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. Jorge from Vero Beach, FL asks: “How do hurricanes affect vector-borne disease transmission cycles?”

A. Last week we discussed how hurricanes have an immediate impact on vector-borne disease transmission cycles. This week we will explore the long-term impacts of hurricanes on transmission cycles. 

The most obvious impact of the hurricanes was to severely fragment hardwood forests. This reduced avian nesting sites and habitats for ground-feeding birds. Before 2004 there were six breeding pairs of Northern Cardinals at our FMEL study site. Cardinals did not resume breeding at the FMEL until 2010 when a single breeding pair was observed. Only recently have multiple breeding pairs of cardinals returned to the hardwood forests surrounding the FMEL. Habitat destruction, fragmentation, and long-term modification by hurricanes are probably the most important impacts that hurricanes have on vector-borne disease transmission cycles. 

The impacts of Hurricane Ian continue to be felt in Southwest Florida and may influence the vector-borne disease cycles there for years to come (see this week’s Question From Our Readers). Some arboviral surveillance programs and the FDOH Bureau of Public Health Laboratories in Tampa have rebounded while other surveillance programs may be done for the year. 

Forty-one new WNV antibody-positive sentinel chickens were reported in Florida last week (Figure 3). Three new locally-acquired dengue cases were reported in Miami-Dade County, bringing the total number of locally-acquired dengue cases in Florida to 30. Sixty new travel-related dengue cases were reported in South Florida last week (Figure 4). There were no reports of EEEV, HJV, or SLEV transmission in Florida last week. The risk of transmission for all three of these viruses in South Florida is currently low, 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. 

As of Week 41, 2022, the following mosquito-borne disease transmission events and pathogen introductions have been reported in Florida:

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.

The current risk of WNV transmission remains high in some regions of Florida and low in others (Figure 3). Transmission in Southwest Florida has likely been interrupted by Hurricane Ian. The risk of WNV transmission on the fringe of the hurricane and in the Florida Panhandle is currently moderate to high. 

The 30 locally-acquired dengue cases and the continued reports of travel-related dengue in South Florida (43 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. The three new cases of locally-acquired dengue reported during Week 41 were all infected in September and the risk of continued dengue transmission in South Florida remains high. 

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.

Learn more about our work in protecting public health on clarke.com.