November 22, 2021 | Week 45 | Volume 1 | Issue 19 |
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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.
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What's Ahead for this Newsletter?
This will be the last weekly Newsletter for the 2021 arboviral transmission season unless something very unusual happens before the end of the year. A Year-End Summary for the 2021 Florida Arboviral Transmission Season will be published as Volume 1, Issue 20 on 1/5/22.
Looking ahead to 2022, the Newsletter will continue! In late May 2022, we will publish a Year in Review for 2021, which will include additional information about malaria, Zika virus, and Chikungunya virus activity. We will resume weekly Newsletter updates for the 2022 arboviral transmission season in June. We continue to welcome your feedback and reader questions for future issues. Thank you for your readership and continued interest in this Newsletter!
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Mora from Vero Beach, FL asks: “Of the four major North American West Nile Virus vectors (Culex pipiens, Cx. quinquefasciatus, Cx. tarsalis, and Cx. nigripalpus), Cx. nigripalpus seems to be an outlier. What makes Cx. nigripalpus different from the other WNV vectors?”
A: First, Culex nigripalpus has a much narrower distribution in the continental USA than the other three species. Cx. nigripalpus is a tropical/subtropical floodwater Culex that prefers to oviposit (lay eggs) in freshly flooded habitats including, but not limited to, roadside ditches and agricultural furrows. The species is distributed along the southeast Atlantic coast from North Carolina through all of Florida, along the Gulf Coast to Texas, Mexico, Central America, northern South America, and throughout the Caribbean Basin.
Second, Cx. nigripalpus are very sensitive to weather conditions. Populations spike in correlation with the rainy season and are highly susceptible to drought. In Florida, adults appear in significant numbers at the beginning of the rainy season in May, build through the summer, and peak in September and October. The number of adults begins to decline at the beginning of the dry season in November. During severe drought years in Florida's history like 1985, 1986, and 1987, the species was virtually absent from the state. Adults of this species are also very sensitive to humidity and flight activity is greatly reduced when the relative humidity falls below 90 percent.
Finally, the blood-feeding behavior of this species changes abruptly from birds in the winter and spring to mammals in May and June. Mammals remain the preferred hosts until mid-winter. This is one of the reasons that Cx. nigripalpus is an excellent vector of EEEV, SLEV, and WNV in Florida and throughout its range.
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THE WEEK IN REVIEW:
ARBOVIRAL TRANSMISSION IN FLORIDA
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Low-level background transmission of EEEV, SLEV, and WNV continued in Florida during Week 45 of the 2021 arboviral transmission season, including:
- One EEEV antibody-positive sentinel chicken.
- One SLEV antibody-positive sentinel chicken.
- Five WNV antibody-positive sentinel chickens and one human WNV-positive asymptomatic blood donor.
West Nile continues to be the only mosquito-borne virus that currently threatens humans and equines in Florida.
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WHAT ARE WE CURRENTLY SEEING? |
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Eastern Equine Encephalitis (EEEV) Activity
One (1) EEEV antibody-positive sentinel chicken was reported in Walton County during Week 45, bringing the total number of EEEV antibody-positive sentinel chickens reported in Florida during the 2021 arboviral transmission season to 181. This is well above the 11-year (2010-2020) annual Florida EEEV seroconversion rate of 101 per year.
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Find a review of 2020 EEEV activity in the archived Vol 1, Issue 1 report.
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West Nile Virus (WNV) Activity
Five (5) new WNV antibody-positive sentinel chickens were reported during Week 45 in Lee, Pasco, Pinellas (2), and Sarasota Counties. This brings the total number of WNV-positive sentinel chickens reported in Florida during 2021 to 133, well below the 11-year (2010-2020) annual seroconversion rate of 408 per year. There was also a WNV-positive human asymptomatic blood donor reported in Columbia County this week. The individual was likely infected with WNV in mid-October. There is still active WNV transmission in Florida and the area of greatest concern for human transmission remains Central and North Florida and all of the Florida Panhandle.
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Find a review of 2020 WNV activity in the archived Vol 1, Issue 1 report. |
Dengue (DENV) Activity
A new travel-associated dengue case was reported this week in St. Lucie County, bringing the total number of travel-associated dengue cases reported in Florida during 2021 to 12.
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Find a review of 2020 DENV activity in the archived Vol 1, Issue 1 report.
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St. Louis Encephalitis Virus (SLEV) Activity
One (1) new SLEV antibody-positive sentinel chicken was reported in Nassau County during Week 45, bringing the total number of SLEV antibody-positive sentinel chickens reported in Florida during 2021 to 15.
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Find a review of 2020 SLEV activity in the archived Vol 1, Issue 1 report.
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OPERATIONAL STRATEGIES TO CONSIDER |
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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 WNV transmission (sentinel chickens and WNV-positive equines) continue to be reported. These include counties from Central Florida, North Florida, and the Florida Panhandle, especially the counties surrounding Walton County.
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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.
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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 issues of this Newsletter are designed and developed by Gregory Ross.
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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.
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