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Biomedical subjects

G MACDONALD

Publications and source records attributed to G MACDONALD.

At least 19 recordsLinked to original sources
PubMed1964

THE MALARIA PARASITE RATE AND INTERRUPTION OF TRANSMISSION.

Present methods for assessment of the attack phase of malaria eradication are inadequate, particularly lacking any objective parasitological criteria of success. On the basis of previous observations and development of theory, the authors first postulate that the effects of complete interruption of transmission should, ideally, include a regular progressive decrease of falciparum parasite rates in the ratios of 1: 0.4 in 6 months, 1: 0.16 in 12 months and 1: 0.026 in 24 months. Analysis of a series of programmes in which complete interruption of transmission is known to have been achieved shows that this postulate is valid, and that it is not materially upset by strain differences of parasites or by differences in the ages of the subjects examined. Vivax rates appear to fall at approximately the same rate; the rarity of data for vivax malaria makes firm conclusions unsure, but the postulate can be extended to rates which are predominantly due to falciparum infection but include some admixture of other species. A second, arbitrary, postulate is made that the slowest acceptable rate of fall in 12 months should be in a ratio not less than 1: 0.22, which would secure ultimate eradication in about one-third more time than the ideal fall; on this basis statistical standards are set up for assurance of confidence that the minimum rate is exceeded. Slower rates of fall are then related to reproduction rates causing them, the findings being illustrated graphically and by mathematical theory.

Animals↗
PubMed1956

Theory of the eradication of malaria.

The natural disappearance of malaria from certain areas-a phenomenon which has for many years been observed in various parts of the world-is discussed in relation to the recent deliberate elimination of the disease from large tracts of land. The process of elimination, the detection of residual foci, and the ways in which the disease may be reintroduced into a country are outlined briefly, and the course of events in epidemics which arise from small origins is described in detail. The factors affecting the basic reproduction rate in such epidemics-mean duration of infectivity of a primary malaria case, density of mosquitos in relation to man, and longevity and degree of anthropophilism of the vector concerned-are analysed, and a simplified method of expressing this rate mathematically is given in an annex.

Humans↗
PubMed1956

Epidemiological basis of malaria control.

The epidemiology of malaria is discussed with special reference to the pattern observed in equatorial Africa, where the disease is very stable and where certain features, such as severe epidemic tendencies and ready amenability to control, commonly found in other malarious regions, are lacking. The particular conditions giving rise to stability are described in detail, and the ways in which they can be modified to bring about control of the disease in its stable form are outlined. The importance of measuring certain rates-for example, the basic reproduction rate, the index of stability, and the actual reproduction rate-when making any major malaria survey is emphasized, and formulae by means of which such rates can be readily calculated are included in an annex.

Africa↗
PubMed1953

Dose and cycle of insecticide applications in the control of malaria.

The authors first review the doses and cycles of application normally recommended in different parts of the world for DDT, BHC, and dieldrin in controlling malaria, and then discuss the experimental evidence concerning their actual efficacy in the field. The irritant effect of the various insecticides is compared, DDT being found the most irritant and dieldrin the least. BHC appears to be highly irritant when solid, but not when vaporized. The problem of the application of residual insecticides to absorbent surfaces, such as mud, is considered; the wettable powders are generally accepted as the most efficient formulation for such surfaces, but even with these a marked loss in toxicity may occur, requiring higher initial doses and more frequent application than on non-absorbent surfaces. With volatile insecticides, such as BHC, some degree of absorption slows down the loss by volatilization, but at the usual field dosages of 0.1 g and 0.2 g of gamma-BHC per m(2) the decline in toxicity is still rapid. Experiments have also shown that mixtures of DDT and BHC may, in some circumstances, combine the initial high kill of the latter with the persistent moderate kill of the former.Considering the insecticidal efficiency needed for the control of malaria, the authors find that most natural circumstances would be met by attaining a mortality-rate of about 65% of mosquitos entering treated shelters; 85% mortality would be suitable for the most severe conditions and 65% mortality for controlling moderate transmission by endophilic mosquitos.

Animals↗