Insect-Borne Diseases and Global Warming

Reader Contribution by Richard Hilderman and Ph.D.
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Image by Susanne Jutzeler, suju-foto from Pixabay 

As reported by the Center for Disease Control and Prevention, 2012 has set a record for the number West Nile virus infections 2,118 ill and 92 dead.  The geographic reach is broad there are cases in 44 states.  The problem is going to get worse!  Health officials expect this mosquito-borne disease to continue to peak into September and early October. The West Nile virus lives in birds and mosquitos bite infected birds.  The mosquito acts as an intermediary host where the virus reproduces and the mosquito passes the virus to humans when it feeds on them.  Is there a relationship between insect-borne diseases and global warming? 

The best insecticide against insects is cold weather.  Nine of the 10 hottest years on record occurred between 2002 and 2011 with 2012 likely becoming the hottest year ever recorded!   We are having earlier springs and hotter summers which mean mosquitos can breed earlier and longer.  

Global warming produces severe weather events such as massive floods.  After the storm passes the water recedes but leaves small ponds, pools and puddles.  This stagnant water becomes an optimum breeding ground for mosquitos.   

Global warming has also increased the geographical range that mosquitos can act as an intermediary host for viruses.  The mosquito has a short life span and is cold blooded.  In the past insect-borne viral diseases were not found frequently in northern latitudes because the cold temperature slowed down the viral reproduction and the mosquitos died before the virus became infectious to humans.  However, global warming is allowing viruses to reproduce faster in northern latitudes and thus mosquitos can transmit infections to humans in a wider geographical range.  All this means more mosquitos biting more people and animals in more places around the globe, resulting in more cases of insect-borne diseases. 

As we continue to pump more and more carbon dioxide into the atmosphere (90 million tons per day) the global temperature will start rising at a much faster rate due to positive feedback loops.  This will trigger an increase in not only West Nile virus infections but also other insect-borne viral infections such as yellow fever and dengue fever.  This is already happening!  El Salvador reported 22,000 cases of dengue fever in 2008, 20 times more than the number in 2003. 

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