Mosquito carrier

The name of this insecticide is to many people synonymous with environmental pollution, and it is therefore an important example in this chapter but the story is not simple. DDT is an abbreviation for the chemical name of the insecticide dichloro-diphenyl-trichloroethane. It contains five chlorine atoms and is hence called an organochlorine compound. It was first made in 1874 but not found to be an insecticide until 1939 by Paul Muller. It was used extensively in the Second World War for the control of insects such as lice and mosquitoes, carriers of the diseases typhus and malaria. It was very effective in controlling these pests, and the diseases they carried, and undoubtedly thousands of soldiers lives were saved. Since then, the lives of millions of people throughout the world have also been saved by this insecticide both as a result of the reduction of these and other diseases and as a result of the improvement in crop yields which has reduced starvation. Indeed, in 1953 it was estimated that the use of DDT for malaria eradication had saved 50 million lives and averted more... 

In 1978, WHO announced that it was extensively using chlorpyriphos and fenthion to control the Culex mosquito vector of filariasis these are respectively 0,0 -diethyl O" -(3,5,6-trichloropyrid-2-yl) phosphorothioate and 0,0 -dimethyl 0"-(3-methyl-4-methylthiophenyl) phosphorothioate. Against Aedes mosquitoes, carriers of dengue and yellow fever viruses, they were using temephos 0,0 -(thiodi-4,i-phenylene) 0,0,0, 0 -tetramethyl phosphorothioate. To supplement their control of anopheline mosquitoes (vectors of the malarial parasites) they had introduced brom-ophos, iodfenphos, and pirimiphos-methyl, which are respectively 0-(4-bromo-2,5-dichlorophenyl) 0, 0"-dimethyl phosphorothioate ... 

Granulars are pelleted mixtures of toxicant, usually at 2.5 ndash 10%, and a dust carrier, eg, absorptive clay, bentonite, or diatomaceous earth, and commonly are 250 ndash 590 ]lni in particle size. They are prepared by impregnation of the carrier with a solution or slurry of the toxicant and are used principally for mosquito larviciding and soil appHcations. 

Rates of malaria continue to increase over the years between 1970 and 1997 there was a 40% increase in malaria rates in sub-Saharan Africa alone. In the mid-f 950s, the World Health Organization launched a massive campaign to eliminate malaria from the globe. The initiative was initially successful and combined insecticide use and drug treatment malaria was conquered completely in some areas and sharply curbed in others. However, nature eventually intervened. Anopheles mosquitoes, the carriers of malaria, became resistant to DDT and other insecticides used in their elimination. 

Mosquitoes, are the most notorious carriers, or vectors, of disease and parasites. Female mosquitoes rely on warm-blooded hosts to serve as a blood meal to nourish their eggs. During the process of penetrating a host s skin with their long, sucking mouth parts, saliva from the mosquito is transferred into the bite area. Any viral, protozoan, or helminth infections carried in the biting mosquito can be transferred directly into the blood stream of its host. Among these are malaria, yellow fever, W. bancrofti (filariasis and elephantiasis), and D. immitis (heartworm). 

Once again, there are striking parallels in human epidemics with the development of resistant strains of viral and bacterial diseases and resistant vectors of disease. See John Wargo s discussion of malaria and its carrier, the Anopheles mosquito, in Our Children s Toxic Legacy How Science and Law Fail to Protect Us from Pesticides (New Haven Yale University Press, 1996), pp. 15-42. 

An alternative, more specialized procedure for small-scale use involves the use of vaporizing devices in which a high concentration of an insecticide is dispersed on a solid carrier from which during heating (mosquito mats) or burning (smokes or mosquito coils), or sometimes at mom temperature (impregnated plastic strips), an insecticidal vapour is produced. When used in such products PBO acts more as a solvent or evaporation retardant which evens out the rate of volatilization than as a synergist. 

The importance of insect-home diseases fully recognized in Africa and India has often been underestimated in developed countries, and mosquitoes, (lies and cockroaches may be regarded more as nuisance pests rather than carriers of discascs. 

Vector a carrier especially the animal or intermediate host that carries a pathogen from one host to another. Examples of vectors include mosquitoes, fleas, ticks, and lice. 

FIGURE 13.16 Two adult female, 4no/ Ae/es gambiae mosquitoes (ventral view). The one on the left is a mutant. Scientists are attempting to produce strains of these mutant mosquitoes, which are unahle to transmit malaria to humans, in hopes that they will replace the malaria carriers. 

Researchers beheve that carriers of a G6PD mutation may be partially protected against malaria, an infectious disease carried by a certain type of mosquito. A reduction in the amount of functional glucose-6-dehydrogenase appears to make it more difficult for this parasite to invade red blood cells. Glucose-6-phosphate dehydrogenase deficiency occurs most frequently in areas of the world where malaria is common. 

Q Nevertheless, Giovanni Maria Lands (1654-1720) an Italian physician and epidemiologist, had already postulated in 1717 in his monograph, titled "Noxious Emanations of Swamps and Their Cure" mosquitoes as potential carriers of the disease. 

Mike Fink, an epidemiology specialist for the Arizona Department of Health Services, separates the Culex genus mosquito, the carrier of the West Nile virus, from other mosquitos caught in a traps placed in suspected areas throughout the state at the department s lab August 5, 2004 in Phoenix, Arizona. (Getty Images)... 

Oddly, the first use of Redux was not in a metal aircraft or to bond Gordon Aerolite components but in the essentially all-wood, long-range versions of the Mosquito the de Havilland DH103 Hornet and Sea Hornet the latter was the version intended for naval carrier use [11,18,19]. 

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