Central  South  Dakota  Medical News
The Clinical View
by Phillip Hoffsten,M.D.30 June 2004

AVOIDING MOSQUITO BITES

      In medical terms, a vector is an insect or animal that transmits an infection from one source into someone who will be infected.  The most effective vector is this world for humans is the mosquito.  It carries more than 100 different possible viruses in addition to various parasites, including malaria.  Five years ago in 1999, a virus called “West Nile Virus” was introduced into the East Coast of the United States.  In the five years since then, this virus has spread across the country now reaching the west coast.  Estimates for South Dakota this year indicate there will probably be at least as many or slightly more cases of West Nile Virus as compared to last year.

     West Nile Virus is carried by mosquitoes which are the vector carrying the virus from birds which is the natural reservoir for the West Nile Virus.  Mosquitoes bite the birds and thereby acquire the virus.  When the mosquito subsequently bites horses or cattle or hogs or people, the disease can be transmitted on to these other species.  Unfortunately, there is no meaningful treatment for the condition other than supportive measures until the virus disease runs its course.  The disease is characterized by headache, diffuse muscle aching, high fevers, and disruption of the gastrointestinal tract with nausea, vomiting and diarrhea.

     The only meaningful way to deal with West Nile Virus is to avoid getting bitten by mosquitoes.  Practical measures to avoid mosquito bites include:

     1.  Wearing  protective clothing.  For those going into heavily mosquito-infested areas, there are insect repellant permeated clothing that helps repel the mosquitoes.
     2.  Avoidance of outdoor contacts from dusk until dawn.  Mosquitoes are most active in the cool of the evening.
     3.  Bathing frequently.  Mosquitoes are attracted to the very slight amount of ammonia that is produced on human skin.  Thus, given the choice, mosquitoes will choose the
lower limbs and especially the feet as areas to bite.  A cleansing bath before bedtime cuts down the attractiveness of the feet.
     4.  Multiple mail order sources now advertise mosquito attracting and killing machines that one can put in their backyard.  They are advertised as killing thousands of mosquitoes.  Reviewing the medical literature available, I can find nothing that says that these devices are particularly effective.  To me it just makes sense that the more mosquitoes that are killed, the less likely you are to get bitten; but another argument against these devices is that they attract mosquitoes to begin with and don’t kill them all.  If the devices seem to work in your yard, so much the better but I can find no medical information documenting that these devices are effective.

     For many years attempts were made to come up with a repellent that will keep mosquitoes from landing on a person’s skin or biting them if they do land.  I can remember when I was just a child, mom used to put out Citronella candles and then there were various other insect-repellent torches that were put out.  They never seemed to work for me.  Indeed the medical literature does not support the effectiveness of these devices.

     In 1946, the United States Army developed an insect repellant called DEET.  By 1957, it had become commercially available to the general public.  To this day, it is still the most effective insect repellent available.  A lotion formulation of DEET has been shown to have a complete protection against mosquito bites for over 5 hours.  There is virtually no other mosquito repellent that even approaches the effectiveness of DEET, now 45 years on the market.  To be effective, the product needs to be 25-33% DEET.  Lesser concentrations of lotion or spray do not result in adequate coverage to prevent mosquito bites.

     In regard to adverse side effects of DEET, there has been a great deal written.  But after 47 years of use, it appears that the only real adverse effects are those few people who are allergic to the material.  They can develop skin rashes on exposed areas but it does appear that DEET used appropriately is safe for all ages.  It would be recommended it be used for those going out in the evening for reactional activities such as sport events, etc.

     It must be remembered that the only effective way of dealing with West Nile Virus is not to get it.  That means avoiding mosquito bites through the measures outlined above.