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Pesticides and the Third World.

Many developing countries are importing industrial processes that make use of toxic chemicals. By the same token, pesticides, which are toxic by design, are also used increasingly in agriculture and in public health programs to control pests and vector-borne diseases. Recent estimates suggest that pesticides account for more than 20,000 fatalities yearly, and that most of these will have occurred in developing countries. This may actually be a gross underreporting. Although organophosphate and carbamate insecticides are still responsible for many of those poisoning cases, herbicides such as paraquat are also increasingly being implicated in fatal poisoning cases. Newer pesticides such as the synthetic derivatives of pyrethrin, which were believed to be relatively safe to humans, now appear to be implicated in some serious cases of intoxication. Community-based pest control using locally available botanical pesticides could have severe consequences unless the toxicity of these compounds is carefully assessed relative to nontarget organisms. A high proportion of pesticide intoxications appear to be due to lack of knowledge, unsafe attitudes, and dangerous practices. The technology available to small farmers for pesticide application is often inappropriate: faulty sprayers, lack of protective equipment adapted to tropical conditions, nonexistent first-aid provisions. Agricultural extension is often not oriented to the transfer of information relative to the dangers inherent in the use of pesticides. The lack of information at all levels may be one of the most important causative factors of chemical intoxication in developing countries. Research should at this time concentrate on behaviors leading to chemical intoxication. This should be done concurrently with proper prospective and retrospective surveys of poisonings in developing country communities. More information should be sought relative to the decision processes of import, legislation, and licensing. Research and development efforts in appropriate technology and safety devices are also critically needed.

Animals↗

Use of household pesticides and the risk of aplastic anaemia in Thailand. The Aplastic Anemia Study Group.

BACKGROUND: Aplastic anaemia is a severe blood dyscrasia that is more common in Thailand than in Western countries. Its a etiology remains poorly understood. METHODS: A case-control study was conducted in Bangkok and two rural regions of Thailand. The effect of household pesticides was evaluated among 253 incident cases of aplastic anaemia and 1174 hospital controls. RESULTS: A total of 54% of the cases and 61% of the controls were exposed 1-6 months previously. For most individual household pesticides and for groups classified according to chemical type (organophosphates, pyrethrins, and organochlorines), the relative risk (RR) estimates approximated 1.0; upper 95% confidence limits were below 2.0 for many comparisons. A significant association was observed for exposure to combination products containing dichlorvos and propoxur, with an overall RR estimate of 1.7 (95% confidence interval [CI]: 1.1-2.6); the estimate for regular use was 1.6 (95% CI: 0.9-2.9). CONCLUSIONS: The absence of a higher risk for the regular use of dichlorvos/propoxur reduces the credibility of the apparent association, which could well have been an artefact of multiple comparisons. We conclude that most household pesticides used in Thailand do not appear to increase the risk of aplastic anaemia.

Adult↗

Susceptibility of house flies (Diptera: Muscidae) and five pupal parasitoids (Hymenoptera: Pteromalidae) to abamectin and seven commercial insecticides.

Assays of five commercial insecticides applied as residual sprays at label rates to plywood indicated the most toxic insecticide overall for pteromalid parasitoids of house flies, Musca domestica L., was Atroban (permethrin), followed by Ciodrin (crotoxyphos), Rabon (tetrachlorvinphos), Ectrin (fenvalerate), and Cygon (dimethoate). Insecticide-susceptible house flies were susceptible to all five insecticides (mortality, 62-100%). Flies that were recently colonized from populations on dairy farms in New York were susceptible only to Rabon. Urolepis rufipes (Ashmead) was the most susceptible parasitoid species overall to these insecticides, followed by Muscidifurax raptor Girault & Sanders, Nasonia vitripennis Walker, Pachycrepoideus vindemmiae (Rondani), and Spalangia cameroni Perkins. Compared with susceptible flies, newly colonized flies showed moderate resistance to avermectin B1a (abamectin). Abamectin was more toxic to all of the parasitoids except N. vitripennis and S. cameroni than to newly colonized house flies when exposed for 90 min to plywood boards treated with 0.001-0.1% abamectin. Space sprays with Vapona (dichlorvos) killed all of the parasitoids and susceptible flies and 64% of the newly colonized flies when insects were placed directly in the path of the spray; mortality was substantially lower among flies and parasitoids protected under 5 cm of wheat straw. Space sprays with Pyrenone (pyrethrins) killed greater than 86% of all insects exposed to the spray path except for the newly colonized flies (1% mortality); mortality of insects protected under straw was low (less than 12%) except for S. cameroni (76%). Because responses of the five parasitoids to the different insecticides varied considerably, general conclusions about parasitoid susceptibility to active ingredients, insecticide class, or method of application were not possible.

Animals↗

Decline of pyrethroid resistance in the absence of selection pressure in a population of German cockroaches (Dictyoptera: Blattellidae).

The level of resistance to seven pyrethroids was followed in a laboratory-selected population of Blattella germanica (L.) for 15 generations, during which time it was not exposed to any insecticide. As estimated by LT50 resistance ratios (RRs), resistance declined in a stepwise manner to preselection levels with all of the pyrethroids except pyrethrins. I also compared the levels of resistance as indicated by RRs and by gene frequency (GF) estimates. Results showed that GF estimates provide a more precise indication of the changes in resistance that occur over time than do RRs alone, especially when combined with RR and end-point mortality data. I discuss my results from the standpoints of the number of genetic mechanisms involved in pyrethroid resistance in this insect, and what the declines in resistance mean for future cockroach control.

Animals↗

Stimulation of vitellogenesis by pyrethroids in mated and virgin female adults, male adults, and fourth instar females of Ornithodoros moubata (Acari: Argasidae).

The effects of several pyrethroids on vitellogenesis, i.e., vitellogenin (Vg) synthesis and ovarian development in unfed mated female adults of Ornithodoros moubata were investigated. Survival of ticks treated with pyrethrin, resmethrin, and etophenprox was very low. Ticks treated with cypermethrin (CyM), fenvalerate (Fev), and flucythrinate (Flu) survived even when high concentrations were used. Vg titer in the hemolymph of unfed mated females was the same level on day 5 and about three times higher on day 10 after treatment with CyM, Fev, and Flu, as that of engorged adult females. CyM was the most effective in inducing vitellogenesis and was further evaluated in unfed virgin females, males, and fourth instars. CyM was shown to stimulate vitellogenesis in unfed virgin females adults. Oviposition did not occur but ovaries were well developed. CyM also was shown to stimulate Vg in the hemolymph of unfed and fed adult males; however, the Vg levels were very low compared to that of engorged adult females. Extremely high concentrations of Vg were observed in the hemolymph of female nymphs (fourth instar), particularly engorged nymphs, treated with CyM (10 micrograms). No ovarian development was observed in these nymphs. Vg stimulated by CyM was shown to be immunologically and electrophoretically the same as that of normal engorged females.

Animals↗

Pediculosis capitis: why prefer a solution to shampoo or spray?

Two hundred and sixty-eight children with pediculosis capitis took part in a comparative study to test the efficacy of five different pediculocides commonly used in Israel. The preparations used were pyrethrin shampoo, pyrethroid spray, malathion solution, carbaryl shampoo and carbaryl lotion. Carbaryl lotion and malathion solution were much more efficient when compared to the shampoo and spray preparations.

Carbaryl↗

Toxins that modulate the sodium channel gating mechanism.

A variety of toxins and chemicals has been shown to modulate the gating kinetics of the sodium channel. Studies of batrachotoxin, grayanotoxins and pyrethroids are summarized here as examples. Batrachotoxin and grayanotoxins eliminate the sodium channel inactivation thereby causing a prolonged, steady-state sodium current to flow during a depolarizing step. The sodium channel activation kinetics are not affected markedly. Batrachotoxin appears to bind to a site in the sodium channel to which the inactivation gate normally binds, thus causing an inhibition of sodium inactivation. Single channel recording experiments have shown that the mean open time of individual sodium channels is greatly prolonged by batrachotoxin. It appears that individual sodium channels are modified by batrachotoxin in an all-or-none manner. Pyrethroids which are synthetic derivatives of pyrethrins also modify the kinetics of sodium channels in a very drastic manner. In the presence of type I pyrethroids which lack a cyano group at the alpha position (e.g., allethrin and tetramethrin), a large steady-state sodium current appears during a step depolarization and a large slowly decaying sodium tail current appears upon repolarization. Thus both the activation and inactivation kinetics are slowed. Type II pyrethroids which contain an alpha-cyano group (e.g., deltamethrin, cyphenothrin, and fenvalerate) exert effects on sodium channels qualitatively similar to those of type I pyrethroids. However, the amplitudes of the steady-state sodium current and sodium tail current are smaller and the time constant of tail current decay is much longer. The mean open time of single sodium channels is greatly prolonged by the pyrethroids, and the effect is much more pronounced in type II than in type I pyrethroids. A high degree of stereospecificity has been found among four isomers of tetramethrin, (+)-trans and (+)-cis isomers being highly active and (-)-trans and (-)-cis isomers almost totally inactive. The inactive isomers bind to the sodium channel sites, thus preventing the action of the active isomers. Because of the unique action of pyrethroids in modulating the sodium channels, they are becoming useful tools for channel physiology and pharmacology.

Action Potentials↗

Systematic review of clinical efficacy of topical treatments for head lice.

OBJECTIVES: To collect and evaluate all trials on clinical efficacy of topical treatments for head lice. DESIGN: Systematic review of randomised trials identified from following data sources: Medline, International Pharmaceutical Abstracts, Science Citation Index, letters to key authors and companies, and hand search of journals. SETTING: Trials in schools or communities. SUBJECTS: Patients infested with lice. MAIN OUTCOME MEASURE: Cure rate (absence of live lice and viable nits) on day 14 after treatment. RESULTS: Total of 28 trials were identified and evaluated according to eight general and 18 lice specific criteria. Of the 14 trials rated as having low to moderate risk of bias, seven were selected as they used the main outcome measure. These seven trials described 21 evaluations of eight different compounds and placebo (all but two evaluations were of single applications). Only permethrin 1% creme rinse showed efficacy in more than two studies with the lower 95% confidence limit of cure rate above 90%. CONCLUSIONS: Only for permethrin has sufficient evidence been published to show efficacy. Less expensive treatments such as malathion and carbaryl need more evidence of efficacy. Lindane and the natural pyrethrines are not sufficiently effective to justify their use.

Administration, Topical↗

Accudosetm aerosol--an effective house fly (Diptera; Muscidae: Musca domestica L.) adulticide control system for cage type poultry houses.

An automatic piped aerosol system (Accudose TM) using 0.7% synergized pyrethrin insecticide, was tested at a typical narrow cage poultry farm for the control of adult house flies, Musca domestica L. A similar narrow cage poultry farm was used as a control with all house fly control measures left up to the cooperating poultryman. AccudoseTM was compared with other house fly control methods at other similar farms which included three types of man-portable ultra volume (ULV) generators and an integrated (biological-chemical) program. Results of the five month test demonstrated that the AccudoseTM system suppressed house fly populations better than other control methods.

Aerosols↗

[Synthetic pyrethroid insecticides and development of resistance to them].

After the structures of pyrethrins, the insecticidal components of pyrethrum flowers, were determined, syntheses of derivatives of them were undertaken, and first generation synthetic pyrethroids, such as allethrin, resmethrin and phenothrin, were produced. Due to lack of photostability in these compounds, their use was limited to the control of sanitary or household pests. The syntheses of second generation synthetic pyrethroids, i.e., permethrin and fenvalerate, overcame a lack of photostability. These are now widely employed in the areas of agriculture and public health. Development of resistance in insect pests is the only difficulty to the future success of ideal insecticides, or synthetic pyrethroides. In this review, information regarding the development of pyrethroid resistance is summerized, and also the importance of nerve insensitivity to the chemicals, as a mechanism of resistance in insects pests, is pointed out.

Animals↗

Urticaria due to airborne permethrin exposure.

Although naturally derived pyrethrins are well recognized sensitizers, there is currently some degree of controversy regarding the sensitizing potential of synthetic pyrethroids. The literature is briefly reviewed, and an outbreak of several cases of urticaria occurring in children from 1 household and associated with airborne exposure to permethrin is reported.

Adult↗

Pediculosis.

Pediculosis can be caused by two distinctly different organisms, the head louse and the pubic louse. Although differing anatomically, they produce equivalent disorders, with itching, bites, and nits on the hairs. The head louse causes disease of the scalp, while the pubic louse lives in short hair in the pubic regions, the body, the axillae, the eyebrows, and the eyelashes. Both can be treated with gamma isomer of hexachlorobenzene, but various mixtures of pyrethrins seem more effective. The body louse, which exactly resembles the head louse, is the only one that can transmit disease. Treatment of body louse infestation is mainly cleanliness: washing the patient and changing his clothing.

Animals↗

Pyrethroid insecticides: stereospecific allosteric interaction with the batrachotoxinin-A benzoate binding site of mammalian voltage-sensitive sodium channels.

Pyrethroid insecticides are synthetic neurotoxins patterned after the naturally occurring pyrethrins. Their mechanism of action is thought to involve effects primarily at the voltage-sensitive sodium channel of both insect and mammalian neurons, although recent studies have raised the possibility that these compounds may also act at the gamma-aminobutyric acid receptor-chloride ionophore complex. Here we show that active pyrethroids of the alpha-cyano-3-phenoxybenzyl class allosterically enhance the binding of [3H]batrachotoxinin-A 20-alpha-benzoate to voltage-sensitive sodium channels of rat brain in a dose-dependent and stereospecific manner. Comparison of the rank order of potency for enhancement of [3H]batrachotoxinin-A 20-alpha-benzoate binding and insecticidal activity in a series of toxic stereoisomers of cypermethrin, representative of the class, reveals a correlation between the two measures. These results support a sodium channel site model for pyrethroid action and suggest a useful and practical method to help evaluate the relationship between effects at the sodium channel and insecticidal potency for members of this class of compounds.

Allosteric Regulation↗

[Methods of reducing the amount of pediculocide residues on bed linens to safe levels].

The means for reducing the residue of organophosphorous and pyrethrin pediculicides on the fabric to safety levels have been developed due to the use of gas and liquid chromatography. The proposed procedures include linen washing after its pediculicidal treatment. Optimal conditions for the removal of the above substances from the fabric have been set forth. Actual quantity of pediculicides on the fabric after its treatment has been identified.

Animals↗

Treatment of public lice infestation: a comparison of two agents.

Bulletins issued by both the United States Public Health Service and the Pan American Health Organization have noted a sharp increase in the incidence of public lice infestation (pediculosis pubis) in this country. At the Haight-Ashbury Free Medical Clinic we conducted a controlled, open study comparing the efficacy and safety of Kwell Shampoo (gamma benzene hexachloride; lindane) with RID, an over-the-counter, pyrethrin-based pediculicide. The results showed the two treatments to be equally effective and safe. All adult lice, nymphs, and nits were eradicated at the one week follow-up in fifteen patients treated with single applications of either product. Two patients in each group experienced very slight and transient erythema.

Administration, Topical↗

Head-lice infestations and their treatment.

Head-lice infestations periodically cause disruption at schools and crèches. The life cycle of the insect and the treatment of infestation are discussed. Treatment is usually relatively simple and effective, relying mainly on the use of insecticides such as gamma benzene hexachloride, malathion and pyrethrins. Appropriate therapy for problem areas, for example the eyebrows, is also described.

Anoplura↗

Species and structural variations affecting pyrethroid neurotoxicity.

Pyrethroids provide fascinating patterns and examples of species selectivity resulting from variations in nerve sensitivity and detoxification rates. Three classification systems are useful in considering pyrethroids: origin, structure, stability and use relative to the natural pyrethrin I; lethal and sublethal or knockdown agents; Types I and II symptoms and nerve action. Pyrethroid-detoxifying esterases and oxidases contribute importantly to the species and strain specificity and provide an opportunity to use inhibitors as synergists for improved effectiveness. Pyrethroids are potent and selective neuropharmacological agents inducing repetitive discharges or conduction block in a variety of sensory and motor nerves and in the CNS. Small structural modifications in the pyrethroid often change the type of action as well as the potency and species specificity. Pyrethroid resistance in selected strains of insect pests may involve a modified and pyrethroid-insensitive target site.

Animals↗

[Pediculosis capitis: a questionnaire survey in 4 schools of the Bordeaux Academy 1990-1991].

A questionnaire survey of head lice treatment was conducted in four schools--each including a nursery and an elementary school--in the Bordeaux area. Two schools were situated in the centre of the city, one in a suburban area and one in a rural area (50 km from the city). Four-page questionnaires were filled in anonymously by the parents in April 1991; 840 answers were obtained (80 p. 100 response rate). Between January 1990 and March 1991, 48.7 p. 100 of children had at least one episode of head lice infestation (infestation rates varied from 38.8 to 62.6 p. 100 depending on the schools); 30.5 p. 100 of children were contaminated for the first time during that period. Lice were detected by the parents in 95 p. 100 of the cases. The prevalence of lice was higher in females (60 p. 100) than in males (40 p. 100). The highest prevalence was noted in the suburban school where 17 p. 100 of the parents were unemployed at the time of the survey. The peak age for head lice was 7, but 19.4 p. 100 of nursery school children aged 2-4 years had been contaminated at least once. Impetigo was rare (1.2 p. 100), and pruritus was noted in only 14.2 p. 100 of the cases. Most children had been contaminated at school. Curative treatment was counselled by a chemist in 87 p. 100 of the cases. Pyrethrins were used in 81 p. 100, and the shampoo (Hegor) plus spray (Paraspecial Poux) association was the most frequent, totalling two-thirds of prescriptions.(ABSTRACT TRUNCATED AT 250 WORDS)

Child↗