Biomedical subjects
Publications and source records attributed to R Pal.
In Miami, USA, passenger compartments of wide-bodied jet aircraft were disinsected at "blocks away" or while parked. The application of 2% Freon- and water-based formulations of (+)-phenothrin at about 35 g/100 m(3) was highly effective against mosquitos and flies in all instances. More basic research is needed on water-based aerosols.
The recent discovery that Simulium damnosum in Africa is not a single species but a complex of sibling species has important implications for the epidemiology and control of onchocerciasis. This paper sets out the current situation with regard to classification within the S. damnosum complex and the smaller S. neavei group. The nomenclature of the S. damnosum complex and current morphological and enzyme electrophoretic methods of differentiating among sibling species are discussed. Finally, recommendations are made on priorities for future research.
Phytochemical investigation of Tithonia tagitiflora has led to isolation of six new germacranolides, tagitinins A, B, C, D, E, AND F, beta-sitosterol, and its beta-D-glucoside. Among these, tagitinin F possesses antileukemic activity.
A 2% formulation of (+)-phenothrin dispensed from 340-g or break-off tip aerosol cans was highly effective against mosquitos in aircraft disinsection trials. Two minutes after application at "blocks away", the mass median diameter of the dispersed drops was 5.1-6.2 mum. The concentration of the insecticide in the cabin fell to 10% of the original concentration after 9.2 min. No odour or irritation was caused by the use of this insecticide.
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During 1971 worldwide experiments on the disinsection of passenger cabins at "blocks away" (as the aircraft starts taxiing for take-off) were conducted in several types of jet aircraft. A procedure was developed whereby the high capacity Boeing 747 could be disinsected by four stewardesses in less than 1 minute. The favourable results of these and previous trials indicate that this method is suitable as a standard procedure for aircraft disinsection for international quarantine purposes.The biological effectiveness against resistant and non-resistant mosquitos of a 2% concentration of a pyrethroid, resmethrin, in Freon 11+Freon 12 (1:1) (without kerosine) and a favourable passenger response make it suitable as a standard formulation for aircraft disinsection.
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More than 1300 compounds have so far been included in the WHO Programme for Evaluating and Testing New Insecticides, which is designed to disclose compounds that may satisfactorily replace those to which insect vectors of disease have become resistant. The authors describe the successful passage of o-isopropoxyphenyl methylcarbamate (OMS-33) through the first 6 stages of the 7-stage programme that has been established for compounds intended for use against anopheline mosquitos and conclude that this product is suitable for testing in the final stage-large-scale epidemiological evaluation.In operational field trials (at 2 g/m(2)) OMS-33 has been shown capable of controlling Anopheles stephensi (in Iran), An. gambiae and An. funestus (in Nigeria) for 3-4 months, An. albimanus (in El Salvador) for 2-4 months and An. dthali (in Iran) for 2(1/2) months. It has an airborne effect by which anophelines are killed for a considerable time after OMS-33 has been sprayed, even though they do not make contact with a sprayed surface; this quality would appear advantageous in areas where anophelines enter houses and bite man but do not rest long enough on sprayed surfaces to acquire a lethal dose of insecticide or where significant outdoor biting occurs. The observance of simple safety precautions protects occupants of sprayed houses, spraymen and others from danger. Chemical studies have indicated that commercially produced water-dispersible powders of OMS-33 are stable under field conditions of storage and use.
A questionnaire inquiring into the nature of schemes for the insecticidal control of disease vectors, the development of resistance in these vectors, and the effect of any such resistance on their control and on the extent of disease was sent to more than 100 health authorities throughout the world. The replies to the questionnaire are summarized in this paper.Until recently, the use of insecticides in public health has been largely based on three organochlorine compounds-DDT, HCH and dieldrin. However, in some countries resistance to these has now severely affected control both of many insect species and of the diseases they transmit (e.g., malaria, yellow fever, filariasis, typhus, plague). Certain other public health problems (onchocerciasis, Chagas' disease, trypanosomiasis, leishmaniasis) have not so far been greatly affected by resistance, but it is difficult to be sure of the continued reliability of the organochlorines.Research in the past 5 years, much of it sponsored by WHO, has shown the value of various organophosphorus and carbamate insecticides as replacements for the organochlorines, although resistance to them, too, can occur. Attention must therefore be focused on all facets of the use of these newer compounds and particular scrutiny made of possible instances of resistance to them.
During recent years many advances have been made in the development of insect control by genetic manipulation. These methods include the sterile-male technique, now well known, which depends on ionizing radiation or chemosterilization. The recent field experiment carried out by WHO in Rangoon, Burma, on Culex fatigans has demonstrated that naturally occurring cytogenetic mechanisms such as cytoplasmic incompatibility can be used successfully without the use of radiations or chemosterilants. The paper not only describes the experiment on Culex fatigans but also discusses basic concepts and theoretical considerations involved in genetic control of insects of public health importance. The possibility of using genetic mechanisms for the control of other vector species is also discussed. There are a number of problems which require study before genetic control can be used on an operational scale. These problems and suggestions for future research in this field are also outlined.