September 13, 2021 | Week 35 | Volume 1 | Issue 9 |
|
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.
|
|
Marianne from Vero Beach asks: “What is the difference between an epidemic, an epizootic, and an outbreak of a vector-borne disease?”
A: An epidemic is a regional outbreak of human disease beyond what is normally expected. For example, there have been 738 clinical cases of St. Louis encephalitis (SLE) reported in Florida since 1952 for an average of 11 per year. That makes 1959 (70 cases), 1961 (25), 1962 (222), 1977 (140), 1980 (12), and 1990 (226) SLE epidemic years for Florida.
Likewise, an epizootic is a regional outbreak of animal disease above what is normally expected. There have been 2,455 eastern equine encephalitis (EEE)-positive horses reported in Florida since 1982 for an average of 61 per year. Equine epizootics caused by EEEV were reported in 1982 (202), 1983 (117), 1991 (160), 2003 (207), and 2005 (150).
Outbreaks occur when case numbers below the epidemic/epizootic thresholds are reported. For example, Florida human SLE outbreaks were reported in 1993 (8) and 1997 (9).
|
|
THE 2021 FLORIDA ARBOVIRAL TRANSMISSION SEASON TO DATE |
|
Week 35 was another quiet week in Florida relative to vector-borne disease transmission. Most of Florida continues to be very wet. There continues to be a coastal drying trend from the Florida Keys to Miami and north to Ft. Pierce. There are also large dry-downs reported in central Florida south of Orlando and in northeast Florida west of Jacksonville. These dry downs may favor the late-season amplification of WNV and SLEV in migrant birds, but the risk of a widespread outbreak of WNV or SLEV in Florida is rapidly disappearing.
|
|
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). Human outbreaks caused by these arboviruses typically occur in early summer (DENV and EEEV) or late summer/early fall (WNV and SLEV), so the window for a large Florida outbreak caused by any one of these viruses is closing. 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 is ramping down, which is what we typically see during this time of year.
One (1) new EEEV antibody-positive sentinel chicken was reported last week in Walton County, bringing the total number of EEEV-antibody sentinel chickens reported in Florida during 2021 to 169.
There were no new EEEV-positive horses reported in Florida during Week 35 and the number of positive horses remains at 15.
|
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
Two (2) new WNV antibody-positive sentinel chickens were reported this week, one in Bay County and one in Walton County, bringing the total number of positive sentinel chickens to 43 for the 2021 transmission season.
|
The focus of WNV transmission in Florida continues to be along the west coast of the Florida Peninsula and in the central Florida Panhandle.
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 the initiation of a local transmission cycle will not be possible in the absence of the virus. A widespread and extensive outbreak of human dengue transmission in Florida is unlikely at this time.
|
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. Small migratory waves of warblers have started to move south along the east coast of the central Florida Peninsula.
|
|
|
|
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.
|
|
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.
|
|
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.
|
|
|
|
|
|
|
