West Nile Virus


Tracking West Nile Virus with GIS

Introduction to Geospatial Analysis

Zac Andereck, Dustin Ross, Amy Uttinger, Kyle Morris


Table of Contents
Introduction West Nile Virus
GIS Implementation Conclusions


The appearance and rapid migration of West Nile Virus in the United States has allowed a new role in GIS to emerge. The use of GIS software allows state and national health organizations to track the spread of the disease. It also allows for precision based preventative applications to be administered in combating the spread of the disease.

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West Nile Virus

West Nile Virus was first discovered in 1937 in the West Nile region of Uganda, in eastern Africa. It is unknown specifically when the virus first migrated to the United States, but it was first officially identified in 1999 in the Queens borough of New York City. It was blamed on the milder than normal winter weather that allowed the survival of mosquito larvae throughout the season (NASA, 2002). That year it caused 62 cases of encephalitis and 7 deaths. Since then the virus has spread throughout most of the lower 48 states. As of November 30th, 2004, 45 states have a confirmed case of West Nile Virus in either a bird, horse, or human.

West Nile Virus is a flavivirus that is transmitted through the bite of an infected mosquito. It can infect birds, horses, humans and a few other mammals. The symptoms of West Nile Virus in an infected person fall into two categories. The mild form of the disease is usually referred to as West Nile Fever. The symptoms include fever, headache, back pain, muscle aches, lack of appetite, vomiting, abdominal pain, sore throat, nausea and diarrhea. These symptoms usually last between 3-6 days, though have been known to last longer.

The more severe form of the disease is called West Nile Encephalitis. According to the CDC, this form of West Nile Virus is called "a "neuroinvasive disease" because it affects a personís nervous system. Specific types of this neuroinvasive disease include: West Nile encephalitis, West Nile meningitis or West Nile meningoencephalitis. Encephalitis refers to an inflammation of the brain, meningitis is an inflammation of the membrane around the brain and the spinal cord, and meningoencephalitis refers to inflammation of the brain and the membrane surrounding it (CDC, 2004)." This form requires immediate medical attention and hospitalization. It is the most deadly form of the disease.

In Kansas, there are five main species of mosquitoes that transmit the disease. The species are Culex pipiens, Culex restuans, Culex salinarius, Culex tarsalis, and Culex erraticus.

Culex pipiens and Culex restuans prefer to bite or feed on birds, but if their breeding sites are close to homes they might bite people and domestic animals.† Both species breed in standing water, especially water polluted with organic matter.† They are weak fliers and are most active at dawn and dusk.

Culex salinarius feeds indiscriminately on birds and mammals, including humans.† It is found in fresh and saltwater marshes, lakes, ponds, and man-made containers around homes.† It is a good flier and active from sunset to sunrise.

Culex tarsalis is one of the most abundant mosquitoes in Kansas.† It breeds primarily in rural areas in temporary to semi-permanent depressions in pastures, ditches and springs.† It is a good flier, is most active at dusk, and feeds most frequently on cattle, chickens and people.† In addition to being a vector of West Nile Virus, this mosquito is the main vector of western equine encepahalitis.

Culex erraticus is present in forested areas.†It is a weak flier and feeds on forest animals (K-State Research and Extension, 2004).

Kansas reported its first case of West Nile Virus in 2002. Since 2002 there have been over 140 confirmed cases of West Nile Virus in humans with 10 individuals dying from the disease.

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GIS Implementation

GIS has been implemented into both state and national health and science services to track, monitor and develop ways to slow the spread of West Nile Virus. The following maps were created in ArcView 3.3 to show the number of reported human cases and deaths associated with West Nile Virus in both 2003 and 2004. The images were created by creating a database from information obtained at the CDC website and then entered into ArcView 3.3. The resulting maps were exported to jpeg format for use in the webpage.

Number of reported human cases in the United States in 2003.

(Source CDC, 2004)

Number of reported human cases as of November 30th, 2004.

(Source CDC, 2004)

Deaths attributed to West Nile Virus in 2003.

(Source CDC, 2004)

Deaths attributed to West Nile Virus as of November 30th, 2004.

(Source CDC, 2004)

This simple, but effective, method shows that the numbers of reported cases and deaths associated with West Nile has fluctuated in the southwest United States, but has declined some in the northeast and central United States. One reason for this decline is the implementation of GIS initiative programs at the local, state, and national level.

On the national level, NASA, in 2002, developed the Public Health Applications Program to use its cutting edge technology to help combat the disease. The center hopes to stop the transmission of this disease by research methods involving Earth Observing Systems, to identify environmental indicators relevant to West Nile Virus (NASA, 2002). One such approach is using the Earth Orbiting satellites to track the movement of key mosquito species and their favorable habitats. The images below show the species Culex pipiens, Culex restuans, and Culex salinarius, and thier extent in the United States. Notice that Kansas is covered completely by these species.

Extent of the mosquito species Culex pipiens.

(NASA, 2002)

Extent of the mosquito species Culex restuans.

(NASA, 2002)

Extent of the mosquito species Culex salinarius.

(NASA, 2002)

  At the state level, the Monterey County Health Department, California, addressed the West Nile Virus problem in their area by retaining a grant from NASA in 2003 to conduct a research project identifying mosquito habitats that can transmit West Nile Virus (Anderson, 2004). The first phase of the project entailed the creation of vector maps and the second was the implementation of a dynamic Geographic Information System to track virus incidents (Anderson, 2004). High risk areas were identified by mapping the breeding source and adult habitat areas of the disease carriers in correlation with the county population.

Vector maps were developed depicting mosquito breeding source area, adult mosquito habitat areas and high-risk mosquito source and habitat areas (Anderson, 2004).

Vector map developed by the Monterey County Health Department.

(Anderson, 2004)

Based on information acquired, the department was able to identify the three mosquito species most likely to carry the virus. Darryl Tyler, GIS Analyst for the Monterey County IT Department, stated that this project helped decision-makers to understand that remote sensing technology is a highly-effective tool for assessing current and future diseases and can provide so much more than just nice photos (Anderson, 2004).

Most other states have some sort of GIS initiative to help monitor and combat the disease. The CDC has a website that lists all of the states that have a plan in place.

At the local level, Richland County, South Carolina, Bradshaw Consulting Services applied GIS technology to mosquito control practices to show local county officials that money could be saved in their efforts against the pest. They first applied GIS to the control of mosquitoes in the summer of 2000. When West Nile Virus was identified in the county, Bradshaw Consulting worked with the local health officials to develop a way to warn and inform the citizens of the county.

Bradshaw Consulting used ArcView software to develop a computerized interactive map that included all of the county roads, mosquito breeding sites, population density, rainfall, temperature and census boundaries. These interactive maps were uploaded into GPS enabled handhelds that were used in the field collect more data. When the data is collected it is brought back the office and downloaded into a desktop computer for analysis. An action plan is then developed for the region in which the data was collected and specific treatments can then be applied to combat the problem. What used to take the company months to do, now takes a matter of minutes to know where the mosquitoes are located and how to effectively treat the area. It cuts down on paperwork, labor costs, and data collection costs, and hopefully the number of people infected by this disease (Wilson, 2004).

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GIS can be used effectively to help track, monitor and combat the spread of a disease, not just West Nile Virus. As the organizations mentioned above, the use of a GIS package can help the local, state, and national level organizations develop a comprehensive plan to keep the disease in check. The continual monitoring of the disease will also keep the public informed of the disease and how to protect the population from having a serious epidemic.

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NASA, Goddard Space Flight Center, October 8, 2002. NASA Researchers Developing Tools To Help Track And Predict West Nile Virus, 3pp. Website.

Anderson, Ian, May 28, 2004. Directions Magazine, Combating West Nile Virus With Remote Sensing, 2pp. Website.

Center For Disease Control West Nile Virus Website.

Kansas Department of Health and Environment West Nile Virus Website.

Kansas State Research and Extension Website.

Wilson, Joey., 2004 Battlers Buzzing about GIS Technology, Bradshaw Consutling Services Website

Webpage completed for EB/ES 351: Introduction To Geospatial Analysis
© Z.D. Andereck (Dec. 2004)

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