West Nile Virus - The Public Health Role

Courthouse Journal, February 14, 2003
Washington State Association of Counties &
Washington Association of County Officials

Submitted by Dr. Kim Thorburn, Health Officer, Spokane Regional Health District on behalf of Washington State Association of Local Public Health Officials (WSALPHO)

Horse lovers and birders are growing anxious, as our El Nino winter is quickly dissipating into spring. West Nile Virus (WNV) killed at least 2 crows and infected a horse in Washington last fall, signifying its arrival. What that has meant in other places is a disease outbreak: bird die-offs, sick horses and a few cases of human encephalitis. Early spring may mean early mosquitoes and the awakening of WNV.

Counties should be planning now. Mosquitoes that carry the virus have been identified in every Washington county. Human cases will generate intense attention and bird die-offs and sick horses will also create concern. County officials will be looked to for a response.

The goal of the response should be to control the spread of WNV. Mosquitoes, including at least nine species identified in Washington, spread it. Birds are “definitive hosts.” This means that when a carrier mosquito bites a bird (the crow family seems most susceptible), the bird becomes infected. When a mosquito bites an infected bird, it takes in WNV-laden blood and can then spread the virus when it bites another bird or some mammals. We humans and horses are called “accidental” or “dead-end hosts.” That means that we don’t contribute to the life cycle of the virus. Carrier mosquitoes can infect humans and horses but the mosquitoes cannot pick up the virus from us.

Things to consider for a WNV response plan include: clarification of roles and responsibilities (this problem touches many agencies), surveillance, mosquito control (personal protection, habitat control and pesticiding), and public information.

In public health, we have responsibility for surveillance and public information. We have been conducting surveillance for the past couple of years, including mosquito trapping and dead-bird and human encephalitis surveillance. The mosquito trapping contributed to the first Washington State mosquito census in a couple of decades. We were interested in determining if mosquitoes known to carry the WNV reside in Washington. We will now also be turning our attention to looking for virus-laden mosquitoes as a means to track the potential for spread of disease.

Dead-bird surveillance tracks the presence of the virus. Public health officials do not collect dead birds as a means to identify disease outbreaks among birds but rather, use birds as indicators of the presence of the virus. Our focus is human disease and both mosquitoes and birds serve as markers of risk.

While horse owners and birders may be at increased alert with the arrival of WNV in Washington, it is human disease that will predictably generate the most public alarm, especially if we are unprepared with our responses. Most human disease is mild, a flu-like illness, but there are rare instances of encephalitis (brain inflammation), especially among the elderly, and an occasional death. We should anticipate human cases this spring, now that WNV is here in Washington, and upon the diagnosis of human cases, we can also expect demands on public officials to do something.

Public health is prepared to provide information about personal protection (i.e., use of clothing, insecticides and avoidance) and habitat control to prevent mosquito bites. A more challenging pressure on local governmental entities will be calls for mosquito abatement. In jurisdictions with mosquito districts, this issue is easier to deal with than other areas. Lacking a mosquito district, local governments need to consider storm-water drainage, roadside habitats, private property in the hands of owners who are non-compliant about habitat control, and possible referrals to private pest control operators. This means inter-agency cooperation and the time to be meeting is now. We in WSALPHO are prepared to be a resource.