GIVE

Florida Response Levels to West Nile Virus Detection: Options for Mosquito Control

Summer in Florida for 2001 means the mosquito season is upon us. It is time to encourage mosquito control professionals to make concerted efforts to collect dead birds and to report the collections to the FWCC and DOH (http://wld.fwd.state.fl.us/bird/) for transport to the Kissimmee and/or Tampa Laboratories. The Florida WN wild bird surveillance program is our first line of defense in our system to detect the entry of the virus into the State.

I have stated in previous Buzz Word columns that the detection of a WN positive bird in Florida can indicate different things and must be assessed in the context of the method of testing, and several other factors, like mosquito population data, numbers of positives, and indicators of actual local virus transmission. The Florida Department of Health, and Department of Agriculture and Consumer Services, Florida West Nile Virus Response Plan contains four levels to guide the response options when WN is detected. The response levels in the plan are:

  • Level 1: Initial detection of WN virus nucleic acid or antibody in sentinel flocks,wild birds or mosquitoes in a particular region of the state.
  • Level 2: Widespread detections in sentinel flocks, wild birds or mosquitoes.
  • Level 3: Detection of 1 or more human cases with Florida-acquired WN virus.
  • Level 4: Determination of widespread distribution of human cases or occurrence of WN virus detection in conjunction with a weather-related disaster (e.g., hurricane or flooding event).

The Florida West Nile Virus Response Plan recommendations for each level that are relevant to Florida Mosquito Control Districts are:

  • Level 1: The lowest level of recognition. Mosquito control should maintain control activities already in place, submit dead birds for testing, and maintain mosquito surveillance activities already in place.
  • Level 2: Indicators of transmission should result in increased levels of surveillance, more sentinels should be placed, and DACS will consider the need to declare an emergency to increase mosquito control activities in certain regions with consideration for requesting external resources for use in aerial adulticiding.
  • Level 3: DACS will declare an emergency and recommend increasing mosquito control activities in specified regions. Aerial adulticiding would be recommended based on the likely impact on suspect vectors, requests would be recommended to other agencies with aerial adulticiding capability as appropriate.
  • Level 4: Implementation of the Florida Emergency Operations Center to coordinate responses and request for vector control assistance in specific regions.

In keeping with several previous BuzzWords columns I have written on the meaning of different surveillance tools, I would recommend that Florida mosquito control pay attention to the details of the information being provided during WN surveillance. I believe mosquito control response levels might be as follows:

  • Level 1: WN antibody or nucleic acid in wild birds. Little risk, questionable that live virus is present. The lowest level of recognition.
  • Level 2: WN in sentinel flocks (virus isolation, antibody, or PCR) or a wild bird (virus isolation). Clearly indicates the virus is present in the region with local transmission. See Level 2 in the Florida Response Plan above.
  • Level 3: WN virus in wild birds, sentinel flocks, horses and vector mosquitoes - transmission at levels suggesting human risk for infection via mosquitoes. There is risk to humans. Consideration of Level 3 as in the Florida Response Plan above.
  • Level 4: 1- 20 human cases with Florida acquired WN virus. Increased and substantial risk to humans. Clearly an emergency and maximum mosquito control effort is required.
  • Level 5: Greater than 20 human cases in a county. An epidemic, and great risk for a big event.

The Florida Medical Entomology Laboratory is prepared to work with mosquito control to assess WN surveillance information. Stay tuned to the FMEL Encephalitis Information System at: http://eis.ifas.ufl.edu/.

We will all need to work together to determine when the information warrants moving to the next response level and what specific options are available to each mosquito control unit to bring to bear as appropriate.

Walter J. Tabachnick, Ph.D., Director
Florida Medical Entomology Laboratory