August 30, 2021 | Week 33 | Volume 1 | Issue 7
Welcome to the Florida Disease Activity Update, from the desk of Dr. Jonathan Day! It is 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 the public from vector-borne diseases.
A QUESTION FROM READERS

Michaelene from Grants Pass, Oregon asks: "I recently read that there are several major outbreaks of Chikungunya virus around the world. Do I need to worry about my parents in Florida?"
 
A: I don’t think you need to worry. Chikungunya virus (CHIKV) is in the genus Alphavirus (the same genus as EEEV) and is transmitted primarily by Aedes aegypti and Ae. albopictus. As of the end of July, there were approximately 85,000 human cases reported worldwide by the European Centre for Disease Prevention and Control. Most of the cases are in Brazil and India. Even though rainfall in Florida has favored Ae. aegypti and Ae. albopictus reproduction, the drastic reduction in travel due to the COVID-19 pandemic reduces the chance of CHIKV reintroduction into Florida. Having said this, the first 2021 travel-related case of CHIKV in Florida was reported last week in Broward County, in a traveler from Brazil. Stay tuned.  
THE 2021 FLORIDA ARBOVIRAL TRANSMISSION SEASON TO DATE
Not much has changed this week. Groundwater saturation continues to be reported in most Florida counties. However, drying trends have begun to appear along the southeastern Florida coast from the Florida Keys north to Ft. Pierce, south of Orlando in central Florida, and the four counties in the western Florida Panhandle. These dry downs may favor the late-season amplification of WNV and SLEV in migrant birds.
In Florida, four mosquito-borne arboviruses currently account for the greatest human disease risk; dengue viruses (DENV), eastern equine encephalitis virus (EEEV), St. Louis encephalitis virus (SLEV), and West Nile virus (WNV). The current Florida transmission risk for each of these viruses is reviewed below.
WHAT ARE WE CURRENTLY SEEING?
Eastern Equine Encephalitis (EEEV) Activity
The transmission of EEEV seems to be dropping off, as is typically the case this time of year. 

Five (5) new EEEV antibody-positive sentinel chickens were reported during week 33, bringing the total number of chickens testing positive for EEEV antibody in 2021 to 166. The new positive sentinel chickens were reported in Citrus (1), Indian River (1), Nassau (1), and Volusia (2) Counties. The Indian River County EEEV situation is interesting. So far in 2021, Indian River County has reported eight sentinel chicken seroconversions to EEEV (none for WNV). This is an unusually high number of EEEV seroconversions for this County at this time of year. It may represent a landscape or vector switch favoring the transmission of EEEV. 
The number of EEEV-positive horses so far in 2021 remains at 14. The risk of a widespread epizootic in Florida horses for the remainder of 2021 is low, but the sporadic transmission of EEEV to horses remains a possibility.
The continued sporadic transmission of EEEV in the northern half of Florida indicates that the EEEV transmission season is not over. The area around Walton County remains a region of special concern for potential human EEE cases and additional transmission of EEEV to humans and equines. 

Find a review of 2020 EEEV activity in the archived Vol 1, Issue 1 report.
West Nile Virus (WNV) Activity
The sporadic transmission of WNV in Florida continues, but the threat of widespread WNV transmission to equines and humans currently remains low.
One (1) new WNV antibody-positive sentinel chicken was reported in Manatee County this week, bringing the total number of 2021 WNV sentinel chicken seroconversions in Florida to 19. All cases are in five Florida counties. This remains a low number of seroconversions compared with the Week 33 numbers from recent years.

Find a review of 2020 WNV activity in the archived Vol 1, Issue 1 report.
Dengue (DENV) Activity
The wet conditions in south Florida continue to favor the local production and dispersal of Aedes aegypti and Ae. albopictus, but it is difficult to initiate a transmission cycle in the absence of the pathogen. 
Find a review of 2020 DENV activity in the archived Vol 1, Issue 1 report. 
St. Louis Encephalitis Virus (SLEV) Activity
The transmission of SLEV in Florida remains extremely low. So far in 2021, only two sentinel chickens (both in Palm Beach County in mid-April) have tested positive for antibodies to SLEV. St. Louis encephalitis virus may no longer be endemic in Florida and the future transmission of this virus may be dependent on its reintroduction into the state. As with WNV, fall migration has the potential of seeding SLEV into Florida from the north. In addition, the fall migration will provide a large number of susceptible birds that may serve as amplification hosts to support a late-season SLEV transmission cycle. I saw the first wave of Chimney Swifts moving south this week. The appearance of migrating Barn Swallows will mark the official beginning of fall migration for me.
OPERATIONAL STRATEGIES TO CONSIDER
Vector and arbovirus surveillance remains one of the most important tools that vector control agencies currently have at their disposal. Arboviral transmission indices (sentinel chickens, positive equines, positive exotics (i.e., 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 provides added information about potential transmission risk. Additional vector control efforts in and around sites where virus transmission is known or suspected of recently occurring provides another potential mechanism to mitigate viral transmission.

The Florida regions with the highest current concern for arboviral transmission are those where indicators of EEEV transmission (sentinel chickens and EEE-positive equines) are currently high. These include: The Central Florida Counties around Orange County, all North Florida Counties, and the Panhandle Counties, especially those around Walton County.
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 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 and are posted at: fireweather.fdacs.gov/wx/kbdi_4km.html.

All of the graphics used in this Newsletter were designed and developed by Gregory Ross.
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