A NASA-funded study uses temperature and vegetation data from
satellites to help track and predict where West Nile virus is spreading
in North America. Scientists and public health officials hope one day to
use near real-time maps to focus resources and stave off the disease
This image is a composite of land surface temperatures (LST) recorded between 1997 and
2000 and was used to help monitor and predict the spread of West Nile virus in
the United States.
In the color figure above, the mean land surface temperatures are in red;
annual amplitudeor the difference between low and high annual
temperaturesis in blue; and annual phaseor the timing of annual
temperature peaksappears in green. Brighter colors mean higher values.
The major north-south temperature difference (dull red in the upper part
of the image to bright red in the lower part) is considerably affected
by the Rockies in the west and to a much lesser extent by the
Appalachians in the east. The brighter blue in the upper part of the
image indicates the big difference between highest and lowest
temperatures during the course of a year at higher latitudes.
There is less variation in the timing of the annual
peak of land surface temperatures, which occurs earlier in the south than in the north.
Black dots superimposed on this image are the locations (county
geo-centers) where birds infected with West Nile virus were reported
between January and October 2001.
Scientists working with the International Research Partnership for
Infectious Diseases (INTREPID) program based at NASA are using such
imagery to define and predict the conditions where mosquitoes transmit
West Nile virus in the U.S.
The conclusion reached about the importance of any single variable depends both upon
its value and context. A temperature of 30°
Celsius (86° Fahrenheit) might be fatal for a mosquito at low humidity
but survivable at higher humidities. The work done here on West Nile
virus and other diseases shows very clearly that it is a unique
combination of temperature, humidity, and vegetation variables that tends
to determine mosquito and disease presence and abundance.