25 October 2018

The distribution of West Nile virus in the United States

Looks like it should be called West of the Mississippi virus.  The distribution varies from year to year; the map shown is for the most recent dataset (2016).  More info and other maps here.


  1. Being one of the 8-10% of the male population that suffers from colour vision deficiency, what the general population wrongly call colour blindness and what used to be called Daltonism, I thank the makers of this map for their choice of colours.
    Most often the choice of reds, greens, browns, pinks and purples used on maps and graphs, leave me, and I am sure many others with this common condition, with an inability to differentiate between them.
    This had me not scoring as high in school exams and I.Q. tests, simply because with the choice, for instance, between a blue and a green, the answer was impossible to be sure of, and guessing is only right hale the time, less in a multiple choice question.
    Traffic lights were a burden, yes the top one meant stop, but at night with orange street lights (here in New Zealand) in the background, one had to decipher which actual light was the one to look at.
    These days we have L.E.D. traffic lights and for some reason unknown to me, the colours are easy to identify, truly the roads are safer now due to L.E.D.s

  2. I wonder if this largely reflects that Native Americans might be less resistance to this issue?

  3. Hm.. this is showing the number of cases per county? From a quick glance the size (in square miles or kilometers) of the counties west of the Mississippi appear to be substantially larger. Since you say "looks like it should be called West of the Mississippi virus", I would simply note a smaller number of cases might cause more of the map to be colored west of the Mississippi, due to the larger geographical area of western counties. That may be an optical illusion.

    The way to check this would be to look at the number of cases in a tabular form, and compare # of cases west of the Mississippi versus east of the Mississippi or adjust for the size of the counties (such as calculate cases per square area).

  4. And as a follow up, the referenced link (thanks Stan!) has a revised map that is incidence per 100,000 of population. Its VERY different. https://www.cdc.gov/westnile/resources/pdfs/data/WNV-Neuro-Incidence-by-County-Map_1999-2017.pdf

    That shows the most pervasive incidence in a longitudinal band extending down from North Dakota into west/central Texas. So it is most serious west of the Mississippi, but from the previous map the prevalence in the US SW is swamped by that in the longitudinal band.

    Wonder what cases that N-S band of cases? Since its spread by mosquito, I thought it might be related to river and lake systems, but its well west of the Mississippi and not along the Ohio or Missouri river basins, nor in the Columbia basin.


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