June 26, 2024 | Volume 4 | Issue 2 | As of Week 25 | |
Welcome to the Florida Disease Activity Update from the desk of Dr. Jonathan Day. | |
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.
New to Volume Four: Scroll down to view suggested readings to accompany today's Newsletter from Dr. Day.
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A QUESTION FROM OUR READERS | |
Q. Spencer from Merritt Island, FL, asks: “What species is this (Figure 1)?”
A. Aedes aegypti—The Yellow Fever Mosquito.
Q. JFD-Where were these collected?
A. Spencer-Inside our house, we had a whole colony breeding in our spare bedroom.
Q. JFD-In what?
A. Spencer- Figure 2.
Q. JFD-What was the landing rate?
A. Spencer- About three per minute.
JFD-Classic! Aedes aegypti is a domestic species that prefers to live inside homes and buildings, usually in buildings that are not air-conditioned. But as you have proven, they will take any opportunity to invade a home. Does anyone in your household have dengue, Zika, Chikungunya, or yellow fever?
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Figure 1. Mosquitoes collected inside Spencer’s house in Merritt Island, FL. | |
Figure 2. Larval habitat for mosquitoes collected inside Spencer’s house in Merritt Island, FL. | |
THE CURRENT OUTLOOK FOR ARBOVIRAL TRANSMISSION IN FLORIDA | |
What a difference a day makes! The most recent KBDI for our last Newsletter was June 9th, 2024 and appears below as Figure 3.
On June 12th, heavy rainfall was reported across the Florida Peninsula (Figure 4), changing the KBDI to what is seen in Figure 5.
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Figure 3. The KBDI values for June 9th, 2024. Red indicates extremely dry surface conditions bordering on severe drought. | |
Figure 4. Rainfall totals for June 12th, 2024 across the Florida Peninsula. | |
Figure 5. Florida KBDI values for June 15th, 2024. | |
This dramatic shift in South Florida surface water (Figure 6) may favor the amplification of WNV, but the virus appears to be missing in action (see below). | |
Figure 6. Florida KBDI values for June 24th, 2024. | |
Table 1 summarizes the current status of vector-borne disease transmission and pathogen introductions in Florida as of June 22nd, 2024. | |
Table 1. Summary of mosquito-borne disease transmission and imported cases in Florida as of June 22, 2024. | |
Dengue Viruses
So far in 2024, 237 travel-associated human dengue cases have been reported in Florida (Figure 7, Table 1, and Table 2). All four dengue serotypes have been reported as travel-associated cases in Florida (DEN 1 = 49 cases, DEN 2 = 41 (a dramatic increase from the last report), DEN 3 = 86 (also a large increase from the last report), and DEN 4 = 9). Thirty-two percent of the travelers were from Cuba, and 24% were from Brazil (the same as in the last report).
Eight locally-acquired dengue cases have been reported in Florida so far in 2024. Six were from Miami-Dade County, one from Pasco County, and most recently a case in Hillsborough County with infection in late May.
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Figure 7. The spatial distribution of travel-associated human dengue in Florida as of June 22, 2024. The 10 counties shaded red indicate areas of at least one travel-associated dengue case reported during the past three weeks and are areas where the introduction of dengue virus via an infected traveler may translate into locally-acquired cases in the coming weeks. | |
Eastern Equine Encephalitis Virus
Thirty-one EEEV antibody-positive sentinel chickens have been reported in Florida so far in 2024 (Figure 8). Eight EEE-positive equines have been reported in Florida so far in 2024 (Figure 9).
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Figure 8. The spatial distribution of EEEV antibody-positive sentinel chickens in Florida during the 2024 arboviral transmission season. | |
Figure 9. The spatial and temporal distribution of EEE-positive equines in Florida during the 2024 arboviral transmission season. | |
Malaria
Twenty-seven travel-associated human malaria cases have been reported in Florida during 2024 (Figure 10). Thirteen of the cases were Plasmodium falciparum, 13 were P. vivax, and one was P. ovale. The majority of travelers (78%) were from Africa.
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Figure 10. The spatial distribution of travel-associated human malaria in Florida as of June 22, 2024. The three counties shaded red indicate areas of at least one travel-associated malaria case reported during the past three weeks and are areas where the introduction of malaria via an infected traveler may translate into locally-acquired malaria in the coming weeks. | |
St. Louis Encephalitis Virus
A second sentinel chicken seroconversion to SLEV was reported this week in Pasco County. The first seroconversion was in Walton County in March. The SLEV has virtually disappeared from Florida with the exception of rare re-introductions, probably by migrating and dispersing wild birds.
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West Nile Virus
Seven WNV antibody-positive sentinel chickens have been reported in Florida during 2024. The most recent sentinel chicken seroconversion to WNV was reported in Palm Beach County during Week 17 (April 27th).
A summary of observed and expected numbers of travel-associated and locally-transmitted mosquito-borne viruses and diseases to date appears in Table 2.
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Table 2. Summary of expected and observed mosquito-borne disease infections in Florida reported during 2024 (as of 6/22/24). | |
OPERATIONAL STRATEGIES TO CONSIDER | |
Surface and groundwater conditions in Florida have been all over the map so far this season (Figures 3-6) making transmission prediction difficult. However, a couple of observations can be made.
First, this year, the transmission of EEEV has shifted further south than in the past (Figures 8 and 9). The five EEE-positive equines south of Orange County are unusual. All indications so far this season are that a large outbreak of EEEV is unlikely. However, the virus is clearly cycling in the mid-peninsula of Florida, where there is a probability of additional EEE-positive equines along with possibly human EEE cases. Public awareness is the best defense against future transmission of EEEV in Florida.
Second, where has WNV gone? It is behaving more like SLEV and less like the WNV we are so familiar with in Florida. Transmission of WNV in Florida is most prevalent from July to November, so the most intense transmission season is still in front of us, but it is difficult to have WNV amplification and transmission in the absence of the virus.
Finally, the locally-acquired dengue case in Hillsborough County this week indicates that there is a risk of local dengue transmission anywhere that Aedes aegypti and travel-associated human dengue cases overlap. As we continue to report record high temperatures and KBDI values in the deep-blue region of the scale, we will continue to see locally-acquired dengue in the Florida Peninsula.
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SUGGESTED READINGS FROM DR. DAY | |
As relevant to the contents of Newsletter editions and current events within the mosquito control sector, Volume Four will feature a selection of readings for readers to further explore.
An unprecedented outbreak of Lassa fever is currently ongoing across 28 states in Nigeria. So far in 2024, 897 confirmed cases and 162 deaths have been reported, with an exceptionally high case fatality rate of 18.1%.
Lassa fever, also known as Lassa hemorrhagic fever, is caused by the Lassa virus. Transmission is most prevalent across the Lassa belt in West Africa including the countries of Guinea, Nigeria, Sierra Leone, and Liberia. For years, the mode of transmission was unknown. Initially, transmission by an insect vector was considered a possibility, but that notion was quickly dispelled in favor of a rodent reservoir. It is now known that contact with the urine and feces of infected Natal multimammate mice (Mastomys natalensis) and human-to-human transmission are the primary modes of Lassa virus transmission.
Even though the Lassa virus is not vector-borne, it has a rich history in medical entomology lore. In the late 1960s, a large portion of the identification of this new virus was done at the Yale Arbovirus Research Unit in New Haven, CT, an offshoot of the Rockefeller Foundation. The principal players were Wilber Downs, the director of YARU, Jordi Casals, Sonya Buckley, and Bob Shope.
The first three non-native human infections in the first known Lassa fever outbreak were all nurses working at a small bush hospital in Lassa, Borno State, Nigeria. They were Laura Wine, Charlotte Shaw, and Penny Pinneo. Only Pinneo survived after being evacuated to Columbia Presbyterian Hospital in New York City. Her survival was incredibly important because after Jordi Casals was infected with the Lassa virus in a laboratory accident at YARU, Pinneo’s serum containing antibodies to the virus was harvested and administered to Casals, probably saving his life.
A fantastic summary of the early history and discovery of the Lassa virus can be found in John G. Fuller’s book: Fever! The Hunt for a New Killer Virus (1974, Reader’s Digest Press, New York, 297 pp.) (Figure 11).
If you would like to read one of the original papers describing the identification of Lassa virus, please see:
- Frame, J.D. et al. 1970. Lassa fever, a new virus disease of man from West Africa. I. Clinical description and pathological findings. Am. J. Trop. Med. And Hygiene 19:670-76.
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Figure 11. A great read if you can find it. | |
Jonathan Day, Professor Emeritus of Medical Entomology at the University of Florida and stationed at the Florida Medical Entomology Laboratory in Vero Beach 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, 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.
The Newsletter is edited and distributed by Linda McDonagh.
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