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Florida Medical Entomology Laboratory

Florida Medical Entomology Laboratory

Tough Choices for West Nile Virus Surveillance Programs

Loyal readers of BuzzWords are likely familiar with issues related to West Nile virus (WNV) surveillance and the related issues of decision making for mosquito control agencies. Over the past years there have been many BuzzWords columns on these subjects. In a recent issue of BuzzWords, with the help of Matt Yates of East Baton Rouge Mosquito Control District, we discussed the various advantages and disadvantages of using sentinel chickens and mosquito pools as arboviral surveillance tools (Yates, M. 2006. A Louisiana perspective on sentinel chicken surveillance for West Nile Virus. BuzzWords 6(6): 7-11; Tabachnick, WJ and JF Day. 2006. Sentinel chicken surveillance for West Nile virus. BuzzWords 6(6): 9-10.

Under the best of circumstances, I believe it is clear that surveillance for WNV is best served by a multi-pronged approach consistent with our knowledge that the surveillance options available to us provide different strengths and different types of information. For example, a tool that might be appropriate in one circumstance is not always the best tool to use. We have discussed often that mosquito pools will provide the best chance to detect the presence of WNV in an area, but may not provide realistic information that is useful for gauging the risk of human cases or mosquito transmission to humans. Although sentinel chickens provide a gauge for assessing transmission and human risk, there can be a long time lag between the actual transmission event and the appearance of a seropositive chicken. This time lag may be unacceptable in some circumstances. Hence, a combination of mosquito pooling and sentinel chicken arboviral surveillance should be considered, and there are times when one should move quickly from one type of surveillance to the other.

Unfortunately, the best of circumstances is not always a realistic possibility. At a recent meeting I was approached by two mosquito control directors from two states outside (thankfully) of Florida and presented with the following dilemma. Both individuals advised that their respective counties were cutting the resources for WNV surveillance and they could not support both mosquito and sentinel chicken surveillance programs.

I advised that this certainly placed them both in a difficult situation. I also advised that whatever their decisions were on the arboviral surveillance tool they eventually chose, the decision should be based on fulfilling their clearly stated and accepted goals for surveillance in the most cost effective manner possible. Certainly a starting point would be for each organization to have an estimate of the full costs of a complete mosquito surveillance program. This estimate should include the number of mosquitoes that would need to tested, costs of the tests, labor etc. This estimate should be weighed against the cost of a sentinel chicken surveillance program that will provide the same surveillance and risk information. Cost estimates should include the number of chickens, their maintenance, cages, labor, and costs for testing. Clearly the point here is to conduct a program that provides the biggest bang for the dollar. Unfortunately this reduction in surveillance effort may not be the best of circumstances, but the challenge is to not expend resources on either an under-funded mosquito surveillance program, or an under-funded sentinel chicken surveillance program neither of which will ultimately serve a county's arboviral surveillance needs.

Rather than repeating information on these topics here, I direct interested readers to review other BuzzWords columns that explain these issues. Readers can access past BuzzWords at:

Below is a list of some additional BuzzWords references on these topics that may assist readers in making the tough decisions:

  • Tabachnick, W. J. 2006. Mosquito surveillance and West Nile prediction: Lessons learned. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 6(4): 9-10
  • Tabachnick, W. J. & Day, J. F. 2006. Sentinel chicken surveillance: Some pitfalls in analyzing the data. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 6(5): 7-9
  • Tabachnick, W. J. & Day, J. F. 2006. Sentinel chicken surveillance for West Nile virus. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 6(6): 9-10.
  • Tabachnick, W. J. 2005. A Florida mosquito control arbovirus response plan. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 5(1): 5-6.
  • Tabachnick, W. J., Day, J. F. & Rutledge, C. R. 2005. Florida West Nile surveillance: Estimating mosquito transmission frequencies. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 5(2): 6.
  • Tabachnick, W. J. 2005. Florida West Nile Surveillance: estimating mosquito transmission frequencies. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 5(2):6.
  • Tabachnick, W. J. 2004. Florida's sentinel chicken surveillance program: Smart chickens. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 4(1): 7-8.
  • Tabachnick, W. J. 2004. Sentinel surveillance and human risk for West Nile. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 4(2): 10-12.
  • Tabachnick, W. J. & Day, J. F. 2004. West Nile epidemic? These are the questions we will ask. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 4(4): 7-8.
  • Tabachnick, W. J. 2003. West Nile in Florida: The calm before the storm. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 3(1): 11-12.
  • Tabachnick, W. J. 2003. The relationship of West Nile dead birds and human cases. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 3(2): 9-10.
  • Tabachnick, W. J. 2003. Sentinel chicken surveillance programs: Pay attention to safety. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 3(3): 10-12.
  • Tabachnick, W. J. & Day, J. F. 2003. WN in Florida: Detection, surveillance, human cases and Florida's response policy. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 3(5): 10-11.
  • Day, J. F. & Tabachnick, W. J. 2003. Great move by the Indian River County Health Department and the Florida Department of Health, September 2003. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 3(6): 12-14.
  • Tabachnick, W. J. 2002. West Nile virus Detection: The details are important. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 2(2): 7.
  • Tabachnick, W. J. 2002. West Nile virus in North America: Sorting through four years of myths. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 2(5):13-14.
  • Tabachnick, W. J. 2001. A West Nile virus positive bird: WN response by the numbers. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 1(1): 9-10.
  • Tabachnick, W. J. 2001. Florida response levels to West Nile virus detection: Options for mosquito control. BuzzWords, Newsletter of the Florida Mosquito Control Assoc. 1(2): 9.
  • Tabachnick, W. J. & Day, J. F. 2001. Sentinel chicken surveillance and West Nile virus in Florida. BuzzWords, Newsletter of the Florida Mosquito Control Assoc., 1(6): 8-9.

Arboviral surveillance decisions made in response to budget reductions for WNV surveillance will not be easy and will likely result in less useful information to predict and mitigate West Nile outbreaks. Clearly, with all of our hard earned experience with WNV in the U. S., any reduction of arboviral surveillance is a move in the wrong direction. Reducing surveillance options can only serve to reduce the ability of mosquito control and public health professionals to reduce cases and protect the public health and well-being.

Walter J. Tabachnick, Ph.D. - Retired
Florida Medical Entomology Laboratory, Department of Entomology and Nematology
University of Florida/IFAS, Vero Beach, Florida