectors, proved to be effective. This strategy can assist in predicting potential outbreaks and implementing control measures in a timely manner.