Insect-borne diseases

The use of economic poisons has expanded in the field of public health since their indispensability has been shown in the control of insect-borne diseases. The organic insecticides, especially DDT, are now being used extensively in the control of malaria, yellow fever, dysentery, and other diseases. Their use in this field will certainly expand for years to come. 

The time-honored method of controlling insect-borne virus diseases is by breeding resistant varieties. This has been practical in annual crops, but is hopelessly slow in tree crops, where it may take 20 years or more to test a new variety. What is needed desperately is some sort of treatment which will control the virus, probably a systemic treatment, as the virus works within the plant cells. This is not a new idea and work has been done along this line by many workers. A sense of urgency is inevitable, however, when 500 to 600 acres of citrus can be wiped out completely in 3 to 5 years time, followed by an expensive replanting job and a wait of 5 to 6 years to get back into production. This is the outstanding problem at the present time and may need years to answer. 

Chlorinated hydrocarbons One example, DDT, is an insecticide. It was extensively used in World War II to delouse personnel and to prevent the spread of plague and other insect-borne diseases. Today, its use is restricted because of its toxicity and its very long life. Even though DDT is extremely effective, it is difficult to eliminate in nature. Its restricted use in some third-world countries has resulted in large increases in deaths due to malaria and other insect-borne diseases. 

Structure of DDT. DDT is DichloroDiphenylTrichloroethane, or l,l,l-trichloro-2,2-bis-(/ -chlorophenyl)ethane. DDT was the first chlorinated insecticide. Its use rendered large parts of the world safe from insect-borne disease and starvation, but it has accumulated in the environment. 

Alkyl halides have contributed to human health through their use as insecticides. Since antiquity, people have died from famine and disease caused or carried by mosquitoes, fleas, lice, and other vermin. The black death of the Middle Ages wiped out nearly a third of the population of Europe through infection by the flea-borne bubonic plague. Whole regions of Africa and tropical America were uninhabited and unexplored because people could not survive insect-borne diseases such as malaria, yellow fever, and sleeping sickness. 

As shown in Table 1.2, many diseases can be transmitted to humans by insects, ticks, or mites. It has been documented by the World Health Organization (WHO) and in other reports that the use of synthetic insecticides can markedly reduce the risk of insect-borne... 

Insect repellents containing DEET have become particularly popular because of the recent spread of many insect-borne diseases such as West Nile virus and Lyme disease. DEET does not kill insects—it repels them. It is thought that DEET somehow confuses insects so that they can no longer sense the warm moist air that surrounds a human body. 

For this discovery of DDT s potent toxic effects on insects, he received the Nobel Prize for physiology or medicine. However, DDT proved to be a two-edged sword. With its chemical derivatives, DDT became the most widely used insecticide for more than 20 years and was a major factor in increased world food production and suppression of insect-borne diseases, but... 

A report on Emerging Infections prepared for the American Institute of Medicine poinis out that although insect-borne infections were more or less controlled in North America and Europe by the mid-1970s, they could return. Malaria is one example since the vectors remain and the health authorities are now less vigilant in controlling the disease. 

Table 18,1. A global summary of the major insect-borne diseases...

Dichloro-diphenyl-trichloroethane, or DDT, came to the attention of the U.S. army because, fighting a war in Africa and the South Pacific, there was a need to kill malaria-carrying mosquitoes. The nation s scientific capabilities had been mobilized for the war effort, and the task of controlling insect-borne diseases was assigned to the Agriculture Department s entomology laboratory in Orlando, Florida. The Orlando scientists recognized that war conditions required different approaches than peacetime solutions should be quick, rather than optimal, and they should be usable worldwide rather than tailored to local conditions.15... 

Who are these new adversaries They are led by viruses such as the human immunodeficiency virus (HIV) which causes AIDS, the hanta viruses, herpes, and the emerging viruses such as Ebola and Lassa fever. They are bacteria, such as Salmonella, Staphylococcus and Mycobacterium tuberculosis, that once were easily killed by a host of antibiotics and are now resistant to most drugs we develop. They are the insect-borne diseases such as Lyme s, Dengue, and West Nile. They are the prions, a lifeform less complex than viruses that can only survive in a host and cause debilitating, and presently noncurable, madness in animals and humans. They are the insects themselves that are resistant to many organic pesticides and which continue to cause destruction of plant life. Why are these threats emerging now ... 

The efficiency of DDT against insects was demonstrated experimentally in 1942, and it was successfully applied to combat insect-borne diseases of soldiers, like malaria, carried by mosquitos, in thejungles of the Asian region and the Pacific islands during World War 11. After the war, this preparation was used worldwide, since ... 

From 1945 to 1950 after World War II, Japan experienced very poor sanitary conditions due to the destruction caused by the war. Various kinds of infectious diseases were prevalent. In order to control the vector arthropods of insect-borne diseases, about 4 million Tokyo citizens were treated with DDT. Indeed, DDT saved the lives of many Japanese people after World War II. 

The environmental health business focuses on developing products that promote a safe and comfortable living environment (see Figure 4). One of the primary roles is offering measures to protect people from insect-borne infectious diseases, such as malaria and dengue fever. OQier important roles are offering... 

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