It continues to be Clarke’s privilege to share Dr. Day's weekly analysis of arbovirus disease activity in Florida with mosquito control professionals across the state. Our shared goal with Dr. Day is to provide timely and actionable information that mosquito control programs can use to make operational decisions and protect public health from vector-borne diseases.

An archive of all past newsletter issues remains available on the Clarke website.

Q. Marianne from Vero Beach, FL asks: “I have a lot of daytime biting mosquitos in my yard. What can I do to get rid of them and do I need to worry about diseases they might transmit?”

A. There are two mosquito species that may be biting in your yard during the day: Aedes aegypti and Aedes albopictus. Both adults are stunningly beautiful when newly emerged and they are easy to identify (Figure 1).

There are three things you need to do to solve your problem. First, confirm that the mosquitoes biting you are Ae. aegypti and/or Ae. albopictus. Second, locate their larval habitats. Third, destroy the larval habitats. I am 90% confident that your problem is one, or both, of the mosquitoes in Figure 1. Larval habitats are most likely artificial containers (toys, gutters, cans, jars, bird baths, plant pot overflow dishes, or plastic wrap) or natural containers (tree holes and/or water-holding plants like bromeliads). Find the larval habitats and drain them. Tree holes can be filled with sand. Bromeliads or similar plants are a problem and you may have to replace them with a plant, like a cactus, that does not hold water.

You do need to worry about potential disease transmission by both of these mosquito species. If you, or one of your neighbors, travels to a destination where dengue, Chikungunya, Zika, or yellow fever viruses are actively being transmitted, the virus may be introduced into your neighborhood after the return of the traveler. This occurs when the traveler is bitten by an infected mosquito at their port of call. For example, dengue in Miami, Zika in Puerto Rico, or yellow fever in Brazil. If the traveler returns home with an active infection, it is possible that your mosquitoes can become infected by feeding on that individual. When this happens, an active focus of disease transmission may be established in your neighborhood. While this is rare, it does happen.

For example, in August and September of 2013, a focus of dengue transmission (12 confirmed cases) was reported in Martin County, Florida. The outbreak was traced to a home surrounded by bromeliads that supported a very large Aedes albopictus population.

There were no new reports of EEEV transmission in Florida last week. The number of EEEV antibody-positive sentinel chickens in Florida remains at 55, well below the 18-year average (2004-2021) of 133 positive sentinel chickens per year. It is unlikely that there will be a dramatic increase in the transmission of EEEV in the coming months, although the risk of EEEV transmission in Florida is never zero.

A single SLEV antibody-positive sentinel chicken was reported in Seminole County last week, bringing the total number of positive sentinel chickens in Florida to three. There is no indication of any active SLEV transmission foci in Florida. At this time, SLEV does not pose a risk to human health in Florida.

Five WNV-positive mosquito pools have been reported in Florida so far in 2022. Two were collected in Sarasota County in late July and both were pools of Culex quinquefasciatus. Three were collected in Lee County in late July and early August. All were pools of Cx. nigripalpus. The isolation of WNV from these two mosquito species suggests that both urban (Cx. quinquefasciatus) and rural (Cx. nigripalpus) WNV transmission foci are currently active in Southwest Florida.

Figure 3. Travel-related dengue introductions in Florida during 2022. Counties colored blue indicate DENV introductions during 2022. Counties colored red indicate the total number of DENV introductions in 2022 and DENV introductions during Week 35.

Vector and arboviral surveillance remain some of the most important tools that vector control agencies currently have at their disposal. Arboviral transmission indices (sentinel chickens, positive equines, positive exotics such as emus), positive humans, and positive mosquito pools provide indicators of local virus transmission, although sometimes not in a timely manner. Monitoring mosquito populations and their age structure gives additional information about potential transmission risks. Supplemental vector control efforts in and around sites where virus transmission is known or suspected of recently occurring provide another mechanism to mitigate viral transmission.

There is currently a low risk of EEEV transmission in Florida.

There is currently an extremely low risk of SLEV transmission in Florida. 

There is currently a moderate to high risk of WNV transmission in Florida in the two transmission foci shown in Figure 2. Arboviral surveillance and reporting during the upcoming weeks will help to determine the current situation relative to the transmission of EEE, SLE, and WN viruses throughout the state.

There is currently an extremely high risk of local dengue transmission in South Florida (Figures 3 and 4). The 14 locally-acquired dengue cases and the continued introduction of travel-related dengue into South Florida (44 new cases per week) increase the risk of establishing additional dengue transmission foci and increase the risk of a significant outbreak of locally-acquired dengue infections. As of now, all of South Florida is at risk for a dengue outbreak. Increased Aedes aegypti control in areas surrounding locally-acquired and travel-related dengue cases will help to reduce the number of infected and emerging vector mosquitoes.

Source reduction, the emptying, and where possible the destruction, of all water-holding containers remains the most productive control method against the likely dengue vector, Aedes aegypti. Cryptic Ae. aegypti breeding habitats remain a huge problem in places where this species is abundant. The location of these cryptic habitats remains one of the primary challenges for vector control agencies dealing with dengue outbreaks. 

Jonathan Day, Professor Emeritus of Medical Entomology from the University of Florida, is a national expert on mosquitoes and other blood-feeding arthropods that transmit diseases to humans, domestic animals, and wildlife. In collaboration with other researchers, Dr. Day has developed an effective system for monitoring and predicting epidemics of mosquito-borne diseases.

Acknowledgments: This analysis would not be possible without the tireless efforts of multiple agencies across Florida. At least 27 Florida agencies collect serum samples from sentinel chickens each week and mail them to the Florida Department of Health Tampa Branch Laboratory for analysis, compilation and reporting. Data are summarized by researchers at the Florida Department of Health in Tallahassee and reported weekly as the Florida Arbovirus Surveillance Report.

Contributors to this summary and full report include: Andrea Morrison, PhD, MSPH, Rebecca Zimler, PhD, MPH, and Danielle Stanek, DVM, Florida Department of Health, Bureau of Epidemiology; Lea Heberlein-Larson, DrPH; Alexis LaCrue, PhD, MS; Maribel Castaneda, and Valerie Mock, BS, Florida Department of Health Bureau of Public Health Laboratories, and Carina Blackmore, DVM, PhD, FDOH Division of Disease Control and Health Protection. And, Dr. Rachel Lacey, Florida Department of Agriculture and Consumer Services, Animal Disease Diagnostic Laboratory in Kissimmee, FL.

Daily updates of the Keetch-Byram Drought Index (KBDI) are produced by the Florida Department of Agriculture and Consumer Services, Forest Service.

All of the graphics used in issues of this Newsletter are designed and developed by Gregory Ross.

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