Facing a new enemy: Zika. The Miami experience

In 2016, the Zika virus caught U.S. mosquito control programs off guard. Until then, the Aedes aegypti species that vectors Zika was considered a nuisance mosquito. Suddenly, it became a major disease transmission threat that could not be effectively controlled by traditional measures. There were two reasons: – Aedes aegypti bites during the day. Controlling it with traditional adulticides would require daytime versus nighttime applications, which is unacceptable to the public. small and cryptic, impossible to treat individually. – Aedes aegypti breeds in very places With the peak tourism season about to begin, officials in Miami-Dade County, Florida, needed to define an immediate control program to get it underway. Realizing the scope of their challenge, the Miami-Dade Mosquito Control District asked Clarke for help. A ROUGH START Faced with the need to act urgently, the Miami-Dade Mosquito Control District initially followed the CDC protocol for emergency disease control: Nighttime aerial applications to suppress mosquito populations. This approach was only moderately successful given the diurnal activity of the species. In addition, it was met with significant rejection from the public. Since the target was cryptic breeding species, the challenge was how to deliver wide-area larval control treatments to millions of small breeding sites. From the tops of palm trees and succulents in the ground, to footprints on a construction site, breeding sources were literally everywhere. A daytime aerial application of larvicides was performed in the hope that the tiny atomized droplets would float to the numerous small breeding sites. However, this was also rejected by the public. Clarke's team then asked how to make a ground application that would release ultra-low volume droplets 150 – 180 feet into the air so they could float in and around buildings and garden areas and in cryptic breeding sites. RAPID CREATIVITY The answer was discovered using an air sprayer called the Buffalo Turbine, an applicator that had been used in agricultural tree, nut and vine crops. Within two weeks, Clarke obtained a sprayer and retrofitted it with a nozzle system capable of producing effective droplets. And with the force of the air column driven by a turbine, it was possible to distribute the droplets over a wide area. A NEW CONTROL APPROACH Armed with this new application method, Clarke and Miami-Dade Mosquito Control created a two-pronged strategy to combat and contain the fast-spreading virus. 1. Carry out wide-area larvicidal treatments at night with the Buffalo Turbine while citizens sleep to suppress global populations of Aedes aegypti. 2. Conduct door-to-door inspections and treatment within a radius of known Zika cases to suppress transmission. Aedes aegypti has a very short flight range, on average just two city blocks, making this door-to-door surgical approach efficient and effective. This approach was called SITE Guard – Surveillance, Inspection, Treatment and Education. Two-person teams went door-to-door, educating residents about Zika-transmitting species and asking them to inspect property in more than 41% of residences, and in 45% only in the front yard. Only 13% of the residences in the target area could not be visited. If hatchlings or adults were found, treatment was carried out. Treatments against larvae were carried out with granule and tablet formulations of Natular (Spiniosad). If adult mosquitoes were found, barrier applications were made to the foliage surrounding the property. This approach allowed teams to conduct comprehensive inspections, making the overall SITE Guard program a successful element of the mosquito control program. Thanks to this, within two years the problem was controlled, setting a precedent and establishing the necessary procedures to stop the spread of Zika and keep mosquito populations at a low level.