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Florida Medical Entomology Laboratory

Florida Medical Entomology Laboratory

Florida in 2004: Hurricanes, Mosquitoes and West Nile

As of August 2004, West Nile virus transmission was sporadic in Florida just as in previous years. The Miami-Dade region had the most focal transmission to humans, particularly in the Coconut Grove area. Jon Day and I, working with Marlon Nelms and Miami-Dade Mosquito Control used the FMEL Arbovirus Rapid Deployment System (ARDS) to collect Culex nigripalpus in this area during early August, in an attempt to measure transmission. Fortunately, we did not detect transmission in the several hundred Cx. nigripalpus we collected. We concluded transmission frequencies at that time were too low to cause more then the sporadic cases being observed, and that a large outbreak was unlikely. Miami-Dade was on Medical Alert and Miami-Dade Mosquito Control continued to monitor the situation closely and apply control measures. Florida was again spared the "big event" West Nile epidemic.

There were large mosquito populations in some regions of Florida due to August rains. Many Florida mosquito control districts recorded large mosquito populations with some nightly Cx. nigripalpus trap collections in the 1000s. Thankfully, these large numbers occurred in late August. There was little West Nile virus amplification preceding the August collections due to the extremely dry summer conditions and we did not see an increase in West Nile transmission as a result.

And then hurricane time! As if the destruction to homes, livelihoods and well being caused by Florida's hurricanes were not enough in 2004, the mosquitoes quickly followed as expected, and they came with a vengeance. The large amounts of flood water produced huge numbers of flood water mosquitoes in many areas of Florida, followed by other species from the standing water that could not drain properly.

What occurred first with Hurricane Charley became the typical pattern in larger areas of Florida impacted by Frances, Ivan and Jeanne. Many people with home damage, damaged screens, walls and roofs, were more exposed to mosquitoes. Electricity was off for many days in some areas. Increased exposure to the mosquitoes added to the misery level. The flood water mosquitoes like Psorophora species, Aedes vexans, Ochlerotatus taeniorynchus, etc., came first. Counts of 20,000 or more in a trap night were not uncommon. This was quickly followed by species like Cx. nigripalpus with 20,000 per trap being typical. Mosquito control districts in affected areas acted quickly to suppress populations. An amazing feat since the personnel in the districts were at the same time also contending with the personal problems associated with the storm, damage to their equipment and facilities. These dedicated individuals still worked long hours to conduct effective mosquito control. This situation occurred in many counties throughout the state in 2004. In counties like Desoto, Hendry and Hardee, counties hard hit and with no organized mosquito control, the Florida Department of Agriculture and Consumer Services (DACS), with assistance from FEMA funds, launched an unprecedented county by county aerial spray campaign to quickly reduce the numbers of mosquitoes assaulting the hurricane victims. DACS personnel collected surveillance data on mosquito numbers and targeted areas for spraying based on the record numbers of mosquitoes being observed. After each storm, more counties were put on the spray list - a tremendous effort that continued into October in some areas.

Several things come to mind in looking back on 2004 and Florida Mosquito control.

  1. No one could have anticipated the magnitude of the mosquito problem associated with four consecutive hurricanes, two having almost identical tracks.
  2. Florida mosquito control and DACS did a tremendous job in providing mosquito control at a time when Floridians were being exposed to large numbers of biting mosquitoes.
  3. Thankfully the arrival of the storms in Florida was preceded by environmental conditions that were not favorable to West Nile or other arbovirus amplification.
  4. Thankfully the arrival of the September storms was too late in the mosquito arboviral transmission cycle to permit efficient amplification of West Nile virus despite the unprecedented number of vector mosquitoes.

Florida appreciated the federal support of FEMA that was managed by DACS for mosquito control in the aftermath of the hurricanes. I hope that similar funding will be forthcoming to reduce the impact of a devastating emergency situation that will result during a future Florida West Nile "big event" epidemic when 100s or 1000s of human West Nile cases will be reported. Our common goal in Florida is to predict this emergency in advance, and then quickly apply effective, efficient and proper mosquito control and public health communications to mitigate the epidemic. With continued support and research we can provide information and appropriate advance warnings similar to hurricane tracking and forecasting, so that mosquito control and public health efforts are focused to do the most good. Florida mosquito control can be proud of providing effective mosquito control that contributed greatly to reducing pest mosquitoes and making life more bearable for our citizens during this extraordinary hurricane period. Well done. We can do the same to predict and mitigate future arboviral epidemics in Florida.

Walter J. Tabachnick - Retired
Florida Medical Entomology Laboratory
University of Florida/IFAS