Public Health Benefits Of Pesticides

With new diseases appearing, old diseases reemerging, and environmental and ecological changes occurring, our industry needs every weapon possible to fight this battle.

Infectious diseases are coming back strong after a lull in the years following World War II. The ability of disease germs to adapt to the human defense system and intense pressure from antibiotic use, combined with changes in society, have contributed to this comeback of many infectious diseases.

Also, there are now several "new" diseases, including Legionnaires’ disease, Lyme disease, ehrlichiosis, toxic shock syndrome and Ebola hemorrhagic fever. In just the last four or five years we have seen the appearance of a new strain of bird influenza that attacks humans, a human form of "mad cow" disease and new drug-resistant forms of Staphlococcus aureus. These new or emerging infectious diseases have raised considerable concern in the medical community about the possibility of widespread and possibly devastating disease epidemics.

WHAT WE’RE UP AGAINST. Many of these emerging or reemerging infectious diseases are vector-borne, meaning they are transmitted by insects or other arthropods. Since 1975, 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. The more dangerous forms of the disease, dengue hemorrhagic fever (DHF) and dengue shock syndrome (DSS) with internal bleeding and shock, mainly affect children younger than 15 and about 5 percent of the cases result in death. In the 1970s only nine countries had experienced DHF outbreaks; to date 44 countries have had DHF cases or epidemics.

The malaria situation is worsening as well. There are now an estimated 300 to 500 million cases of malaria each year with 1 to 2 million deaths (mostly children). Several factors are responsible for the resurgence of malaria: 1) insecticide resistance in the vector mosquitoes; 2) drug resistance in the malaria parasite; 3) inadequate funding for malaria control; 4) civil strife with accompanying refugee problems; and 5) increased travel by non-immune expatriates.

For example, 2 to 3 million new cases of malaria have been reported each year recently in Afghanistan as a result of disruption of control, civil disturbance and migration. The flea-transmitted disease, plague, is also reemerging. In the United States, 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 toward the 100th meridian.

The parasitic disease, leishmaniasis, which is carried by sandflies, is increasing as well. 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.

Lyme disease, almost unheard of in 1979, is now the No. 1 tick-borne disease in the United States with about 16,000 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 at least two Ehrlichia species in the United States that produce spotted-fever like illnesses. Others will likely be found.

It could be argued that at least some of this increase in vector-borne disease is due to increased recognition and reporting. Maybe we’re just getting better at making diagnoses. Specific disease recognition is certainly made easier by new laboratory technologies such as polymerase chain reaction (PCR). However, 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.

CAUSE FOR FUTURE CONCERN. 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 providing the opportunity for a great plague. A person hiking in the Amazon jungles today might be in New York City tomorrow and bring back with him or her some new or exotic disease.

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, antibiotics will be of little help in treatment. The only way to stop a viral vector-borne illness is to kill the vectors 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, many insect species are resistant to many of the insecticides used to control them.

THE NEED FOR PESTICIDES. Pesticides are indeed poisons. They are designed to kill things. But the Environmental Protection Agency’s 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 ruining 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 United States now than at the turn of the century. Raptors are back. People are healthier and living longer. We must be doing something right.

In my opinion, pesticides are extremely important to human survival. They are essentially "environmental medicines" to correct insect imbalances. Not only are they needed for crop protection, but as public health tools. We need a wide array of pesticides to combat vector-borne diseases that may arise or any reemergence of existing diseases (such as malaria, dengue, etc.).

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 a wide variety of them with various labeled uses. Even "older" generation pesticides — such as organophosphates (OPs) — are needed. Pesticide resistance is developing to many of the newer synthetic pyrethroid compounds; keeping the OPs gives pest controllers, farmers and vector control personnel another option in managing/preventing insecticide resistance.

Furthermore, registrations for many pesticide uses are considered "minor" by EPA and chemical companies and thus, not much attention is paid to them. In fact, many of these minor uses are being dropped totally. Alternatively, even though a "public health" use may be allowed by the EPA for a particular pesticide, the pesticide is not available if the company decides (due to EPA review or anti-pesticide group harassment) to quit making it. This concerns me. We need all legitimate pesticide registrations to remain in effect as part of our repertoire of weapons against insect pests.

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 air travel. To me, this is a combination bound to lead to disease epidemics.

The author is a medical entomologist for the Mississippi Department of Health and clinical assistant professor of preventive medicine at the University of Mississippi Medical Center, Jackson, Miss. He can be reached at 601/576-7512 or at jgoddard@pctonline.com.