C. INSECTS CARRY DISEASE Many of the diseases which are prevalent in the less-developed areas and which have, in fact, inhibited the development of the countries involved, are transmitted by various species of arthropods, including mosquitoes, fleas, lice, ticks, mites, and various species of flies. When one considers such diseases as malaria, yellow fever, filariasis, plague, endemic and epidemic typhus, kala-azar, bacillary dysentery, sleeping sickness, trachoma, and others, the control of insects assumes major importance in international health programs. The method of transmission by arthropods varies tremendously with the different diseases. In some cases, purely mechanical transmission of pathogenic organisms on the feet or mouthparts of the insect occurs, such as in bacillary dysentery and cholera carried by flies. In others, there is a complex relationship in which the insect is necessary in the life cycle of the disease agent-malaria, yellow fever, and filariasis in mosquitoes, sleeping sickness in tsetse flies, and others. The control of each insect-transmitted disease presents a separate problem based upon a complete knowledge of the arthropod and the disease agent. In many cases, this imposes a heavy burden of expense on many of the poorer countries where the need for specific knowledge and efficient application is greatest. D. EXTENT OF THE MALARIA PROBLEM Malaria is a chronic, debilitating disease transmitted by species of the Anopheles mosquito. It is estimated that at least 250 million people annually suffer clinical attacks of malaria and that each year perhaps 2.5 million of them die of the disease. Though often a direct cause of infant mortality and an indirect cause of deaths of all ages by lowering the resistance to other infections, the greater impact of malaria on a population lies in its debilitating effects. By limiting the number of conceptions and by causing abortions and stillbirths, malaria affects the birthrate as well as holding down the level of life expectancy. For those patients who survive clinical attacks, it is a continuing drain on physical energy and undoubtedly results in mental retardation. In those countries where malaria is highly endemic, it unquestionably retards the economic development and productivity of the nation. Nearly half the population of the world (well over a billion persons) live in areas where they are exposed to malaria. Under the WHO malaria eradication and control programs, some 466 million people (17 percent of the total population) are, to a greater or lesser extent, protected against the risk, but the remaining 700 million or so (25.7 percent) as yet have no real protection. |