Humanitarian Resource Institute:  A U.S. & International Resource on the Scope of Humanitarian Assistance

August 5, 2001

Stephen M. Apatow
Director of Research and Development 
Humanitarian Resource Institute Emerging Infectious Disease Network
Eastern USA: (203) 668-0282   Western USA: (775) 884-4680


In the light of recent human fatalities associated with Eastern Equine Encephalitis virus (EEEV) and presence of West Nile Virus in Northern Florida counties, it is crucial that the potential for an escalation of vector borne disease associated with natural disasters such as floods, tropical storms and hurricanes be evaluated and an appropriate response plan implemented.

According to the guidelines for Arbovirus Surveillance Programs in the United States (

Natural disasters such as floods and hurricanes can create a potential for epidemics of vector-borne disease. When a response to these disasters or emergencies is beyond the capability of state or local governments, the president may determine that a disaster or emergency exists. A presidential disaster declaration makes state and local agencies eligible for reimbursement of disaster-related expenses. The Federal Emergency Management Agency (FEMA), which oversees all federal disaster activities, calls upon CDC to evaluate the risk of vector-borne disease. Reimbursement for vector control depends on the presence of a clear risk of vector-borne disease that can be related to the emergency or disaster.

In order for CDC to rapidly and accurately evaluate the risk of vector-borne disease, it is important for state and local health and vector control agencies to have readily accessible as much data as possible. Historical data should be available for comparison with current data, to show how the disaster is related to any increase in vector or virus activity. The types of information that are needed to estimate the risk of an epidemic are the following:

a) Mosquito population indices (Are vector species present? How do light trap indices compare with previous years and with this year prior to the current disaster?)

b) Virus infection rates in mosquitoes (What is the minimum infection rate (MIR) this year? How does it compare with MIRs in epidemic years? Is virus activity localized or is it widespread?)

c) Evidence of increased virus transmission in vertebrate amplifying hosts (What temporal and spatial patterns are seen and how do they compare with the norm for this locality?)

d) Evidence of disease in equines (WEE/EEE)

e) Rainfall and temperature data (Is there any evidence to show an association between past outbreaks/epidemics and specific weather patterns?)

f) Time of year (Is it relatively early in the virus transmission season for this locality?  activity near populated areas?  Is vector movement between areas of virus activity and populated areas?)

If all of the foregoing information is readily available, a rapid risk assessment can be made using the categories in Table 1. If insufficient information is available, it is necessary to collect at least part of the data before a decision can be made. This frequently delays efforts by state or local agencies to implement the appropriate response. The delay may, in turn, result in increased virus and vector activity and human or equine encephalitis cases.

For additional information, visit the Humanitarian Resource Institute Community & Family Preparedness web site: or Emerging Infectious Disease Network West Nile Virus Reference Library web site:

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