Mosquito control districts in Indiana and the US monitor mosquitoes for important human diseases such as West Nile. Monitoring involves collecting mosquitoes then performing a genetic test for the presence of the pathogen DNA.
A variety of traps may be used to collect mosquitoes including the gravid trap developed by the CDC. The CDC Gravid Trap attracts female Culex mosquitoes searching for an oviposition site. The trap uses as cage suspended over a tub. Water containing hay can produce an attractive oviposition site for Culex females. As females investigate the hay infusion, they are sucked into the trap where they can be collected for analysis. This trap is useful because it primarily captures female mosquitoes that have previously fed and thus provide a measure of the prevalence of virus in their bird hosts.
Mosquito districts can intensify mosquito control efforts if the number of infected mosquitoes increases.