At this time last year, public awareness in North America started to turn, for the first time, toward a little-known disease called Zika. First identified in Uganda in 1947, Zika virus branched into African and Asian strains that were not known to cause meaningful infections in humans. That changed when a Zika epidemic broke out in Micronesia in 2007. In 2013, the first known link between Zika and neurological disorders was reported during an outbreak in French Polynesia, suggesting the virus had mutated to a form much more aggressive in humans.
What is now characterized as the Brazilian strain of Zika arrived in South America sometime in 2013. Since then, more than 128,000 confirmed cases of Zika have been recorded in Brazil. In October 2015, Brazilian researchers reported seeing unusually high incidence of birth defects, mainly microcephaly, among infants born to mothers who had contracted Zika during pregnancy. CDC confirmed the link between Zika and microcephaly the following April. A total of 2,200 Brazilian infants are known to have been affected.
In early 2016, studies on Zika risk began to emerge. In March, Monoghan et. al published a study outlining the risk of Zika occurrence in the contiguous United States (see Public Health Landscape, Volume 26).1 Months before any locally-transmitted Zika cases would be confirmed in the U.S., the Monoghan study identified Miami, FL as the baseline for optimal Zika environmental conditions and identified counties in South Texas, including the area around Brownsville, as likely Zika hotbeds. By the end of the calendar year, those would become the first two locations where locally-acquired Zika would be confirmed in the U.S.
The first cases were confirmed in Miami-Dade County in late July. A total of 35 cases were confirmed by the end of August, a number that would swell to more than 200. Still, the outbreak was quelled and Florida health officials lifted the Zika warning from the last of four local zones on December 9th. Locally- acquired transmission was confirmed in Brownsville, TX on November 28.
Today, in the wake of this first bout with Zika, public health officials are fine-tuning response plans and adapting programs for control of Aedes aegypti (L.), the primary vector of Zika. By all accounts, Florida’s response was swift, highly effective, and instructive.
In a January 2017 State of the County speech, Mayor Carlos Gimenez proudly noted that Miami-Dade had been the first and only community in the world to break the cycle of local transmission of Zika. It’s a victory that had its roots in container mosquito work performed by the Florida Keys Mosquito Control District (FKMCD) years earlier.
Like Zika, dengue and chikungunya are transmitted by day-biting, container breeding Aedes mosquitoes. Prone to breed in urban and hard-to-reach, small water habitats, Ae aegypti ecology requires a different approach than Culex species, which vector West Nile Virus and other important diseases. In 2010, when FKMCD experienced the district’s first locally-acquired dengue outbreak in nearly 75 years, the District took action by launching a strategic communications program to educate residents on source reduction as well as a strengthened Integrated Vector Management (IVM) approach targeting container mosquitoes. Among its operational adaptations, FKMCD conducted the first-ever wide-area, aerial applications of water dispersible Bacillus thuringiensis subsp. israelensis Strain AM65-52 (Bti) larvicide to address Ae aegypti habitat challenges.
FKMCD demonstrated that aerial applications of VectoBac® WDG allowed FKMCD to deliver a targeted biorational product into cryptic habitats, complementing the other elements of the District’s updated program. Once the changes were implemented, locally-acquired dengue cases dropped to zero the next year and would remain so until a single case of dengue was diagnosed in Key West last summer.
The success of the Keys program garnered quite a bit of attention from other abatement districts in Florida and beyond, interest that accelerated once Zika started to emerge. Several districts scheduled training and gained experience in aerial and ground-based Bti applications in the early part of 2016.
Miami-Dade County Mosquito Control was among the first districts to get advanced training in aerial and ground-based applications of VectoBac® WDG (Valent BioSciences Corporation (VBC). VBC provided the County with a technical training workshop regarding aerial and ground applications of VectoBac in May. When the first Zika cases were detected there in July, the district responded by combining aerial applications of VectoBac® WDG with Dibrom® (naled, AMVAC) in the Wynwood District on the advice of the Centers for Disease Control (CDC). Ground-based WDG applications were also conducted in Miami Beach and Little River, just north of Wynwood.
The result was eye-opening. On August 15, the Miami Herald reported that the integrated approach of larvicide plus adulticide was more effective than application of a stand-alone product.
“In a two-square-mile zone that covers the Wynwood arts district at the center of the outbreak, the population of mosquitoes has declined under an aerial spraying program that uses two different pesticides — one that takes out adults, the other that kills mosquito eggs and larvae. But in the remaining 80 percent of the 10-mile-square zone targeted for Zika eradication where naled alone is sprayed to kill adults, the Aedes aegypti has held its ground.”2
In the article, Dr. Janet McCallister, the CDC entomologist advising the district on applications, acknowledged what had already been seen in the Keys years earlier.
“In areas without the larvicide, the adult populations [of Ae aegypti] are rebounding much quicker and much higher than in the area [treated] with both,” McAllister said.
As part of its response to the Zika outbreak, the Valent BioSciences Public Health Team has created a series of instructional videos to help mosquito abatement personnel learn about using VectoBac®WDG to effectively treat for mosquitoes using backpack and aerial applications. The videos include backpack configuration and operation, calibration, site surveying, spray mixture calculation and preparation, and backpack loading. Also included are videos exploring the differences between rotary wing and fixed wing aircraft application and the benefits to using each. To access these videos, visit the Zika Resources portal at
Meanwhile, surrounding districts were putting their own plans into action. Anh Ton, Highway Bridge Maintenance Director for Broward County, Florida, which oversees Broward’s mosquito control activities, says the district started monitoring Zika migration in South and Central America a few years ago.
“We know that South Florida is a gateway for these kinds of diseases,” Ton says. “Our residents travel back and forth frequently to places that were already experiencing Zika. We had to be prepared.”
Ton’s dedicated mosquito control staff consists of just eight inspectors and one entomologist responsible for 500 square miles and 1.9 million inhabitants. Ton knew that heading into 2016, the proximity of Zika required immediate development of a response plan that included cross-training. Some of the highway crew got applicators licenses and others were trained to take calls in the event of an outbreak. The team also collaborated in tabletop exercises with the County Health Department and local municipalities to talk through how things would work when and if Zika appeared. All told, 31 cities participated.
As part of the preparation, Ton and other staff members visited the Keys to see how they loaded and what to look for.
“What really struck me was that we had to target the larvae to be more effective,” Ton says. “All day long we walked around and I saw how well their staff was interacting with people. I thought about how we needed a product that took into account homes and pets and other critters. We needed to be able to explain to the public what’s going on and to gain their acceptance of our efforts.”
Ultimately, the team determined that VectoBac® WDG met those criteria. As in Miami-Dade, VBC provided a technical training workshop in May surrounding aerial and ground applications of WDG. When the response plan kicked in a few months later, rotor wing aerial applications of the larvicide began in Broward in September. Working with an experienced applicator, VBC oversaw mixing/loading, and provided cup placement/bioassay for efficacy assessment.
Once again, the data told the story. Jar tests showed high coverage of VectoBac® WDG ranging from 100% in open areas to 94% under heavy vegetative cover. VectoBac® droplets even reached 69% of fully obstructed jars placed under tables, carports, and porches. Larval mortality 48 hours after application ranged from 97% in open sites to between 86% and 78% in areas with heavy vegetation (see Figure 1).
Jim McNelly moved from the private sector to become Director of Mosquito Control in Volusia County, Florida in 2011. The district has a staff of 21 full-time and nine seasonal workers. McNelly knew the county had a strong salt marsh program, but says there was something else on his mind when he took the position.
“One of my first questions to the team was, ‘What about aegypti?’” McNelly recalls.
Having worked in the industry, McNelly knew what had taken place in the Keys. After using WDG in backpacks with good results for a few years, McNelly decided to trial aerial applications for the first time in 2016 as part of the district’s Zika Response Plan.
“We knew the results they had gotten in the Keys, and we wanted to be able to replicate those results if we needed to,” McNelly says. “We knew a fixed wing aircraft was being used in Miami as part of the Zika response, but we wanted to keep our trial as “apples to apples” to work performed in the Keys – and we currently use two helicopters in our program. With our first application, we had overall mortality rates in the 93-95% range, with 100% in many areas.”
McNelly says that the Keys approach “will become part of our disease response routine.” The robust program and strong surveillance systems in the district allow him to sleep easier at night.
“First and foremost, you have to have a response plan in place,” McNelly says. “Then it’s easy to make the decision to go to that next level when you have to be more aggressive.”
In Pinellas County, Mosquito Control Director Brian Lawton began developing a response plan with Assistant Operations Manager Glen-Paul Edson and Lead Spray Technician Leanne Lake. As part of their strategy, the team built a taskforce in collaboration with State and local Department of Health. It included provisions for sending a team out, door to door, inspecting properties and handing out pamphlets aimed at source reduction education.
“Having a plan was a top priority for our District,” Lawton says. “Connecting with the public is critical. People are really sitting up taking notice to what we’re talking about now. The local officials, in particular, seem to understand the importance of what we’re doing.”
When Edson decided to set up field trials for Ae aegypti control using Bti, the VBC field support team visited to conduct training. With demand for WDG field support rising, the team used the opportunity to produce training videos in the process, videos that instruct abatement personnel how to mix the WDG and how to calibrate their sprayers (see sidebar on page 2).
Lake adds that the County has another dynamic that’s somewhat unique. The area is home to a large concentration of beekeepers, something spray technicians need to be aware of when insecticide applications are imminent.
“Our approach is to use biologicals whenever we can,” Lake says. “We have to be able to produce the labels for what we’re using and it helps a lot when I can hand them something that’s OMRI certified. You’re always going to have some concerns when you’re applying pesticides but our outreach efforts have helped folks understand that we’re using the most gentle products. Part of that process was initiating proactive communications with our beekeepers to keep them informed. It created a sense of trust and we have a great relationship as a result.”
NEW YORK CITY
No locally-acquired Zika transmissions have been reported in New York City. That doesn’t mean that NYC mosquito-borne disease control officials are standing idly by. Dr. Waheed Bajwa leads NYC’s mosquito control efforts. The district spans five boroughs (Manhattan, Bronx, Brooklyn, Queens and Staten Island) with a population of more than 8.5 million. No less than 51 species of mosquitoes are well established in New York, most of which can be found in all five boroughs.
While in the past the District’s main focus was on Culex species, Bajwa and his team have seen a dramatic rise in Aedes albopictus over the past several years.
“We’ve spent quite a bit of time in the recent past learning to control container breeders and keep risks down,” Bajwa says.
Bajwa and his team have spent five years studying container mosquito ecology. The adaptability of Aedes means that NYC is home to some unique biology. In short, Bajwa says that mosquitoes in NYC don’t necessarily act the same way as mosquitoes do outside the city.
“The habitats here are unique. They are many and they are various,” says Bajwa. “We’ve been studying these species while at the same time building our capacity. We used to have only 14 spray trucks. Now we have 28. This year, for the first time, we began targeting larval habitats with truck-mounted sprayers. Using new technology we’ve been able to greatly increase our covered area with a similar amount of resources.”
In an effort to help the District prepare, VBC field specialists trained about 30 of Bajwa’s ground-based technicians on WDG applications. Bajwa notes it is experience that his team could have gained on their own, over time, but that having a partnership with private industry greatly accelerated the process.
“You anticipate having a few hiccups with any new technology, so it makes a big difference to have support on hand so you can iron things out. We have excellent relationships with VBC and Clarke [Mosquito Control]. We want to learn and we want to implement. We can do it ourselves, surely, but it is always good to have the experts there to help you. There is no substitute for those kinds of partnerships.”
Bajwa reports that while the district has only increased applications by 8% since bolstering its Aedes program, it has increased ground-based larvicide applications by 200% along with another 200% increase in aerial applications.
“We’ve seen the results,” Bajwa says. “Those increases are directly tied to results that we’ve seen. WNV transmission in New York is down six-fold.”
LOS ANGELES COUNTY
Across the country on the West Coast, California vector control officials are engaging in similar acts of preparedness. Truc Dever, General Manager of the Greater Los Angeles County Vector Control District, says the entire state was abuzz watching what was going on in Florida and wondering if California was going to be next in line for Zika. Like her peers in Florida, Dever sees a silver lining in the way Zika has brought people, state and local departments together.
“Albopictus arrived here in 2011, aegypti in 2014,” says Dever. “Since then, districts have been doing all we can to abate Aedes mosquitoes and keep public health risks down. But Zika really upped the ante. All the things that we try to educate the public about, Zika brought to the fore. It lit a fire. We had the attention of the public and local officials and started putting a plan together.”
Central to that process was Kenn Fujioka, District Manager of the San Gabriel Valley Mosquito & Vector Control District, part of LA County. Dever and Fujioka worked with the County Department of Health to help bring core planning personnel together from across local and state agencies including those in public works and agriculture. More than 100 individuals participated in weekly tabletop meetings to develop a response plan that’s soon to be finalized.
“It was a fascinating and rewarding process,” Fujioka says. “There were no egos. No turf issues. Everyone stayed focused on the facts and what we were there to accomplish. We committed to a science-based approach with an eye on operations, funding, communications, and scope. The potential impact is profound. It deserved attention and we provided it. We’re most proud of that.”
“There are other public health agencies out there with differing priorities and methods for accomplishing those priorities. What makes them efficient? What makes us efficient? These were unknowns between us, but they were details that we had to communicate to gain real understanding and choose the best path forward. We needed to find the places where our efficiencies could intersect.”
Volunteer groups play a huge part in the plan. Even though the Greater LA County Vector Control District has 74 full-time staff members devoted to mosquito control, Dever says it’s just not enough for a district of their size. Thousands of people from volunteer groups will be trained to go door to door educating about source reduction in the event of a Zika outbreak.
Is transmission in California inevitable? Dever is thoughtful in her reply.
“At the end of the day we’re a close-knit community. We don’t work in a vacuum,” she says. “Going to the annual AMCA [American Mosquito Control Association] meeting has been vital. We’re in constant communication with districts in Florida and elsewhere. We see what happened in Miami-Dade and how they were able to break transmission with an IVM model. We’ve refined our program based on that knowledge while taking into account our own unique dynamics. So for now, we’ll hope for the best but plan for the worst.”
1 “On the Seasonal Occurrence and Abundance of the Zika Virus Vector Mosquito Aedes Aegypti in the Contiguous United States.” PLOS Currents Outbreaks. 2016 Mar 16 . Edition 1; Monaghan, A.J.
2 Staletovich, J. (2016, August 15) Air attack against Zika hit and miss in Miami, CDC reports. Miami Herald. Retrieved from http://www.miamiherald.com.
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