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Better Keep Pesticides In the last few decades, pesticide use has increasingly been scrutinized in this country, with some segments of the population demanding elimination of most uses of the substances. However, it is important to realize that pesticides serve a valuable function in society in preventing/controlling infectious diseases carried by insects and other arthropods. They are in effect--powerful public health tools. Pesticides are substances intended to prevent, destroy, or repel pests. Although most are synthetic chemicals, some are plant derivatives, inorganic dusts, or biological agents/products such as bacteria or their toxins. The term "pesticide" is usually further subdivided into more specific terms such as: fungicide (kills fungus), herbicide (kills plants), acaricide (kills mites and ticks), avicide (kills birds), etc. Emerging or Re-emerging Vector-borne Diseases Vectors are insects, mites, ticks, etc. that can transfer a disease agent from one host or place to another. Accordingly, vector-borne diseases are those carried by bugs. Many vector-borne diseases are emerging ("new" diseases) or re-emerging, including Malaria, Lyme disease, dengue, ehrlichiosis, Rift Valley fever, and West Nile virus. For example, malaria--the number one vector-borne disease worldwide--continues to worsen in many areas. (See ACSH's press release about how DDT could help fight malaria if it weren't banned.) There are now an estimated 300-500 million cases of malaria worldwide each year with 2-4 million deaths. Since 1975, the mosquito-carried disease, dengue fever, has surfaced in huge outbreaks in more than 100 countries. Some experts estimate that there may be as many as 100 million cases of dengue each year. It is called "break-bone fever" because you feel like all your bones are breaking. The flea-transmitted disease, plague, is reemerging. A definite trend has occurred worldwide since 1981: an increase in the annual number of cases to nearly 3,000 per year, and an increase in the proportion of cases reported in the African region. In the U.S., cases have traditionally occurred out west, but lately, there has been an increasing number of states reporting cases and an eastward movement in human case occurrence. The parasitic disease, leishmaniasis, carried by sandflies, is increasing as well. Visceral, cutaneous, and muco-cutaneous forms of the disease occur. But perhaps the worst is muco-cutaneous wherein much of the face erodes away, leaving the patient hideously disfigured. The incidence of cutaneous leishmaniasis is on the rise in Central and South America because of road building, mining, oil exploration, deforestation, and establishment of communities adjacent to primary forest. Once thought to be absent from the U.S., visceral leishmaniasis may now be established here. A recent article reported more than 1,000 hunting dogs infected with the disease from twenty-one U.S. states and Ontario, Canada. Lyme disease, almost unheard of in 1979, is now the number one tick-borne disease in the U.S. with approximately 17,000 cases reported each year. Other tick-borne diseases such as babesiosis and ehrlichiosis are also emerging. Several new Babesia species infecting humans have been found. Likewise, there are three Ehrlichia species in the U.S. that produce spotted-fever like illnesses, clinically similar to the tick-borne Rocky Mountain Spotted Fever. Others will likely be found. All of these new or emerging infectious diseases have raised considerable concern in the medical community about the possibility of widespread and possibly devastating disease epidemics. Cause for Future Concern Changes in society such as population increases, ecological and environmental changes, and especially suburbanization (building homes in tracts of forested lands) are contributing to an increase in incidence of many of these vector-borne diseases. It appears that we are in a precarious situation. The entire ecosystem--including plant and animal life on earth--is being affected by humans. People once lived in far-removed, relatively isolated groups. Now we are all essentially one large community. Further, things such as population increases, building cities in/near jungles, and widespread and frequent air travel are creating the opportunity for a great plague. For example, one study showed that the number of international departures from U.S. airports doubled from 20 million to nearly 40 million between 1983 and 1995. A person on safari in the African jungles today might be in New York City tomorrow--maybe sitting by you at the dentist office! What strange disease did they bring back? Should one or more new "emerging" vector-borne diseases begin to spread, control of the epidemic would be difficult. If the disease agent is a virus, specific treatments are unavailable. The only way to stop a viral vector-borne illness is to kill the vectors, reducing them to a low enough level to interrupt virus transmission. If the vector is a flying insect, control of an epidemic is even harder. Compounding all of this, insect species are sometimes resistant to many of the insecticides used to control them. The Need for Pesticides Pesticides are highly active biological compounds (but no more so than prescription drugs, which are consumed by the millions of pounds every day). LetÕs face it--pesticides are poisons, designed to kill things. But the EPA registration process, requiring many years of product testing and review, helps ensure that EPA-registered products are safe when used according to their label directions. Millions of dollars are invested in testing pesticide products--before they ever reach the consumer--for their relative safety to humans and the environment. Prospective pesticides are tested for harmful effects to adults, children, the unborn, as well as the environment. Some people claim that pesticides are destroying the environment and causing widespread disease (such as cancer) in the human population. But where is the evidence? Wildlife is rebounding after years of decline. There are more deer and wild turkeys in the U.S. now than at the turn of the century. Raptors are back. People are healthier and living longer. Overall cancer incidence rates are decreasing (although there are a few specific categories with increases, mostly related to smoking). We must be doing something right. Pesticides are important public health tools. In addition, they are "environmental medicines" to correct insect imbalances. I personally have been in places where--for example--ticks were literally running up my legs by the hundreds and/or mosquitoes were landing on me at rates greater than 200 per minute. No amount of "home remedies" or "natural control" products would have helped me in those situations. Sometimes we need traditional, synthetic pesticides. And we need a wide array of the products to combat any vector-borne diseases that may arise, or any re-emergence of existing diseases. Certainly, integrated pest management and other strategies to reduce pesticide use are in order, but in many cases insect populations explode and are unmanageable by non-chemical methods. We must have pesticides readily available for use. Not only do we need pesticides, we need them with all kinds of labeled (allowed) uses. Registrations for many pesticide uses are considered "minor" by the EPA and chemical companies and thus not much attention is paid to them. In fact, many of these potentially useful minor uses are being dropped totally. Even though a "public health" use may be allowed by the EPA for a particular pesticide, the pesticide may not be available if the company decides (due to EPA review or anti-pesticide group harassment) to quit making it. This concerns me, and it should concern us all. We need all legitimate pesticide registrations to remain in effect, giving us a repertoire of weapons against insect pests. I'm not sure what the future holds, but I think it's safe to say that there will continue to be increased human population numbers, plenty of infectious diseases (both old and new), and widespread, frequent international travel. To me, this is a combination bound to lead to disease outbreaks. We'd better keep our pesticides. Jerome Goddard, Ph.D., is Clinical Assistant Professor of Preventive Medicine at University of Mississippi Medical School in Jackson, MS. |
