October 26, 2022 | Volume 2 | Issue 20 | As of Week 42 |
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Welcome to the Florida Disease Activity Update from the desk of Dr. Jonathan Day. |
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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.
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A QUESTION FROM OUR READERS
Q. Beckham from Vero Beach, FL asks: “What accounts for the large number of locally-acquired dengue cases in Florida this year?”
A. Unlike West Nile virus, the dengue virus is not endemic in Florida and needs to be reintroduced each transmission season for there to be locally-acquired dengue cases. Dengue virus can be reintroduced by infected mosquitoes or by infected travelers. Table 1 summarizes the relationship between travel-related and locally-acquired human dengue cases in Florida from 2010 to 2021 when an annual average of 105 travel-related and 16 locally-acquired dengue cases was reported. It is clear that 2022 has been a busy year for dengue transmission in Florida with 590 travel-related and 35 locally-acquired dengue cases as of 10/22/22.
The vast majority (92%) of travel-related dengue cases in 2022 have originated in Cuba and more than half of those have been the DENV 3 serotype. It is evident from Table 1 that years like 2011 and 2020 with low travel-related numbers can produce locally-acquired dengue cases. So far in 2022, at least ten locally-acquired dengue cases have been associated with travel-related cases living in the same household and one locally-acquired case has been associated with a previous dengue case at the same work location (Figure 1).
One thing is clear, there are competent vector species of DENV (Aedes aegypti and/or Ae. albopictus) associated with many of the travel-related dengue cases in Florida. These mosquitoes bite infected travelers and initiate outbreaks of locally-acquired dengue in households or workplaces frequented by the travel-related cases. Clearly, timely inspection and vector control efforts are needed for all travel-related dengue cases in Florida.
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Table 1. Summary of travel-related and locally-acquired human dengue cases in Florida from 2010 through 2022 (as of 10/22/22). (Source: FDOH Arbovirus Surveillance Reports, 2010-2022) |
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Figure 1. The distribution of locally-acquired dengue cases in Florida as of 10/22/22. Counties colored red reported locally-acquired dengue cases associated with travel-related cases in the same household. |
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THE CURRENT OUTLOOK FOR ARBOVIRAL TRANSMISSION IN FLORIDA DURING 2022
Arboviral transmission and the reports of travel-related dengue and malaria cases in Florida are beginning to slow down. Some arboviral surveillance programs and the FDOH Bureau of Public Health Laboratories in Tampa have rebounded. It was certainly nice to see sentinel chicken submissions from Lee County this week after being hit so hard by Hurricane Ian.
Nine new WNV antibody-positive sentinel chickens were reported in Florida last week (five from Lee County). Two new EEEV antibody-positive sentinel chickens were reported in Alachua and Walton Counties. Five new locally-acquired dengue cases were reported in Broward (2 new cases), Miami-Dade (2), and Volusia (1) Counties, bringing the total number of locally-acquired dengue cases in Florida to 35 (see this week’s Question From Our Readers). Seventeen new travel-related dengue cases were reported in South Florida last week. There were no reports of HJV or SLEV transmission in Florida last week. The risk of transmission for EEEV, HJV, and SLEV is currently low in Florida, but it is important to remember that arboviral transmission risk in Florida is never zero. The risk of WNV transmission in some parts of Florida, especially the Panhandle is currently moderate to high.
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Figure 2. Travel-related dengue cases in Florida during 2022. Counties colored blue indicate travel-related dengue cases reported during 2022. Counties colored red indicate travel-related dengue cases reported during the last week (Week 42). Numbers indicated the total number of travel-related dengue cases reported in each county during 2022. |
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Year to Date Summary of Mosquito-Borne Disease Transmission
As of Week 42, 2022, the following mosquito-borne disease transmission events and pathogen introductions have been reported in Florida:
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Table 2. Summary of mosquito-borne disease transmission and travel-related cases in Florida as of October 22, 2022 |
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We are approaching the end of the 2022 arboviral transmission season in Florida. Sentinel chicken seroconversions and reports of travel-related cases (dengue and malaria) are decreasing. Outbreaks of locally-acquired dengue cases continue to be reported and it is evident that there is a risk of local dengue transmission anywhere in Florida where travel-related cases have been reported (Figure 2). |
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OPERATIONAL STRATEGIES TO CONSIDER |
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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 an extremely low risk of SLEV transmission in Florida.
The current risk of WNV transmission remains high in some regions of Florida and low in others. We are rapidly approaching the time of year when the risk of a widespread outbreak of human WN is unlikely.
The relationship between travel-related and locally-acquired dengue cases is important and is summarized in the answer to this week’s question. Most South Florida homes and businesses have an associated population of Aedes aegypti and/or Ae. albopictus. Some of these populations are very evident and some are cryptic. As long as there are travel-related dengue cases in Florida, there will be a risk of locally-acquired cases and the importance of rapid inspection and vector control efforts in every place associated with a travel-related dengue case in Florida cannot be overstated.
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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. |
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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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Clarke has been helping make communities more livable, safe and comfortable since 1946.
Learn more about our work in protecting public health on clarke.com.
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