225 - Looking for Life in the Margins: Enhanced surveillance in an outbreak of locally acquired malaria

Abstract: The 2023 locally acquired outbreak of Plasmodium vivax malaria in Sarasota County, Florida occurred at Manatee County's southern border and resulted in a robust, integrative mosquito control response from Manatee County Mosquito Control District (MCMCD). Autochthonous malaria had not occurred in Florida for 20 years. The malaria parasite can only be carried by female mosquitoes of the Anopheles genus yet, in the absence of malaria cases, stateside mosquito control operations may not find the genus pestiferous enough to warrant major focus, let alone routinely employ anopheline-specific collection methods. MCMCD enhanced its surveillance to supply Anopheles specimens requested by the Florida Department of Health for testing. With a minimum of bi-weekly visits, adult female Anopheles specimens were collected via CDC light traps and downdraft UV light traps both using CO₂ attractant as well as various iterations of resting containers. Trap placement was adaptive to new case information and proximity to areas used by un-housed persons. A total of 418 specimens of the Anopheles genus were collected over 38 trap nights; none were reported positive for P. vivax. Resting boxes proved effective, increasing the proportional catch of Anopheles quadrimaculatus to An. crucians. Evolving conditions required a flexible and expanded collection regime: as case numbers increased, growing evidence of un-housed persons in the area added collection sites. Significantly, this investigation witnessed, first-hand, conditions that reinforce messaging from health agencies regarding the persistent potential for autochthonous malaria to occur in the continental US. Our experience may inform other mosquito control operations in regions with similar risk factors as to how they might respond to an active, locally acquired malaria outbreak. If testing of specimens for malaria is requested, augmented trapping methods for Anopheles should be considered.