Potential vectors of West Nile virus following an equine disease outbreak in Italy.

The research details an investigation of the likely vectors of the West Nile Virus (WNV) after an outbreak in horses in central Italy, during the period of 1999-2002. It studies the mosquito populations of the area, focusing on their numbers and behavior, to draw conclusions about their potential roles in transferring the virus to horses and possibly humans.

Research Context

• The paper documents an investigation following an outbreak of equine encephalomyelitis (WNV-related illness) among race horses in Tuscany, Italy, in 1998. The outbreak occurred across four provinces: Firenze, Lucca, Pisa, and Pistoia, including the largest inland marsh in Italy – the Fucecchio wetlands – and adjacent Cerbaie woodlands where horse breeding occurs.

Research Methodology

• Entomological surveys were undertaken in the Fucecchio and Cerbaie areas from 1999 to 2002 to identify potential vectors for the WNV transmission. The team collected mosquito larvae from breeding sites and adult mosquitoes using various sampling methodologies.
• A total of 6023 mosquitoes were collected, out of which 11 species were identified. No viruses were isolated from 665 of the processed mosquitoes.

Observations and Findings

• In the Fucecchio marshes, the Culex impudicus mosquito species was the most abundant, peaking in spring and autumn. It was noted that their highest presence in early spring coincides with the arrival of migratory birds from Africa.
• In the Cerbaie hills, the most common species was Culex pipiens, with its population peak in late summer.
• Though no viruses were isolated from the mosquitoes processed, the data collected suggested possible modes of WNV transmission involving these two Culex species in the studied locations.

Implications and Conclusion

• The study suggests that the Culex impudicus, partly ornithophilic, could possibly transmit WNV from migrating to non-migrating birds during springtime, given its peak population coinciding with the migration period.
• On the other hand, Culex pipiens, with a broader host range and peak population in late summer, is hypothesized to be the likely vector transmitting WNV from birds to horses and possibly humans.
• This research adds to the understanding of WNV transmission patterns in regions with similar ecosystems and can guide future preventative measures to contain WNV outbreaks in such areas.