by S. Todd Stolp MD
©June 2004
The success of a species on earth is a product of a balance between the forces that act to keep the organism confined and the capability of the organism to successfully disseminate. Whether we are considering the magnificent simplicity of the helicopter wings attached to each seed of a pine cone, or the complex migration of sea turtles, this principle is the ultimate determinant of whether an organism will expand it’s territory of influence. The same rules govern the ability of viruses and microbes to continue their invisible cohabitation with their hosts. To control human disease it is appropriate to remain cognizant of our most effective weapons in keeping certain infectious agents, such as the West Nile Virus (WNV), at bay. It is also well to respect the strengths of our foes in addition to our own weaknesses.
The relentless spread of WNV to California has made ingenious use of the migratory bird population as a mass transit system. While members of the Corvid family (Ravens, Crows, Jays and Magpies) frequently succumb to infection with this virus, other birds often suffer little other than a headache. Infected members of the wild bird population provide a source of the virus to be easily picked up by a mosquito and then transmitted to unsuspecting animals at the next mosquito meal. It is testimony to the intimate relationship that we have with other creatures on this planet to realize that the over 9000 people in the U.S. who were diagnosed with West Nile Virus infections last year were bitten by mosquitoes which had also sipped the blood of a bird or two.
To our credit, birds and other animals have developed a formidable internal police force to keep watch against such devious invading microbes. Through research devoted to understanding the Human Immunodeficiency Virus, we have increased our respect for the tremendous protection afforded to us by our immune systems. We have taken advantage of that protection by developing vaccination programs that have effectively rendered infections such as smallpox, measles, polio, and pertussis impotent. Unfortunately, it does not appear that a vaccination will be developed in time to be deployed against the West Nile Virus epidemic.
It is also important to recognize that the majority of the 250 U.S. citizens who perished last year as a result of WNV infection were over 50 years of age. This probably reflects a relative weakness of immune system function that occurs with older age.
As we tally our “assets” in preparation for battle against WNV, perhaps none is as valuable as the one which brings humans the greatest pride: intelligence. Each of us should understand that West Nile Virus is incapable of being transmitted by handshake or sneeze. This virus requires the bite of an infectious mosquito in order to do damage. Therefore, if measures are taken to diminish exposure to mosquito bites, the virus will be less successful in causing human misery. Such precautions as wearing long sleeve shirts and other protective clothing, avoiding outdoor activities during dusk, proper use of mosquito repellants containing 15% to 50% DEET (N, N – Diethyl toluamide), repair of torn window screens, elimination of standing water that can act as a breeding ground for mosquitoes, and reporting dead birds to the Health Department are all steps that will help reduce the risk of WNV infection.
While the march of the West Nile Virus across the country has been relentless, and only modestly influenced by vigorous mosquito control programs, and while there is no likelihood that any one person will escape the season free of mosquito bites, there is no substitute for common sense. Prevention of mosquito bites through the measures described by your local health department will go a long way to prevent a personal experience with the WNV epidemic.