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Isolation and identification of an esterase from a Mexican strain of Boophilus microplus (Acari: Ixodidae).

Pruett JH, Guerrero FD, Hernandez R.

Knipling-Bushland U. S. Livestock Insects Research Laboratory, USDA-ARS-SPA, Kerrville, TX 78028, USA. jhptlab ktc.com

A strain of Mexican Boophilus microplus (Cz) collected near Coatzacoalcos, Veracruz, Mexico, exhibits a moderate, but significant, level of permethrin resistance. Unlike other highly permethrin resistant strains, the Cz strain does not have a mutation within the sodium channel gene that results in target-site insensitivity. However, the Cz strain possesses a substantial increase in general and permethrin esterase activity relative to highly permethrin resistant and control strains suggesting the involvement of a metabolic esterase(s) in the expression of permethrin resistance. We report the isolation of a 62.8 kDa protein from Cz strain larvae that we think is the esterase previously reported as Cz EST9. In addition, internal amino acid sequence data obtained from the 62.8 kDa protein suggest that it is the gene product of a previously reported B. microplus carboxylesterase cDNA. We propose that the 62.8 kDa protein (Cz EST9) has permethrin hydrolytic activity and as a result plays an important role in Cz strain resistance to permethrin.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12403427&dopt=Abstract permethrin Elimite



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Single-dose topical exposure to the pyrethroid insecticide, permethrin in C57BL/6N mice: effects on thymus and spleen.

Prater MR, Gogal RM Jr, Blaylock BL, Longstreth J, Holladay SD.

Department of Biomedical Sciences and Pathobiology, Virginia-Maryland Regional College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg 24061-0442, USA. mrprater vt.edu

Immunomodulatory effects of single topical exposure to permethrin were evaluated in 5-week-old female C57BL/6N mice. Mice exposed to 5-25 microl permethrin (equivalent to 220-1100 mg/kg body weight) on shaved interscapular skin were evaluated for altered body weight; splenic and thymic organ weight and cellularity; thymocyte cell surface expression, cellular apoptosis; splenic macrophage phagocytosis and hydrogen peroxide production; splenic B cell antibody production and T cell cytolytic activity; and mitogen-induced proliferation of splenocytes and thymocytes after in vivo or in vitro permethrin exposure. Topical permethrin application (25 microl) caused 32% inhibition of splenic T cell proliferation; in vitro exposure to permethrin also diminished splenocyte proliferation by 72% at 25 microM and 86% at 100 microM. permethrin did not appear to affect other leukocyte functional assays. Dose-related decreases in thymic cellularity of 52 and 80% were seen in mice exposed to 15 and 25 microl permethrin, respectively. Apoptosis was significantly increased in CD4(-)8(-) and CD4(-)8(+) thymocytes, and the CD4(+)CD8(+) thymocyte subpopulation was most severely diminished, suggesting possible chemical-induced apoptotic mechanism of thymic atrophy. Permethrin also caused splenic hypocellularity by 31% at 15 microl, and by 50% at 25 microl, an effect that may relate to inhibited proliferation or reduced seeding from the hypocellular thymus.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12419701&dopt=Abstract permethrin Elimite



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Indoor pyrethroid exposure in homes with woollen textile floor coverings.

Berger-Preiss E, Levsen K, Leng G, Idel H, Sugiri D, Ranft U.

Fraunhofer Institute of Toxicology and Aerosol Research, Drug Research and Clinical Inhalation, Nikolai-Fuchs-Str. 1, D-30625 Hannover, Germany. berger-preiss ita.fraunhofer.de

In order to investigate human's exposure to permethrin from treated woollen textile floor coverings and possible adverse health effects, a study was carried out in 80 private homes in Hannover (Germany) equipped with woollen textile floor coverings (wool wall-to-wall carpets or woven or knotted rugs). For indoor monitoring, permethrin was determined both in house dust and on suspended particles. While permethrin concentrations in house dust (< 2 mm) were high (arithmetic mean: 53.7 mg/kg, 90th percentile 129.1 mg/kg), the permethrin concentrations in the air (suspended particles) were very low (arithmetic mean 2.8 ng/m3, 90th percentile 5.8 ng/m3, first sampling). Additional experiments demonstrate that permethrin on suspended particles result from carpet fiber abrasion (and not from an evaporation/re-condensation process). The internal exposure of the 145 inhabitants participating in the study was determined by biological monitoring (permethrin metabolites in urine). In a first sampling period almost 14% of the samples showed concentrations of the metabolite DCCA and almost 23% of the metabolite 3-PBA above the limit of detection (0.2 microgram/l). A model was developed which allows the calculation of the metabolite concentration in urine due to inhalative uptake of permethrin. Even for the worst case situation the calculated metabolite concentrations were ca. 30 times lower than the experimental results. The observed concentrations of metabolites are comparable to those of the background concentrations of the general population in Germany, suggesting that they must origin from other sources than woollen textile floor coverings. The indoor and biological monitoring data as well as the evaluation of the reported symptoms give no indication of an adverse health effect due to carpet treatment by permethrin.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12455268&dopt=Abstract permethrin Elimite



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Susceptibility of Haematobia irritans (Diptera: Muscidae) to permethrin in dairies in Aguascalientes, Mexico.

Cruz-Vazquez C, Altamira G, Ramos M, Medina L, Garcia-Vazquez Z, George J.

Instituto Tecnologico Agropecuario de Aguascalientes, AP 74-2, Admon, Postal No. 2, CP 20041, Aguascalientes, Ags, Mexico.

The purpose of this study was to conduct a survey for the susceptibility of the horn fly, Hematobia irritans (L.), populations to permethrin on dairy cattle from Aguascalientes, Mexico. Samples of populations of horn flies at 25 dairies were exposed to two discriminating doses (2.5 and 6.0 microg/cm2) on permethrin-treated filter papers and the percentage of mortality was compared with that of a susceptible strain treated with same doses of permethrin. The results show that there was a difference in the mortality from two discriminating doses and the mortality of the susceptible strain. Therefore, horn fly populations at all dairies tested in Aguascalientes, Mexico, were susceptible to permethrin. This insecticide, as well as other pyrethroids, could continue to be used to provide satisfactory control of horn flies in the study region.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12495197&dopt=Abstract permethrin Elimite



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Pyridostigmine bromide modulates topical irritant-induced cytokine release from human epidermal keratinocytes and isolated perfused porcine skin.

Monteiro-Riviere NA, Baynes RE, Riviere JE.

Center for Chemical Toxicology Research and Pharmacokinetics, North Carolina State University, 4700 Hillsborough Street, Raleigh, NC 27606, USA. nancy_monteiro ncsu.edu

Gulf War personnel were given pyridostigmine bromide (PB) as a prophylactic treatment against organophosphate nerve agent exposure, and were exposed to the insecticide permethrin and the insect repellent N,N-diethyl-m-toluamide (DEET). The purpose of this study was to assess the effects of PB to modulate release of inflammatory biomarkers after topical chemical exposure to chemical mixtures containing permethrin and DEET applied in ethanol or water vehicles. Treatments were topically applied to isolated perfused porcine skin flaps (IPPSFs). Concentrations of interleukin-8 (IL-8), tumor necrosis factor-alpha (TNF-alpha) and prostaglandin E(2) (PGE(2)) were assayed in perfusate to probe for potential inflammatory effects after complex mixture application. IPPSFs (n=4/treatment) were topically dosed with mixtures of permethrin, DEET, and permethrin/DEET, in ethanol. Each treatment was repeated with perfusate spiked with 50 ng/ml of PB. Perfusate was also spiked with 30 ng/ml diisopropylfluorophosphate to simulate low level organophosphate nerve agent exposure. Timed IPPSF venous effluent samples (0.5,1,2,4, and 8 h) were assayed by ELISA for IL-8 and TNF-alpha and by EIA for PGE(2). Overall, PB infusion caused a decrease or IL-8 and PGE(2) release. Effects on TNF-alpha were vehicle dependent. To probe the potential mechanism of this PB effect, human epidermal keratinocyte HEK cell cultures were exposed to permethrin DEET permethrin/DEET, with and without PB in DMSO. IL-8 was assayed at 1, 2, 4, 8, 12 and 24 h. PB suppressed IL-8 in permethrin and ethanol treatment from 4 to 24 h confirming the IPPSF results. In conclusion, these studies suggest that systemic exposure to PB suppressed IL-8 release at multiple time points in two skin model systems. This interaction merits further study.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12504339&dopt=Abstract permethrin Elimite



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Studies on the present status of insecticides resistance on mosquitoes using the diagnostic dosages in El-Fayium Governorate, a spot area of malaria in Egypt.

Mostafa AA, Allam KA.

Research Institute of Medical Entomology, Ministry of Health and Population, Dokki, Giza, Egypt.

Insecticides susceptibility tests were conducted using the World Health Organization diagnostic doses on the adult and larvae of Anopheles pharoensis and Culex pipiens mosquitoes from Fayium Governorate in Egypt. Insecticides used were malathion, fenitrothion, temephos, diazinon, bromophos and fenthion from organophosphorous group and deltamethrin, permethrin and cypermethrin from synthetic pyrethroid group while propoxur was from carbamate group. Larvae of A. pharoensis were resistant to fenitrothion and susceptible to other insecticides used, while the adults were susceptible to malathion, deltamethrin, fenitrothion and premethrin. Larvae of C. pipiens were resistant to temephos, fenitrothion, bromophos and fenthion and susceptible to malathion, permethrin and diazinon, while the adults were resistant to fenitrothion, permethrin and propoxur and susceptible to deltamethrin, cypermethrin and malathion. These results are important for the success of the control programmes and monitoring the susceptibility status of vectors.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=12557941&dopt=Abstract permethrin Elimite