cyhalothrin and Chagas-Disease

The use of insecticide treated materials for the control of Chagas' disease transmission is potentially a cost-effective and sustainable option where vectors are sylvatic. A study was undertaken in two rural Chagas' disease endemic communities (96 households) of Trujillo State, Venezuela. After a baseline study (including a short questionnaire survey, assessment of housing conditions, vector behaviour and preferences in vector protection), 37 households were chosen at random for protection by impregnated or non-impregnated curtains. During the 30-day entomological study vector collection of triatomine bugs were conducted in the early morning. The protective efficacy of curtains was determined by the number of vectors found dead or alive in control and experimental houses. It was found that house infestation of Chagas' disease vectors was high (60% of houses) in spite of good-quality houses due to a re-housing programme. The vectors were sylvatic (mainly Rhodnius robustus) and entered the houses at night. More than half the population (52%) preferred curtains to bednets for Chagas' disease protection. Users of pyrethroid-impregnated curtains were well protected as no living triatomines were found in bedrooms of houses with impregnated curtains compared to houses with non-impregnated curtains where an average of 4/7 vectors were found alive in bedrooms. In houses with impregnated curtains 21/30 triatomines died within 72 h; the triatomines which survived were found exclusively in rooms where no impregnated curtains had been placed. In houses with non-impregnated curtains 20% (6/30) of vectors died, probably due to rough handling. It is concluded that pyrethroid-impregnated curtains represent an important option for the reduction or even elimination of man-vector contact and thus of Chagas' disease transmission in areas where species of small triatomine bugs such as Rhodnius prolixus and R. robustus are the main vectors.

Topics: Adult; Animals; Chagas Disease; Disease Vectors; Housing; Humans; Insecticides; Mosquito Control; Nitriles; Poverty; Pyrethrins; Rhodnius; Rural Population; Venezuela

Systematic evaluation of the susceptibility of disease vectors to insecticides permits the detection of the development of insecticide resistance over time. This is necessary to evaluate the effectiveness of control methods and to plan management strategies of the resistance.. The baseline susceptibility was determined for I and V instar nymphs of Rhodnius pallescens to the active ingredients of the insecticides deltamethrin and lambdacyhalothrin.. The bioassays were applied to two field populations of R. pallescens collected in Chilibre and Cerro Cama, Panamá. A standard protocol for topical application was adapted from that developed for Rhodnius prolixus. Bioassays were performed using topical applications on the dorsal abdominal surface, with volumes of 0.1µl and 0.5µl acetone solution of insecticide for nymphs of stage I and V respectively, using 5µl and 25µl Hamilton microsyringes with a repeating dispenser. Ten nymphs were used for each insecticide concentration. Results. With the topical application of lambdacyhalothrin on first-instar nymphs from Chilibre and Cerro Cama, the LD50 values expressed in ng/insect were 0.13 and 0.11 respectively. In fifth-instar nymphs the LD50 values were 1.71 and 3.48, respectively. For deltamethrin, the topical application on first-instar nymphs resulted in LD50 values of 0.02 and 0.02, and in fifth-instar nymphs the LD50 values were 2.11 and 1.55, respectively.. In I and V instar nymphs from the two R. pallescens populations, resistance factor values demonstrated no significant difference in the toxic effects of the two insecticides and indicated that the R. pallescens populations were susceptible them.

Topics: Administration, Topical; Animals; Biological Assay; Chagas Disease; Humans; Insect Vectors; Insecticide Resistance; Insecticides; Lethal Dose 50; Nitriles; Panama; Pyrethrins; Rhodnius

The insecticidal activity and residual effect of two formulations of lambdacyhalothrin were evaluated with Rhodnius prolixus; laboratory and field tests were conducted in the State of Chiapas, Mexico. The results indicate that the lethal concentrations of the active ingredient of SC (LC50 = 2.37 and LC90 = 8.5 mg, a.i./m2) were 4-8 times than those with the insecticide WP applied on R. prolixus bugs in palm leaves, a common building material for thatched roofs. Other investigators in South America recommended applying 30 mg a.i./m2 in porous materials; we obtained that the products WP and SC were 3.5 and 16 times more effective on palm leaves. Regarding the evaluation of the residual effects in field spraying, there was up to 15 months persistence after the application of WP in two doses (8.6 mg a.i./m2 and 3.752 mg a.i./m2) with SC. We consider R. prolixus highly susceptible to the employed pyrethroids; they could be used to control this vector in the state of Chiapas, Mexico.

Topics: Animals; Biological Assay; Chagas Disease; Insect Vectors; Insecticide Resistance; Insecticides; Mexico; Mosquito Control; Nitriles; Pyrethrins; Rabbits; Rhodnius