APPENDIX II-AD:  Encephalitis - Fitz

This article is from:


Synthesis/Regeneration 31   (Spring 2003)


Spraying Can Make West Nile Virus Worse!

by Don Fitz, Green Party of St. Louis



It is not entirely correct to say “Spraying has no effect on West Nile Virus (WNV).” There is good reason to believe that spraying can make WNV worse in three ways:

  • Spraying can cause a long-term increase in mosquito populations.
  • Spraying may result in an increased prevalence of WNV in mosquitoes.
  • Spraying can make it more likely that humans will develop encephalitis from WNV.

Most of us learned when we took our first biology course that insects develop resistance to pesticides within a few years. Even if a spray kills 99%, the 1% that survive will pass resistance genes to their offspring. The attempt to overcome the inevitable by using more and deadlier pesticides has come to be known as the “pesticide treadmill.”

Recent facts indicate that pesticide spraying can also increase the mosquito population. Pesticides can kill mosquito predators that have a longer life span than mosquitoes. (See “Belly-Up Goldfish.”)

…spraying may be leading to a higher proportion of mosquitoes carrying WNV.

Less well known is the effect that spraying can have on a “sympatric” species that occupies the same ecological niche. John Howard and Joanne Oliver collected data on spraying the pesticide naled near New York’s Cicero and Toad Harbor Swamps for mosquitoes which carry eastern equine encephalitis (EEE). Though there were short-term reductions after sprayings, from 1984 to 1994 there was a 15-fold increase in the number of mosquitoes. The researchers also discovered a large decrease in a different species of mosquitoes living in the same area. When the populations of non-EEE carrying mosquitoes were killed off, the EEE-carrying mosquitoes took their place. The authors concluded that the increase in disease-spreading mosquitoes “discredits the rationale that preventive applications of naled reduce the risk of EEE.”

A major cause of growth in mosquito-borne diseases is global warming and the real solution is massive reduction of greenhouse gases. The cover article in the August, 2000 Scientific American by Harvard Medical School’s Paul Epstein predicts that global warming will lead to large growth of mosquito-borne diseases such as malaria, dengue fever, yellow fever and several kinds of encephalitis. He explains that warmer weather creates more breeding grounds, lengthens the time of year that mosquitoes are active, allows them to “proliferate faster and bite more,” and speeds up the rate of viral reproduction inside the mosquitoes. Spraying pesticides while ignoring global warming is like being on an airplane heading towards a collision, and, instead of changing the plane’s course, telling people they should walk to the back of the plane so they will be “doing something” to be further away from doomsday.

In addition to increasing mosquito populations, spraying may be leading to a higher proportion of mosquitoes carrying WNV. Richard Pressinger, of, theorizes that massive pesticide spraying could cause genetic problems which would increase the proportion of mosquitoes which develop encephalitis when they bite an infected animal. He hypothesizes that mosquitoes hit with a sub-lethal dose of pesticide could be damaged genetically so that their offspring have defective stomach linings. The malfunctioning of the stomach lining could result in the virus being more likely to move into the salivary gland and pass into a bitten human.

Pesticides are known to weaken the immune systems of mammals (including humans), rendering them less able to ward off diseases such as encephalitis. This is one of the listed concerns with permethrin. Thus, the spray we are told will “protect” us from mosquitoes may actually damage our immune systems, making us more vulnerable to the disease.

…the most important preventive action is to stop spraying pesticides.

Dr. Dennis Goode, of the Biology Department at the University of Maryland, believes that the pesticides currently being used could also make it more likely that WNV would be transformed from a mild flu to a serious encephalitis. For encephalitis to occur, the virus must cross the blood-brain barrier. Pyrethroids are among the agents that impair the blood-brain barrier. Pyrethroids are the basis of the pesticides being used in 2002. Additionally, piperonyl butoxide (PBO), which is a synergist added to increase the killing power of the pesticide, works to prevent pyrethroids from breaking down, lengthening the period of time the pesticide works to weaken the blood-brain barrier.

While some of the theories described here are substantiated and others point at processes that could be happening, the body of research as a whole indicates that spraying pesticides for WNV is the worst possible thing to do. We have good reason to suspect that spraying will increase mosquito populations and that the increased populations will have a higher proportion carrying WNV and be more pesticide resistant. Simultaneously, spraying could make humans both more likely to catch a mild version of WNV and transform if from a mild flu to a serious encephalitis. If someone asks, “What can we do to stop the spread of WNV” the answer should be that the most important preventive action is to stop spraying pesticides. Spraying to fight WNV is like trying to put out a fire by pouring gasoline on it.

[21 apr 03]

Synthesis/Regeneration home page | s/r 31 Contents