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Center of Excellence for Emerging and Zoonotic Animal Diseases

Pathogen of the Month



August pathogen of the month:

West Nile Virus


What is it and how widespread is it? West Nile virus is the most common mosquito-borne disease in Kansas and the United States. Several species of mosquitoes are responsible for transmission of arboviruses, but Culex species are the primary vector for West Nile virus in the United States.

What is its history? The World Health Organization says that West Nile Virus was first isolated in a woman in the West Nile district of Uganda in 1937. It was identified in birds in the Nile delta region in 1953. Human infections attributable to WNV have been reported in many countries around the world for over 50 years.

In 1999 a West Nile Virus strain circulating in Israel and Tunisia was imported in New York, producing a large and dramatic outbreak that spread throughout the USA in the following years. The outbreak highlighted that importation and establishment of vector-borne pathogens outside their current habitat represent a serious danger to the world.

How does the infection spread? The Centers for Disease Control says mosquitoes become infected when they feed on infected birds. Infected mosquitoes then spread West Nile virus to people and other animals by biting them with horses being the most susceptible. In a very small number of cases, West Nile virus has been spread through such means as exposure in a laboratory setting, blood transfusion or organ donation.

What are the symptoms? Most people do not develop symptoms. Only about 1 in 5 infected persons do develop symptoms, generally a fever


(red indicates high level of risk; yellow indicates moderate level of risk.)

accompanied by headaches, body aches, joint pains, vomiting, diarrhea or rash. While people usually recover quickly, it is possible for fatigue to last for weeks or even months.

Are there treatments or vaccines? There is no vaccine to prevent West Nile Virus in humans.  There are approved vaccines for use in horses. The CDC recommends use of over-the-counter pain relievers to reduce fever or relieve other symptoms. In severe cases, hospitalization may be necessary.

Are there current outbreaks? The Kansas Department has identified about 70 Kansas counties – essentially the eastern two-thirds of the state – as at high risk for West Nile Virus. That is largely due to this summer’s heavy rains, which have increased the number of breeding areas for mosquitoes. That is coupled by normal rising summer temperatures, which shortens the time required for mosquitoes to mature to biting adults. It should be noted, however, that as of mid-July no confirmed cases of West Nile Virus had been reported.



Sources: Centers for Disease Control, CEEZAD staff