Objective: To present a quantitative risk assessment of West Nile (WNV) virus introduction into
Barbados, West Indies.
Design and Methods: Three possible modes were considered: a) WNV infected mosquitoes via air
transport, by city of departure, b) WNV infected mosquitoes via marine transport and c) viraemic
migratory birds. We estimated the number of WNV infected migratory birds as the product of the
proportion of migratory birds infected and the number of migratory birds entering Barbados in three
taxonomic groups. We further estimated the number of days these birds would be infectious as:
We then estimated the number (#) of infectious mosquito-days for mosquitoes entering Barbados via air transport as: # infected mosquitoes = (total flights per week/city) x (duration of WNV season) x (number of Culex mosquitoes aboard each flight) x (Culex mosquito WNV infection prevalence) x (vector competence index) x (days infectious). The number of infected mosquitoes entering Barbados via marine transport was estimated using a similar expression as for air transport, except that the number of airplanes and mosquitoes/airplane were substituted with the # of sea containers during a 22-week mosquito season and # of mosquitoes/container.
Results: Migratory birds (~69–101 infected birds/year) were associated with the highest introductory
risk followed by mode (a) (~2 infected mosquitoes/year) and mode (b) (0.004 infected mosquitoes/year)
Conclusions: Migratory birds and mosquitoes via air are imminent threats for virus introduction.
Impending co-circulation of West Nile virus and four strains of dengue virus may present new challenges
for public health.