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. During the past 12 years (2010-2021) an average of 34 SLEV antibody-positive sentinel chickens have been reported in Florida each year. The most recent heavy SLE transmission year was 2014 when there were 106 positive sentinel chickens and two human SLE cases (both in Duval County) (Figure 1). Recently, most sentinel chickens have seroconverted to SLEV in the spring and fall and there has been little indication of focal amplification and transmission of the virus. For example, in 2017 there were 11 positive sentinel chickens reported in seven widely dispersed Florida counties (Figure 2). It appears that SLEV is periodically reintroduced into Florida and has had difficulty establishing significant transmission foci. Migratory birds would be a great source of SLEV reintroductions into Florida and would also serve as amplification hosts in the spring and fall. It will be interesting to monitor the transmission of SLEV in Florida and determine whether significant transmission foci can be reestablished in the state. 

Two new EEEV antibody sentinel chickens were reported in Leon and Pasco Counties bringing the number of EEEV antibody-positive sentinel chickens in Florida to 57, well below the 18-year average (2004-2021) of 133 positive sentinel chickens per year. Two EEEV-positive equines were reported in Hillsborough County, both were likely infected in late August. This indicates that there is still a risk of EEEV transmission in Florida even though the number of positive sentinel chickens is well below the 18-year average and we have to remain aware that the risk of EEEV transmission in Florida is never zero.

A single SLEV antibody-positive sentinel chicken was reported in Palm Beach County, bringing the total number of positive sentinel chickens in Florida to four. 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.

Six 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. Four 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.

Fifty-eight travel-related dengue cases were reported in Florida last week, 34 of which were in Miami-Dade County (Figure 4). A total of 371 travel-related DENV cases have been reported in Florida thus far in 2022. Of these, 335 (90%) originated in Cuba. 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.

 

Fourteen locally-acquired dengue infections have been reported in South Florida in 2022. Thirteen are in Miami-Dade County and one is in Collier County. This indicates that there are now multiple dengue transmission foci in South Florida. The virus has likely entered Florida multiple times so far in 2022. 

Figure 4. Travel-related dengue cases in Florida during 2022. Counties colored blue indicate dengue cases occurring in 2022. Counties colored red indicate the total number of dengue cases in 2022 and travel-related dengue cases reported during Week 36.

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 to moderate 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 3. 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 (Figure 4). The 14 locally-acquired dengue cases and the continued reports of travel-related dengue in South Florida (50 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. 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 newly emerged 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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