SPPI Fact sheet: West Nile Virus in Kansas

By | November 30, 2007

[Illustrations, footnotes and references available in PDF version]



SPPI Fact sheet: West Nile Virus in Kansas

West Nile Virus was introduced to the United States through the port of New York City in the summer of 1999. Since its introduction, it has spread rapidly across the country, reaching the West Coast by 2002 and has now been documented in every state as well as most provinces of Canada. This is not a sign that the U.S. and Canada are progressively warming. Rather, it is a sign that the existing environment is naturally primed for the virus.

The vector for West Nile is mosquitoes; wherever there is a suitable host mosquito population, an outpost for West Nile virus can be established. And it is not just one mosquito species that is involved. Instead, the disease has been isolated in over 40 mosquito species. So the simplistic argument that climate change is allowing West Nile-carrying mosquito species to move into Kansas is simply wrong. The already-resident mosquito populations of Kansas are appropriate hosts for the West Nile virus—as they are in every other state.

Clearly, as is evident from the establishment of West Nile virus in every state in the Union, climate has little, or nothing, to do with its spread. The annual average temperature from the southern part of the United States to the northern part spans a range of more than 40ºF, so clearly the virus exists in vastly different climates. In fact, West Nile virus was introduced in New York City—hardly the warmest portion of the country, —and has spread westward and southward into both warmer and colder and wetter and drier climates. This didn’t happen because climate changes allowed its spread, but because the virus was introduced to a place that was ripe for its existence–basically any location with a resident mosquito population (which describes basically anywhere in the U.S).

West Nile virus now exists in Kansas because the extant climate/ecology of Kansas is one in which the virus can thrive. The reason that it was not found in Kansas in the past was simply because it had not been introduced. Climate change in Kansas, which is demonstrably small compared to the natural variability of the state’s climate history, has absolutely nothing to do with it. A link[1] to the West Nile Virus page of the CDC shows the occurrence of the virus in 2007. At the bottom of the page, can be found links to the occurrence in every year since 1999. By following the progression from 1999 through 2007, one clearly sees that the virus spread from NYC southward and westward, it did not invade slowly from the (warmer) south, as one would have expected if warmer temperatures was the driver.

An article appearing in Science magazine in 2002 nicely summed up the complexity of West Nile and examines its rapid spread–and never once mentions climate change.

Since the disease spreads in a wide range of both temperature and climatic regimes, one could lower the average annual temperature in Kansas by 5 degrees and not make a bit of difference in the aggression of the West Nile virus. Science-challenged claims to the contrary are not only ignorant but also dangerous, serving to distract from real epidemiological diagnosis which allows health officials critical information for protecting Kansas citizens.

A similar false claim by CO2 activists is that warming is responsible for the increased incidents of Lyme disease in the Northeast. However, leading specialists have again found the opposite of activists claims to be true: “Mean temperatures show weak and inconsistent correlations with incidence.”[2] Incidents are instead related to New England farmlands returning to forests near homes, creating “edge habitat” and an explosion in deer populations which carry the blackleg tick. Lyme disease is not a problem in the warmer Southern states.[3]




[2] Effects of Acorn Production and Mouse Abundance on Abundance and Borrelia burgdorferi Infection

Prevalence of Nymphal Ixodes scapularis Ticks

Richard S. Ostfeld, Eric M. Schauber, Charles D. Canham, Felicia Keesing, Clive G. Jones, Jerry O. Wolff

Vector-Borne and Zoonotic Diseases. Mar 2001, Vol. 1, No. 1: 55-63

Also: http://www.hsph.harvard.edu/review/nantucket_fever.shtml