FKMCD hoping to turn the tide in the first major outbreak of dengue since 2010
As the world remains embattled with COVID-19 and the unprecedented level of resources being used to defend against it, a more familiar struggle is being waged by mosquito abatement professionals in the Florida Keys. As if Coronavirus weren’t enough to plague 2020, a dengue epidemic has erupted, the first major outbreak of local transmission in the Keys since 2010.
Through late August, a total of 54 locally-acquired dengue cases had been recorded in Florida in 2020, 53 of those occurring in Monroe County. The first was confirmed just before the pandemic forced lockdowns. Since then, it’s been what Florida Keys Mosquito Control District (FKMCD) Director Andrea Leal is calling a “perfect storm.”
“We were notified of a suspected case in Key Largo in early March and we thought it was probably a one-off,” Leal says. “We responded to the area and did larviciding, adulticiding, door-to-door treatments, etc. That got us all the way until COVID hit. We thought we were in the clear but unfortunately that wasn’t the case.”
Managing the direct effects of COVID-19 have been a daily battle since then, but it was indirect effects that likely fueled the dengue storm. Not only were resources in Florida and all across the country being reallocated to combat COVID, changes associated with quarantining are assumed to have played a complementary role. The onset of COVID meant that people weren’t reporting illness as they would in a typical year.
“Thinking back on it, I’m sure COVID had a lot to do with it because at the very beginning, people were asked not to go into the hospital or go into the doctor unless they absolutely needed to,” says Leal. “So we potentially had some ongoing transmission that wasn’t recognized because everyone was staying home rather than going in to get checked out if they had mild symptoms.”
That all changed in June. After one additional case of locally-acquired dengue was reported in Miami-Dade County in mid-May, additional cases in Key Largo began surfacing almost immediately. Two new cases in the Upper Keys were cited in the June 14-20 Florida Arbovirus Surveillance report, followed by eight more cases the following week. That meant by June 27, 11 confirmed, locally-acquired cases had been detected in a county that had only seen three cases in the previous nine years, none between 2011 and 2017.
FKMCD’s response was immediate. While Leal and her team started to implement Aedes aegypti program enhancements in the Upper Keys, she says the confirmations prompted the Florida Department of Health to start canvassing the affected area.
“The Department of Health is an important partner for us,” Leal says. “In these kinds of circumstances, they will go directly into these areas and go door to door to find out if anybody at those residences is either having symptoms or had symptoms in the past. They went to every residence in the affected neighborhood. When someone reports symptoms, the Health Department directs them to be tested. In the course of their investigation, it turns out that not only did some new cases show up, there were a number of people that reported having dengue symptoms during that March to June time frame.”
Although the number of locally-acquired cases in Monroe County has since climbed above 50, there are distinct positives to report. First, is that the outbreak was localized. Leal says that the neighborhood that spawned most of the cases consists of only about five streets. Of the transmission areas, she says there are three that are identifiable with clusters. All three are in the Key Largo area.
“We’re not seeing anything outside of that island,” Leal says.
The FKMCD team suspects that while COVID played an indirect role in promoting the outbreak, the public’s lack of movement also helped keep it confined.
“The questionnaires from the Health Department told us that a lot of people were spending more time outside because essentially, they had nothing else to do,” says Leal. Since they couldn’t go out and about like normal, they were maybe walking their dogs multiple times a day – or stopping by and talking to their neighbors from the street. That sort of thing. That means that more of the neighborhood was exposed than normal. But at the same time, they weren’t going too far from home. That helped keep it isolated.”
Operationally, FKMCD had to put several measures in place, quickly. Leal indicates that under normal conditions, the district has six inspectors that cover all of the Upper Keys from Key Largo down through Islamorada. To address the outbreak, the district brought 15 other employees from the Lower and Middle Keys to assist in the area, going door to door three to four times a week, doing inspections and leaving information behind about source reduction. They also began WALS™ aerial applications of VectoBac® WDG – atypical for the Upper Keys.
To help with the WALS effort, Valent BioSciences (VBC) Technical Development Specialist Leanne Lake traveled with technical sales specialists Candace Royals (VBC) and Larry Heller (ADAPCO) down to Key Largo on June 29 to help the FKMCD team characterize VectoBac WDG WALS droplets for a new helicopter. Last April, Lake, Leal, and several other leading experts trained mosquito abatement professionals from across the US during a virtual summit on the WALS application strategy.
Lake says that historically, WALS aerial applications in the Keys had been limited to Key West, but the dengue outbreak prompted a rapid change to the program. The first-ever WALS aerial applications were conducted by Leal – then FKMCD Operations Manager – in Key West in 2010, and played a major role in overcoming the region’s last dengue epidemic.
After proper calibration and characterization, Key Largo received its first WALS aerial applications of VectoBac WDG in early July.
“We typically only do aerial (Vectobac) WDG treatments in Key West because that was where our main area of concern has been,” Leal says. “However, we’ve now added about 2400 acres of (VectoBac) WDG treatments in Key Largo as well.
On the Front Lines
Leal says that despite all the best epidemiological efforts, they’ll probably never know exactly how the dengue virus was introduced to Key Largo. FKMCD had traps placed across the Keys in all of the areas known for Aedes aegypti prior to the outbreak, but none in the newly affected neighborhoods. They immediately added 10 new traps across all of the suspect areas of Key Largo, monitoring the Ae. aegypti numbers and then working with the Department of Health to have all of those mosquito pools PCR tested at the CDC Dengue Branch in Puerto Rico. Testing was moved to the branch early on in the pandemic when capacity at mainland labs was consumed by COVID testing.
While the team may never be able to determine exactly when, by whom, or how the virus was introduced, they do know that 2019 was a particularly challenging year in Florida for imported dengue cases –particularly in Miami-Dade. That dynamic would continue into the early weeks of 2020. This high incidence rate may have yet been another contributing factor in the outbreak. In 2019, the state experienced 359 imported Dengue cases, 239 emanating from Cuba. Of the 359 cases, 226 were recorded in Miami-Dade, just a short drive from Key Largo.
Communications, as always, plays a vital role in quelling any outbreak. FKMCD Public Information Officer Chad Huff says the district immediately adapted and activated its disease response plan, which includes a multi-pronged communications effort to inform and engage the public in response efforts. Central to communications is the “Dump Dengue” tagline the team utilized .
“The first prong in our efforts is using our social media accounts to hammer home the Dump Dengue phrase,” Huff says. “It’s a really simple message that we include with essentially anything we place on social media now. It helps people understand that by dumping standing water, they can help reduce dengue risk. We have to assume that person may only have heard there is dengue in the Keys, but they haven’t heard where. So whether it is Key Largo, or Key West, or Grassy Key, long term it’s beneficial to keep everybody informed and involved in the solution.
“The second prong has been a very aggressive radio Dump Dengue campaign,” says Huff. “We already had spots scheduled on five or six Keys radio stations for the rainy season, so we adapted those to the Dump Dengue campaign and bought some additional time specifically in Key Largo.”
Huff says that the third component in the plan involved engaging and communicating with the homeowners association in the hardest hit Key Largo neighborhood. Huff created a newsletter for residents that includes information on both dengue symptoms and prevention. The district continues to stay in communication with the neighborhood to keep them apprised on progress and continue to ask if the neighborhood is aware of any unmet mosquito control needs.
“We try to keep it high level,” Huff says. “We don’t share specific trap results but we’re communicating that our data shows that the traps are trending with fewer and fewer Aedes aegypti. It’s important that they know that what we’re doing – together – is working. But that we need to keep it up.”
Huff says the president of the HOA is also sharing Keys’ posts and press releases on the Associations Facebook page.
According to Huff, collateral is another important element of the program. FKMCD inspectors are equipped with door hangers as a leave behind that includes information on the nature of mosquito breeding sites. Huff modified the design so that the dengue information pops, calling attention to its symptoms and prevention tactics. Inspectors are also outfitted with CDC flyers on source reduction.
To facilitate changes in their application strategy, FKMCD worked with the local board of education in Key Largo to secure a general purpose field at an elementary-middle school. This would serve as a base for the new WALS applications. In the past, Leal says, there hadn’t been a suitable base on Key Largo from which to conduct aerial (WALS) larviciding.
“All of Florida’s schools remain online for now,” Leal says, “so with students still at home, this particular location became available to us. It was perfect for what we needed. It’s a wide-open space in a gated off area, so it’s easily accessed by our crews but we don’t have people wandering in.”
Leal says the location is right in the middle of the treatment areas, which saves time and taxpayers’ money. The close proximity of the school to the affected neighborhoods eliminated the ferrying time necessary when applicators initially had to return 10 miles to the south to reload. She says applications are now taking place first thing in the morning, twice a week.
There is no doubt that the community and FKMCD team’s Integrated Vector Management (IVM) efforts are having a positive effect. While the public has seen dengue numbers continue to increase (August Arbovirus Surveillance Reports list 26 new cases), the vast majority of those are actually retrospective cases – added by the Health Department once antibody testing from early suspect cases were confirmed.
Dr. Banu Kesavaraju, Global Technical Manager at Valent BioSciences has been working with FKMCD and other Florida districts on WALS applications since 2015. He says the precipitous drop in acute dengue cases is what you’d expect to see from an IVM program that includes WALS and other important IVM measures.
“The published WALS data – in particular from the Keys – supports these kinds of results,” Kesavaraju says. “WALS helps mosquito control districts deliver biological larvicides into hard-to-reach, cryptic habitats were Aedes aegypti breed. We know that when WALS applications began in Key Largo in early July, there were already infected adult mosquitos present. We also know that with proper environmental conditions, infected adults can persist for another 20-30 days, if not longer. Now that WALS applications have been ongoing for two months, we can see a corresponding decline in acute cases of dengue. While it’s certainly not the only reason, we know that VectoBac WDG and WALS applications as part of an IVM program have been major contributors to the virtual absence of dengue in the Keys for the last decade.”
Total Locally-Acquired Dengue Cases:
Monroe County Florida, 2020
|Dengue Cases by Month of Onset|
Data through 8/27/20
Source: Florida Department of Health