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West Nile Virus Poses Physical, Economic Threat

by Wyoming Livestock Roundup

Since 2002 when the first human case was reported, West Nile virus has found its way throughout all corners of Wyoming, impacting multiple facets of agriculture, wildlife and human health. The physical and economic toll on the residents is not immaterial when you look at the Department of Health’s cumulative data for the state at In the past 12 years, over 700 Wyoming residents have contracted the virus with 17 of those cases being fatal. 

For some, contracting the virus is similar to getting the flu, with symptoms such as fever, headaches, fatigue and back pain. Nationally, it is estimated that 99 percent of the total reported cases are of this mild fever variety. The other one percent represents individuals that develop serious neurologic illnesses such as encephalitis or meningitis. These extreme cases of infection can lead to long-term health impacts or possibly death. 

By now, many Wyoming residents know someone who was exposed to the virus and had to deal with the physical impacts, especially in Fremont, Goshen, Campbell and Platte counties, which have the four highest reported cases in the state.


The impacts from West Nile virus extend beyond physical health into economical. 

In 2002, Louisiana experienced 329 West Nile virus human cases with an estimated economic cost of $20 million dollars (Zohrabian A. West Nile virus economic impact, Louisiana, 2002 Emerg Infect Dis. 2004 Oct;10(10):1736-44). This cost was based on lost wages, health care costs and epidemic management costs. 

In 2005 researchers estimated an outbreak in Sacramento County, Calif. of 163 reported cases had an economic impact of $2.28 million dollars using a similar formula as Louisiana (Barber L. Economic Cost Analysis of West Nile Virus Outbreak, Sacramento County, California, USA, 2005. Emerg Infect Dis. 2010 Mar.). 

Comparing the entire state of Wyoming to Louisiana, or a single county in California, may seem disproportionate, but in 2013 Sacramento County, with a population of 1.355 million residents, only reported 10 West Nile virus human cases where Wyoming, with a population of 576,412, reported 40. 

Closer to home

When relating Wyoming’s reported West Nile virus incidents to the formula used in both Louisiana and Sacramento County, the state’s 12-year economic impact is $20,701,900, without considering the additional impacts to livestock and wildlife.

This figure could be exponentially higher if not for the West Nile virus management programs implemented throughout the state. The agencies managing these programs vary locally but include Weed and Pest Control Districts, municipal vector control programs and, in several cases, county health departments. 

A majority of these programs utilize Emergency Insect Management grants through the Wyoming Department of Agriculture for financial assistance. The Emergency Insect Management program has also played a key role in the state’s grasshopper management and the Black Hills pine beetle mitigation programs. 

In 2013, the program provided $1.3 million statewide to assist with West Nile virus programs. This was matched with $3.2 million of local funds.


Gauging the success of a vector control program is difficult due to an inability to accurately account for all individuals protected by the program. 

For Sacramento County during the 2005 epidemic, conditions allowed researchers to compare the cost of emergency aerial spraying to the cost of complacency and determined spraying was cost effective if they prevented a minimum of 15 cases of West Nile virus. 

In Wyoming, we gauge program success through monitoring protocols as required by the Emergency Insect Management grant. These protocols require participating programs to identify and monitor Culex tarsalis mosquito populations, the primary vector of West Nile virus in Wyoming, and compare trapping levels pre and post treatment. The protocols were developed by the University of Wyoming, and annually, they provide training on how to implement them. 

Although the protocols may not calculate a “cost-benefit” comparable to the Sacramento County study, they do provide an accurate picture of local program success. By using these protocols many vector management programs in the state have adapted their treatment timings to correlate with peak Culex tarsalis activity. 

Many of the local programs can demonstrate a 95 percent or better control of vector mosquito levels during peak seasonal activity.


It’s safe to say West Nile virus still poses a significant threat for Wyoming in 2014. This past year, along with many of our neighboring states, Wyoming experienced some of the highest per capita rates of West Nile virus neurological infections, according to data from, which leads many of us to believe, with enough moisture and hot days, this summer won’t be much different. 

With time, we may see a decrease in human incidents due to an immunity build-up or even the introduction of a human vaccine. Until then protecting yourself by wearing long-sleeved shirts and pants and using DEET based repellents should be a common practice during the summer when mosquito activity is at its highest.

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