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A: The Florida Sentinel Chicken Arboviral Surveillance Program began in 1977 as a backyard chicken surveillance effort in response to an ongoing SLE epidemic in South Florida. In 1978, the current, more formal program was introduced throughout the state, with some counties maintaining sentinel chickens at the same location since then.

A great deal has been learned during this 45-year program. The number of chickens per flock has varied between two and twelve, with six determined to be the optimal number for ease of flock maintenance and surveillance sensitivity. While bleeding frequency can vary from once a month to once a week, bleeding all sentinels once a week is ideal as this allows the calculation of the narrowest infection windows for positive birds.

In light of the Vacutainer supply chain problem, I would first reduce flock size from six to four. Then, I would go to an every other week bleeding schedule until a positive chicken is reported from one of your flocks. As soon as a positive chicken is reported, I would bleed every bird in the positive flock once a week. After four consecutive weeks of negative reports, I would resume the every other week bleeding schedule.

Once the Vacutainer supply issue is resolved, I would return to six birds per flock with weekly bleedings for the remainder of the arboviral transmission season (May-October).

Florida mosquito-borne disease transmission and vector-borne disease pathogen introductions have remained extremely low in 2022. For locally-transmitted disease pathogens, this is likely partly due to the rainfall patterns reported in Florida during the first five and a half months of 2022. 

The ideal groundwater levels for a heavy eastern equine encephalitis virus

(EEEV) transmission year (1991) and a St. Louis encephalitis virus (SLEV) epidemic year (1990) are shown below with arrows indicating where we currently are in 2022.

In Week 19 (mid-May), we are currently at a point where conditions should be drying to support a heavy EEEV transmission year. For heavy West Nile virus (WNV) transmission, we are currently at a point where there should be a deep drought in areas where WNV amplification and transmission will eventually appear. The current KBDI conditions for Florida are shown in Figure 2 below.

Parts of the Florida Panhandle and North Florida are currently drying, which may favor EEEV transmission, but it is late in the arboviral transmission season for significant EEEV amplification and transmission to occur.

Parts of South Florida and the Central Peninsula remain extremely dry while other parts of the peninsula - the Gulf Coast counties from Lee County north to Citrus County - have experienced significant wetting during the past two weeks. This may favor WNV transmission in late May and June. In particular, Lee County is currently an area of special concern.

As of Week 19 in 2022, the following mosquito-borne disease transmission events and pathogen introductions have been reported:

The transmission of EEEV has been extremely slow to start so far in 2022. Most of the sentinel chicken seroconversions to EEEV have been in the Central Florida counties surrounding Orlando.

Travel-related introductions of DENV and Malaria have been slow to start in the 2022 transmission season.

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 (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 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 potential mechanism to mitigate viral transmission.

Specific operational strategies will be discussed during the 2022 arboviral transmission season depending on where and when vector-borne disease transmission becomes evident in the state of Florida.

There is currently a moderate risk of arboviral transmission in some parts of Florida. It is important to note that arboviral transmission risk is never zero. The dry conditions in the central Florida Peninsula and the recent wetting along the Gulf Coast of the peninsula may favor WNV amplification and transmission later in the summer. May and June are the peak months of avian nesting season in Florida and what happens during the next two months may determine the intensity of WNV transmission in July, August and September. 

It will also be important to monitor travel-related dengue cases introduced into South Florida during the next three months. High numbers of travel-related cases may translate to an increased risk of locally-transmitted DENV during the summer of 2022.

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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