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Florida Medical Entomology Laboratory

Florida Medical Entomology Laboratory

A West Nile Virus Positive Bird: WN Response by the Numbers

There are many questions about West Nile (WN) virus for Florida Mosquito Control and Florida Public Health Agencies. When will the first WN positive birds be found in Florida? Where? What will it mean in terms of public health risk? What will be the appropriate control responses? How will the public and media perceive mosquito control and public health responses? Will the responses be effective, efficient and proper?

I imagine that a common refrain in many Florida Mosquito Control District Offices is "Please, don't let it be me." This is understandable. The first positive birds will place the local organization on the front burner of a very difficult situation. So what to do? We need public discussions that will assist those on the front burner to take appropriate actions.

Imagine you are the unlucky control district at WN Ground Zero, and the Tampa laboratory's PCR has identified a bird from your District as WN positive. The lab has notified you just a few days after submitting the birds for testing. Congratulations, now what? There will be a flurry of notifications and news reports. The headlines will read "WN virus arrives in Florida." However, now decisions are needed concerning the vector targets, methods and areas for mosquito control, and the information about personal protection to the public. All responses will depend on the answers to these questions:

  1. Was the bird infected in the region where it was collected?
  2. Did the bird contain virus, or only PCR nucleic acid?
  3. What is the evidence for mosquito transmission in the region?
  4. What is happening in the region and in surrounding regions concerning mosquito populations?
  5. What mosquito species are currently active in the regions, and how do populations compare to previous years?
  6. Is it likely that WN virus amplification will occur in the region? In surrounding regions?
  7. What is the likely time frame for amplification based on estimates of the regions bird and mosquito populations.
  8. What steps can be taken to monitor real time transmission in the region using animal sentinels? Chickens? Horses? Other sentinels?
  9. What is the risk for human transmission? Isolated cases? The big event--a WN epidemic with hundreds of cases?

I hope that those on the front line in Florida will rely on the expertise at the FMEL. We encourage those with information and concerns to contact the laboratory and the FMEL Encephalitis Information System (EIS) team ( for consultation in planning and evaluation. We want to assist in addressing these questions and arriving at the appropriate responses.

We need to be prepared.

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