August 17, 2022 | Volume 2 | Issue 11 | As of Week 32
Welcome to the Florida Disease Activity Update from the desk of Dr. Jonathan Day.
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.
A QUESTION FROM OUR READERS

Q. Sarah from Vero Beach, FL asks: “What is the significance of the male mosquito’s plumose antennae?”

A*. Another great question from Sarah. It is easy to separate male and female mosquitoes by the size and shape of their antennae as shown below in the beautiful photographs by Larry Reeves from the UF/FMEL. Male mosquitoes have full plumose antennae while females have long, thin, simple antennae. The same is true for many moth species.

The purpose of the plumose antennae in males is primarily sensory. Male moths, especially giant silk moths (family Saturniidae), locate females by following pheromones that are sensed through the antennae. In some giant silk moth species, males can detect and track females that are located miles away.

Male mosquitoes locate potential mates by using visual, olfactory, and auditory cues. The olfactory and auditory cues are received through their antennae. I suspect that the male antennae are plumose because they house so many receptors designed to help the male mosquito orient in its world.
Figure 1. Adult male and female mosquitoes differ morphologically, male mosquitoes have plumose antennae and long palps. Female mosquitoes have simple antennae and short palps.
THE CURRENT OUTLOOK FOR ARBOVIRAL TRANSMISSION IN FLORIDA DURING 2022

The transmission of locally-acquired dengue in Miami-Dade County and the introduction of DENV into South Florida by infected travelers continues to be the primary vector-borne disease problem in Florida (please see below).
 
Low-level EEEV transmission continued to be reported in Florida during week 32. Four new EEEV antibody-positive sentinel chickens were reported in Leon (new County), Nassau (new County), Orange and Walton Counties, bringing the total number of positive sentinel chickens in Florida to 47, which remains well below the 18-year average (2004-2021) of 133 positive sentinel chickens per year. It remains unlikely that we will see a surge in EEEV transmission in the coming months, although the risk of EEEV transmission in Florida is never zero.
 
A single SLEV antibody-positive sentinel chicken was reported this week in Sarasota County, bringing the total of positive chickens in Florida to two. Fall migration will begin in two weeks and with it will come the possibility of increased SLEV introductions and amplification. It is unlikely, however, that SLEV will pose a significant risk to human health in Florida during the remainder of 2022.
 
Transmission of WNV continues to increase in Florida. Seven new WNV antibody-positive sentinel chickens were reported this week in Bay (2), Charlotte, Leon, and Pinellas (3) Counties, bringing the Florida total to 37 positive sentinels spread evenly throughout the state with the notable exception of the central and east coast of the peninsula (Figure 2). Currently, there is no clear WNV transmission focus within the state and it remains unclear as to whether there is a significant risk of human or equine WNV transmission.
Figure 2. WNV antibody-positive sentinel chickens reported in Florida during 2022.
There were 35 new travel-related dengue introductions into Florida this week, 25 of which were in Miami-Dade County (Figure 3). A total of 172 travel-related DENV introductions have been reported in Florida thus far in 2022. Of these, 150 (87%) have originated in Cuba and all four dengue serotypes have been introduced into Florida from Cuba this year, a fact that may play into the severity of human infections reported in Florida during the coming months.

Very little information about the current dengue situation in Cuba is available. However, a recent PAHO summary indicates that there have been 450 locally-acquired cases reported in Cuba. The second page of the Florida Department of Health Arbovirus Surveillance data set probably provides the best information available regarding the movement of DENV out of Cuba and into Florida.
Figure 3. Travel-related dengue introductions in Florida during 2022. Counties colored blue indicate DENV introductions in 2022. Counties colored red indicate the total number of DENV introductions in 2022 and DENV introductions during Week 32.
Between 2009 and 2022 there were 221 locally-acquired dengue cases reported in nine Florida Counties. Most of these were reported in the Florida Keys (Monroe County). However, it is evident from Figure 4 that the entire southern half of the Florida Peninsula is at risk of locally-acquired dengue transmission.
Figure 4. The distribution of locally-acquired human dengue cases in Florida: 2009-2022.
Year to Date Summary of Mosquito-Borne Disease Transmission

As of Week 32, 2022, the following mosquito-borne disease transmission events and pathogen introductions have been reported in Florida:
Table 1. Summary of mosquito-borne disease transmission and introductions in Florida as of August 13, 2022 
The number of travel-related dengue cases in Florida has increased steadily during the past five weeks with an average of 26 new introductions each week for a total of 172 introductions in 2022. 
 
The 12-year average (2010-2021) of travel-related dengue introductions into Florida is 105 per year. The 12-year average of locally-acquired dengue cases in Florida is 16 per year. The steady increase in travel-related dengue introductions into South Florida along with the three reported locally-acquired dengue cases in Miami-Dade County suggests the possibility of a significant outbreak of dengue in South Florida during the coming weeks. Historically, most of the locally-acquired dengue cases reported in Florida have had onset in August and September, so the worst period of locally-acquired dengue transmission is still in front of us.
OPERATIONAL STRATEGIES TO CONSIDER
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.
 
Specific operational strategies will be discussed during the 2022 arboviral transmission season depending on where and when vector-borne disease transmission becomes obvious in Florida.
 
There is currently a low risk of EEEV transmission in Florida.
 
There is currently a very low risk of SLEV transmission in Florida. 
 
There is currently a low to moderate risk of WNV transmission in Florida. 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 a high risk of local dengue transmission in South Florida (Figures 3 and 4). The three locally-acquired dengue cases reported in Miami-Dade County and the continued influx of travel-related dengue cases into South Florida (26 new cases per week) increases the risk of a significant local dengue outbreak. As of now, Miami-Dade County is the most likely focus for such an 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.  
ABOUT DR. JONATHAN DAY
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.

*The reader question this week was answered with the assistance of Dr. Lawrence Reeves at the Florida Medical Entomology Laboratory in Vero Beach.
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