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. Yes, I have observed Culex mosquitoes feeding on manatees along the shore of a black mangrove forest just after sunset. The manatees appeared to be resting.

Mosquitoes feed on a large selection of aquatic and semi-aquatic vertebrates including marine mammals, frogs, fish, alligators, snakes, and turtles. One of the first papers I published after arriving at the FMEL was Day and Curtis, 1983 dealing with Aedes taeniorhynchus blood feeding on nesting sea turtles. In 2020, Reeves and Gillett-Kaufman published a masterful review of mosquito blood feeding on marine and aquatic vertebrates. In that paper, they review publications dealing with arboviral infections in Orcas in Florida (SLEV) and Texas (WNV). Both infections resulted in the death of the whales.

Perhaps the ultimate example of odd blood feeding behavior by mosquitoes was published by Reeves et al. in 2018. In this paper, the authors report that Uranotaenia sapphirina feeds on earthworms and leeches (Figure 1). Many mosquito species are truly opportunistic in their quest for a protein source for egg development. I once observed a Cuban Tree Frog that crawled into a CO₂-baited lard can trap. In the morning there were many blood fed Culex nigripalpus along with one very desiccated frog.

One new WNV-positive equine was reported in Hillsborough County this week with a likely infection date in mid-October. Two new EEEV antibody-positive sentinel chickens were reported in Orange and Walton Counties (Table 1). Three new travel-related malaria cases were reported this week in Flagler (1) and Miami-Date (2) Counties. One new locally-acquired dengue case was reported in Miami-Dade County bringing the total number of locally-acquired dengue cases in Florida to 36. Fifty new travel-related dengue cases were reported, 40 in Miami-Dade County (Figure 2). There were no new reports of HJV or SLEV transmission. The risk of EEEV, HJV, and SLEV transmission in 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.

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. We are rapidly approaching the time of year when the risk of a widespread outbreak of human WN is unlikely. 

The only reasonable way to reduce the number of locally-acquired dengue cases in Florida is to reduce Aedes aegypti and Ae. albopictus populations. Every home in South Florida has an associated population of these two efficient disease vectors. A single travel-related dengue case coming into a neighborhood dramatically increases the likelihood of infecting local mosquitoes and starting a round of local dengue transmission. Source reduction and public education are two techniques that will begin to reduce the number of dengue infections originating in Florida.

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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