August 23, 2021 | Week 32 | Volume 1 | Issue 6
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 public health from vector-borne diseases.
A QUESTION FROM READERS

There was a report last week of a human death in New Hampshire caused by Jamestown Canyon virus (JCV). Is there a risk of JCV transmission in Florida?    
 
A: Jamestown Canyon virus is a California Group virus, in the genus Orthobunyavirus. Mosquito vectors include species in the genera Aedes, Coquillettidia, Culex, and Culiseta. Large mammals, including white-tailed deer, moose, and bison, serve as amplification hosts. An average of 15 neuroinvasive cases of JCV are reported annually in the United States. From 2010 through 2019, most of the human cases were reported in Minnesota (37), Michigan (72), and New England (20). There has never been a human case of JCV reported in Florida. 
THE 2021 FLORIDA ARBOVIRAL TRANSMISSION SEASON TO DATE
Groundwater saturation continues to be reported in most Florida counties. The only exceptions are the four western counties in the Florida Panhandle and the upper Florida Keys. These conditions will continue to favor mosquito production (especially container-breeding Aedes mosquitoes) and mosquito dispersal. Because of the extensive groundwater saturation, mosquitoes are free to disperse and breed in virtually all Florida habitats. This favors the continued sporadic transmission of mosquito-borne arboviruses throughout the state. 
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
There is continued evidence of low-level EEEV transmission in North Florida and in the Florida Panhandle. 
 
Eight (8) new EEEV antibody-positive sentinel chickens were reported during week 32, bringing the total number of chickens testing positive for EEEV antibody in 2021 to 161. The new positive sentinel chickens were reported in Bay (1), Hillsborough (1), Leon (2), Nassau (1), and Walton (3) Counties. Conditions favorable for the transmission of EEEV remain in place throughout the northern half of the state. 
Two (2) new EEEV-positive horses were reported in Florida during Week 32 (see map). The first was reported in Walton County (onset 7/25/21, infected around 7/20/21). The number of EEEV antibody-positive sentinel chickens in Walton County (54 to date) indicates that the virus is circulating and being transmitted at a high rate in this county. The second EEEV-positive horse was reported in Duval County (onset 8/6/21, infected around 8/1/21).
The continued sporadic transmission of EEEV in North Florida and the Florida Panhandle 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 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 has started to pick up in Florida, but the threat of widespread WNV transmission to equines and humans currently remains low.

Seven (7) new WNV antibody-positive sentinel chickens were reported during Week 32. Four (4) new positives were reported in Lee County, one (1) in Pinellas County, and two (2) in Walton County bringing the total number of WNV antibody-positive sentinel chickens reported in Florida during 2021 to 18. This remains a low number of seroconversions compared with the Week 32 numbers from recent years.

Find a review of 2020 WNV activity in the archived Vol 1, Issue 1 report.
Dengue (DENV) Activity
As of Week 32, there has been no indication of locally-acquired dengue infection in Florida during 2021. Five (5) travel-related dengue cases have been reported in Broward (1), Hillsborough (1), Miami-Dade (1), and Palm Beach (2) Counties. This is a historically low number for mid-August and may be an indication of reduced travel and tourism resulting from the COVID-19 pandemic.
 
Table 1 summarizes the number of travel-related human DENV cases reported in Florida as of Week 32 for 2012 to 2021. The range of reported cases for the 10-year data set is 5-91 and the annual average of travel-related cases reported in Florida by Week 32 is 34.3. We are on the low end of the number of reported cases and it will be difficult to initiate a local transmission cycle with so few travel-related cases entering the state.
The wet conditions across Florida continue to favor 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. It is evident from Table 1 that even low numbers of travel-related introductions of DENV may result in local transmission (i.e., 14 introductions in 2018). However, a high number of travel-related introductions of DENV increases the probability that a viremic traveler may encounter a susceptible mosquito vector.

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) 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.
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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