It continues to be 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.

An archive of all past newsletter issues remains available on the Clarke website.

For example, horse flies, deer flies and black flies have mouthparts that work like scissors and a sponge. The scissors make a cut in the skin and the tongue laps up the blood. Mosquito mouthparts act like a scalpel and a straw; the cutting parts make a small incision in the skin through which a hollow tube is inserted. A pump in the mosquito’s neck creates a negative pressure and blood is drawn into the mosquito’s midgut. Mosquitos are “clean feeders” that leave no blood on their exterior mouthparts. In contrast, horse, deer, and black flies are “dirty feeders” that contaminate their entire head with blood during feeding. Because of this contamination, dirty feeders are able to transmit viruses directly from one host to another in a process known as mechanical transmission. Disease transmission by contaminated hypodermic needles is a form of mechanical transmission. Equine infections anemia is a retrovirus that is mechanically transmitted from horse to horse by biting flies.

Diseases transmitted by mosquitoes include malaria (a protozoan), dog heartworm (a nematode) and West Nile (a virus). The pathogens that cause these diseases must complete a reproductive cycle inside the mosquito before they can be transmitted to additional hosts. This is referred to as biological transmission. Pathogen reproductive cycles in the mosquito are temperature-dependent; the higher the environmental temperature, the faster the mosquito becomes infected and is able to transmit the pathogen to a new host. For example, it takes a mosquito approximately two weeks to become infected after taking a blood meal containing West Nile virus.

There were 28 travel-related dengue introductions into Florida last week, 14 of which were in Miami-Dade County (Figure 2). A second locally-acquired dengue case was reported in Miami-Dade County last week. It is evident that local mosquitoes (probably Aedes aegypti) have been infected with DENV and are transmitting the virus to susceptible individuals in South Florida. The full extent of this outbreak remains to be determined. 

Figure 2. Travel-related dengue introductions in Florida during 2022. Counties in blue indicate introductions during 2022. Counties in red indicate the total number of dengue introductions in 2022 and recent introductions during Week 30.

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 such as 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 mechanism to mitigate viral transmission.

There is currently a low risk of EEEV transmission in Florida. 

There is currently a low risk of WNV transmission in Florida. Arboviral surveillance and reporting during the next weeks will help to determine the current situation relative to the transmission of EEE and WN viruses throughout the state.

There is currently a moderate to high risk of local dengue transmission in South Florida (Figures 2 and 3). The appearance of two locally-acquired dengue cases in Miami-Dade County in June and July and the continued influx of travel-related dengue cases into South Florida increase the risk of a local outbreak. As of now, Miami-Dade County is the most likely spot for such an outbreak. Increased Aedes aegypti control in areas surrounding locally-acquired and travel-related dengue cases will help to reduce potentially infected vector mosquitoes. Source reduction, the emptying, and where possible the destruction, of all water-holding containers remains the most productive control method against the likely dengue vector, Aedes aegypti. Cryptic Ae. aegypti breeding habitats remain a huge problem in places where this species is abundant. The location of these cryptic habitats remains one of the primary challenges for vector control agencies dealing with dengue outbreaks. 

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.

Learn more about our work in protecting public health on clarke.com.